New articles on astro-ph


[1] 2007.01856

$^{26}$Al-$^{26}$Mg isotopic, mineralogy, petrography of a Hibonite-Pyroxene Spherule in Allan Hills 77307 (CO3.03): Implications for the origin and evolution of these objects

10 Hibonite-pyroxene/glass spherules discovered hitherto are a rare suite of refractory inclusions that show the largest range of exotic isotopic properties (anomalies in neutron rich isotopes (e.g., $^{48}$Ca, $^{50}$Ti), abundance of $^{26}$Al) despite their defining simple spherical morphology and mineralogy consisting predominantly of few hibonites nestled within/with glassy or crystallised calcium, aluminium-rich pyroxene. $^{26}$Al-$^{26}$Mg chronological studies along with petrography and mineralogy of a relatively large (~120 micron diameter), found in Allan Hills 77307 (CO3.03) has been performed. Uniquely, both hibonite and pyroxene show discordant abundance of short-lived now-extinct radionuclide $^{26}$Al that suggest disparate and distinct regions of origin of hibonite and pyroxene. The pristine petrography and mineralogy of this inclusion allow discernment of their genesis and trend of alteration in hibonite-pyroxene/glass spherules.


[2] 2007.01868

Dalek -- a deep-learning emulator for TARDIS

Supernova spectral time series contain a wealth of information about the progenitor and explosion process of these energetic events. The modeling of these data requires the exploration of very high dimensional posterior probabilities with expensive radiative transfer codes. Even modest parametrizations of supernovae contain more than ten parameters and a detailed exploration demands at least several million function evaluations. Physically realistic models require at least tens of CPU minutes per evaluation putting a detailed reconstruction of the explosion out of reach of traditional methodology. The advent of widely available libraries for the training of neural networks combined with their ability to approximate almost arbitrary functions with high precision allows for a new approach to this problem. Instead of evaluating the radiative transfer model itself, one can build a neural network proxy trained on the simulations but evaluating orders of magnitude faster. Such a framework is called an emulator or surrogate model. In this work, we present an emulator for the TARDIS supernova radiative transfer code applied to Type Ia supernova spectra. We show that we can train an emulator for this problem given a modest training set of a hundred thousand spectra (easily calculable on modern supercomputers). The results show an accuracy on the percent level (that are dominated by the Monte Carlo nature of TARDIS and not the emulator) with a speedup of several orders of magnitude. This method has a much broader set of applications and is not limited to the presented problem.


[3] 2007.01870

NGC 474 as viewed with KCWI: diagnosing a shell galaxy

We present new spectra obtained using Keck/KCWI and perform kinematics and stellar population analyses of the shell galaxy NGC 474, from both the galaxy centre and a region from the outer shell. We show that both regions have similarly extended star formation histories although with different stellar population properties. The central region of NGC 474 is dominated by intermediate-aged stars (8.3 \pm 0.3 Gyr) with subsolar metallicity ([Z/H]= -0.24 \pm 0.07 dex) while the observed shell region, which hosts a substantial population of younger stars, has a mean luminosity-weighted age of 4.0 \pm 0.5 Gyr with solar metallicities ([Z/H]=-0.03 \pm 0.09 dex). Our results are consistent with a scenario in which NGC 474 experienced a major to intermediate merger with a log\((M_*/M_\odot)\sim10 \) mass satellite galaxy at least \sim 2 Gyr ago which produced its shell system. This work shows that the direct spectroscopic study of low-surface brightness stellar features, such as shells, is now feasible and opens up a new window to understanding galaxy formation and evolution.


[4] 2007.01871

Evidence for a high mutual inclination between the cold Jupiter and transiting super Earth orbiting $π$ Men

$\pi$ Men hosts a transiting super Earth ($P\approx6.27$ d, $m\approx4.82$ $M_{\oplus}$, $R\approx2.04$ $R_{\oplus}$) discovered by TESS and a cold Jupiter ($P\approx2093$ d, $m \sin I\approx10.02$ $M_{\rm{Jup}}$, $e\approx0.64$) discovered from radial velocity. We use Gaia DR2 and Hipparcos astrometry to derive the star's velocity caused by the orbiting planets and constrain the cold Jupiter's sky-projected inclination ($I_b=41-65^{\circ}$). From this we derive the mutual inclination ($\Delta I$) between the two planets, and find that $49^{\circ}< \Delta I < 131^{\circ}$ (1$\sigma$), and $28^{\circ} < \Delta I < 152^{\circ}$ (2$\sigma$). We examine the dynamics of the system using $N$-body simulations, and find that potentially large oscillations in the super Earth's eccentricity and inclination are suppressed by General Relativistic precession. However, nodal precession of the inner orbit around the invariable plane causes the super Earth to only transit between 7-22 per cent of the time, and to usually be observed as misaligned with the stellar spin axis. We repeat our analysis for HAT-P-11, finding a large $\Delta I$ between its close-in Neptune and cold Jupiter and similar dynamics. $\pi$ Men and HAT-P-11 are prime examples of systems where dynamically hot outer planets excite their inner planets, with the effects of increasing planet eccentricities, planet-star misalignments, and potentially reducing the transit multiplicity. Formation of such systems likely involves scattering between multiple giant planets or misaligned protoplanetary discs. Future imaging of the faint debris disc in $\pi$ Men and precise constraints on the stellar spin orientation would provide strong tests for these formation scenarios.


[5] 2007.01872

Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius "Tilted Disk" of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least $48\%$ ionized. The ratio [NII] $\lambda$6584 $\overset{\lower.5em\circ}{\mathrm{A}}$/H$\alpha$ $\lambda$6563 $\overset{\lower.5em\circ}{\mathrm{A}}$ increases from 0.3 to 2.5 with Galactocentric radius; [OIII] $\lambda$5007 $\overset{\lower.5em\circ}{\mathrm{A}}$ and H$\beta$ $\lambda$4861 $\overset{\lower.5em\circ}{\mathrm{A}}$ are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.


[6] 2007.01874

The Effect of Bars on the Ionized ISM: Optical Emission Lines from Milky Way Analogs

Gas interior to the bar of the Milky Way has recently been shown as the closest example of a Low Ionization (Nuclear) Emission Region--LI(N)ER--in the universe. To better understand the nature of this gas, a sample of face-on galaxies with integral field spectroscopy are used to study the ionized gas conditions of 240 barred and 250 nonbarred galaxies, focusing on those that are most similar to the Milky Way. Strong optical line emission of $[NII]$ $\lambda 6584$, H$\alpha$, $[OIII]$ $\lambda 5007$, and H$\beta$ are used to diagnose the dominant ionization mechanisms of gas across galaxies and the Galaxy via Baldwin-Phillips-Terlevich (BPT) Diagrams. Barred galaxies show a strong suppression of star formation and an increase in composite and LI(N)ER like spectra in their inner regions when compared with similar nonbarred counterparts. This effect is lessened in galaxies of very low ($\log_{10}(M_\star/M_\odot) \lesssim 10.4$) or very high ($\log_{10}(M_\star/M_\odot) \gtrsim 11.1$) total stellar mass. Bar masks from Galaxy Zoo:3D show the bar's non-axisymmetric effect on the ionized gas and help predict the face-on distribution of ionized gas conditions near the bar of the Milky Way.


[7] 2007.01875

Implementation of stellar heating feedback in simulations of star cluster formation: effects on the initial mass function

Explaining the initial mass function (IMF) of stars is a long-standing problem in astrophysics. The number of complex mechanisms involved in the process of star cluster formation, such as turbulence, magnetic fields and stellar feedback, make understanding and modeling the IMF a challenging task. In this paper, we aim to assert the importance of stellar heating feedback in the star cluster formation process and its effect on the shape of the IMF. We use an analytical sub-grid model to implement the radiative feedback in fully three-dimensional magnetohydrodynamical (MHD) simulations of star cluster formation, with the ultimate objective of obtaining numerical convergence on the IMF. We compare a set of MHD adaptive-mesh-refinement (AMR) simulations with three different implementations of the heating of the gas: 1) a polytropic equation of state (EOS), 2) a spherically symmetric stellar heating feedback, and 3) our newly developed polar heating model that takes into account the geometry of the accretion disc and the resulting shielding of stellar radiation by dust. For each of the three heating models, we analyse the distribution of stellar masses formed in ten molecular cloud simulations with different realizations of the turbulence to obtain a statistically representative IMF. We conclude that stellar heating feedback has a profound influence on the number of stars formed and plays a crucial role in controlling the IMF. We find that the simulations with the polar heating model achieve the best convergence on the observed IMF.


[8] 2007.01877

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

The density structure of the interstellar medium (ISM) determines where stars form and release energy, momentum, and heavy elements, driving galaxy evolution. Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scale and galactic environment. Although dense star-forming gas likely emerges from a combination of instabilities, convergent flows, and turbulence, establishing the precise origin is challenging because it requires quantifying gas motion over many orders of magnitude in spatial scale. Here we measure the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span an unprecedented spatial dynamic range ($10^{-1}{-}10^3$ pc). We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from $0.3{-}400$ pc. These flows are coupled to regularly-spaced density enhancements that likely form via gravitational instabilities. We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows. Our results demonstrate that ISM structure cannot be considered in isolation. Instead, its formation and evolution is controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.


[9] 2007.01878

XV. The mean rest-UV spectra of Ly-alpha emitters at z>3

We investigate the ultraviolet (UV) spectral properties of faint Lyman-$\alpha$ emitters (LAEs) in the redshift range 2.9<z<4.6 and provide material to prepare future observations of the faint Universe. We use data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median M$_{UV}$ of -18 and down to M$_{UV}$ of -16), low stellar mass (median value of $10^{8.4}$ and down to $10^{7}M_{\odot}$) LAEs at redshift z>3. We compute various averaged spectra of LAEs sub-sampled on the basis of their observational (e.g., Ly$\alpha$ strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We search for UV spectral features other than Ly$\alpha$, such as higher-ionization nebular emission lines and absorption features. We successfully observe the OIII]1666 and CIII]909 collisionally excited emission lines and the HeII1640 recombination feature, as well as the resonant CIV1550 doublet either in emission or P-Cygni. We compare the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly$\alpha$ equivalent widths, fainter UV magnitudes, bluer UV spectral slopes and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z>2 galaxies. This suggests that weak UV features are likely ubiquitous in high z, low-mass and faint LAEs. We publicly release the stacked spectra as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.


[10] 2007.01880

Measuring the total infrared light from galaxy clusters at z=0.5-1.6: connecting stellar populations to dusty star formation

Massive galaxy clusters undergo strong evolution from z~1.6 to z~0.5, with overdense environments at high-z characterized by abundant dust-obscured star formation and stellar mass growth which rapidly give way to widespread quenching. Data spanning the near- to far-infrared (IR) spectrum can directly trace this transformation; however, such studies have largely been limited to the massive galaxy end of cluster populations. In this work, we present ``total light" stacking techniques spanning 3.4-500{\mu}m aimed at revealing the total cluster IR emission, including low mass members and potential intracluster dust. We detail our procedures for WISE, Spitzer, and Herschel imaging, including corrections to recover the total stacked emission in the case of high fractions of detected galaxies. We apply our stacking techniques to 232 well-studied massive (log M200/Msun~13.8) clusters across multiple z bins, recovering extended cluster emission at all wavelengths, typically at >5sigma. We measure the averaged near- to far-IR radial profiles and SEDs, quantifying the total stellar and dust content. The near-IR radial profiles are well described by an NFW model with a high (c~7) concentration parameter. Dust emission is similarly concentrated, albeit suppressed at small radii (r<0.2Mpc). The measured SEDs lack warm dust, consistent with the colder SEDs expected for low mass galaxies. We derive total stellar masses consistent with the theoretical Mhalo-M_star relation and specific-star formation rates that evolve strongly with redshift, echoing that of massive (log Mstar/Msun>10) cluster galaxies. Separating out the massive galaxy population reveals that the majority of cluster far-IR emission (~70-80%) is provided by the low mass constituents, which differs from field galaxies. This effect may be a combination of mass-dependent quenching and excess dust in low mass cluster galaxies.


[11] 2007.01885

Submillimetre galaxies in cosmological hydrodynamical simulations -- an opportunity for constraining feedback models

Submillimetre galaxies (SMGs) have long posed a challenge for theorists, and self-consistently reproducing the properties of the SMG population in a large-volume cosmological hydrodynamical simulation has not yet been achieved. In this work, we employ a relatively simple method based on previous work to predict the submm flux densities of simulated SMGs drawn from cosmological simulations from the Illustris and IllustrisTNG projects and compare the predicted number counts with observations. We find that the predicted SMG number counts based on IllustrisTNG are significantly less than observed (more than 1 dex at $S_{850} \gtrsim 4$ mJy). The simulation from the original Illustris project yields more SMGs than IllustrisTNG: the predicted counts are consistent with those observed at both $S_{850} \lesssim 5$ mJy and $S_{850} \gtrsim 9$ mJy and only a factor of $\sim 2$ lower than observed at intermediate flux densities. We demonstrate that IllustrisTNG hosts fewer SMGs than Illustris because in the former, high-mass ($M_{\star} \sim 10^{11} \, {\rm M}_{\odot}$) $z \sim 2-3$ galaxies have lower dust masses and star formation rates (SFRs) than in Illustris owing to differences in the sub-grid models for stellar or/and active galactic nucleus (AGN) feedback between the two simulations (we unfortunately cannot isolate the specific cause(s) post hoc). Our results demonstrate that because our method enables predicting SMG number counts in post-processing with a negligible computational expense, SMGs can provide useful constraints for tuning sub-grid models in future large-volume cosmological simulations. Higher resolution, which would lead to stronger SFR enhancements in starbursts, could at least partially reconcile the discrepancy between the IllustrisTNG SMG number counts and those observed.


[12] 2007.01887

Supernova Triggers for End-Devonian Extinctions?

The Late Devonian was a protracted period of low speciation resulting in biodiversity decline, culminating in extinction events near the Devonian-Carboniferous boundary. Recent evidence indicates that the final extinction event may have coincided with a dramatic drop in stratospheric ozone, possibly due to a global temperature rise. Here we study an alternative possible cause for the postulated ozone drop: a nearby supernova explosion that could inflict damage by accelerating cosmic rays that can deliver ionizing radiation for up to $\sim 100$ kyr. We therefore propose that end-Devonian extinction was triggered by one or more supernova explosions at $\sim 20 \ \rm pc$, somewhat beyond the ``kill distance'' that would have precipitated a full mass extinction. Nearby supernovae are likely due to core-collapses of massive stars in clusters in the thin Galactic disk in which the Sun resides. Detecting any of the long-lived radioisotopes \sm146, \u235 or \pu244 in one or more end-Devonian extinction strata would confirm a supernova origin, point to the core-collapse explosion of a massive star, and probe supernova nucleosythesis. Other possible tests of the supernova hypothesis are discussed.


[13] 2007.01889

Joint galaxy-galaxy lensing and clustering constraints on galaxy formation

We compare predictions for galaxy-galaxy lensing profiles and clustering from the Henriques et al. (2015) public version of the Munich semi-analytical model of galaxy formation (SAM) and the IllustrisTNG suite, primarily TNG300, with observations from KiDS+GAMA and SDSS-DR7 using four different selection functions for the lenses (stellar mass, stellar mass and group membership, stellar mass and isolation criteria, stellar mass and colour). We find that this version of the SAM does not agree well with the current data for stellar mass-only lenses with $M_\ast > 10^{11}\,M_\odot$. By decreasing the merger time for satellite galaxies as well as reducing the radio-mode AGN accretion efficiency in the SAM, we obtain better agreement, both for the lensing and the clustering, at the high mass end. We show that the new model is consistent with the signals for central galaxies presented in Velliscig et al. (2017). Turning to the hydrodynamical simulation, TNG300 produces good lensing predictions, both for stellar mass-only ($\chi^2 = 1.81$ compared to $\chi^2 = 7.79$ for the SAM), and locally brightest galaxies samples ($\chi^2 = 3.80$ compared to $\chi^2 = 5.01$). With added dust corrections to the colours it matches the SDSS clustering signal well for red low mass galaxies. We find that both the SAMs and TNG300 predict $\sim 50\,\%$ excessive lensing signals for intermediate mass red galaxies with $10.2 < \log_{10} M_\ast [ M_\odot ] < 11.2$ at $r \approx 0.6\,h^{-1}\,\mathrm{Mpc}$, which require further theoretical development.


[14] 2007.01906

Precise calibration of the dependence of surface brightness-colour relations on colour and class for late-type stars

Surface brightness-colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars. We aim to calibrate new SBCRs as a function of the spectral type and the luminosity class of the stars. Our goal is also to apply homogeneous criteria to the selection of the reference stars and in view of compiling an exhaustive and up-to-date list of interferometric late-type targets. We implemented criteria to select measurements in the JMMC Measured Diameters Catalog (JMDC). We then applied additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics. We built SBCRs for F5/K7-II/III, F5/K7-IV/V, M-II/III and M-V stars, with respective RMS of $\sigma_{F_{V}} = 0.0022$ mag, $\sigma_{F_{V}} = 0.0044$ mag, $\sigma_{F_{V}} = 0.0046$ mag, and $\sigma_{F_{V}} = 0.0038$ mag. This results in a precision on the angular diameter of 1.0\%, 2.0\%, 2.1\%, and 1.7\%, respectively. These relations cover a large $V-K$ colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the Gaia photometry for our samples, we obtained (G-K) SBCRs with a precision on the angular diameter between 1.1\% and 2.4\%.


[15] 2007.01910

The miniJPAS survey: a preview of the Universe in 56 colours

The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) will soon start to scan thousands of square degrees of the northern extragalactic sky with a unique set of $56$ optical filters from a dedicated $2.55$m telescope, JST, at the Javalambre Astrophysical Observatory. Before the arrival of the final instrument (a 1.2 Gpixels, 4.2deg$^2$ field-of-view camera), the JST was equipped with an interim camera (JPAS-Pathfinder), composed of one CCD with a 0.3deg$^2$ field-of-view and resolution of 0.23 arcsec pixel$^{-1}$. To demonstrate the scientific potential of J-PAS, with the JPAS-Pathfinder camera we carried out a survey on the AEGIS field (along the Extended Groth Strip), dubbed miniJPAS. We observed a total of $\sim 1$ deg$^2$, with the $56$ J-PAS filters, which include $54$ narrow band (NB, $\rm{FWHM} \sim 145$Angstrom) and two broader filters extending to the UV and the near-infrared, complemented by the $u,g,r,i$ SDSS broad band (BB) filters. In this paper we present the miniJPAS data set, the details of the catalogues and data access, and illustrate the scientific potential of our multi-band data. The data surpass the target depths originally planned for J-PAS, reaching $\rm{mag}_{\rm {AB}}$ between $\sim 22$ and $23.5$ for the NB filters and up to $24$ for the BB filters ($5\sigma$ in a $3$~arcsec aperture). The miniJPAS primary catalogue contains more than $64,000$ sources extracted in the $r$ detection band with forced photometry in all other bands. We estimate the catalogue to be complete up to $r=23.6$ for point-like sources and up to $r=22.7$ for extended sources. Photometric redshifts reach subpercent precision for all sources up to $r=22.5$, and a precision of $\sim 0.3$% for about half of the sample. (Abridged)


[16] 2007.01913

Infall of galaxies onto groups

Growth of the structure in the Universe manifest as accretion flows of galaxies onto groups and clusters. Thus, the present day properties of groups and their member galaxies are influenced by the characteristics of this continuous infall pattern. Several works both theoretical, in numerical simulations, and in observations, study this process and provide useful steps for a better understanding of galaxy systems and their evolution. We aim at exploring the streaming flow of galaxies onto groups using observational peculiar velocity data. The effects of distance uncertainties are also analyzed as well as the relation between the infall pattern and group and environment properties.This work deals with analysis of peculiar velocity data and their projection on the direction to group centers, to determine the mean galaxy infall flow. We applied this analysis to the galaxies and groups extracted from the Cosmicflows-3 catalog. We also use mock catalogs derived from numerical simulations to explore the effects of distance uncertainties on the derivation of the galaxy velocity flow onto groups. We determine the infalling velocity field onto galaxy groups with cz < 0.033 using peculiar velocity data. We measure the mean infall velocity onto group samples of different mass range, and also explore the impact of the environment where the group reside. Well beyond the group virial radius, the surrounding large-scale galaxy overdensity may impose additional infalling streaming amplitudes in the range 200 to 400 km s$^{-1}$. Also, we find that groups in samples with a well controlled galaxy density environment show an increasing infalling velocity amplitude with group mass, consistent with the predictions of the linear model. These results from observational data are in excellent agreement with those derived from the mock catalogs.


[17] 2007.01936

Probing Dark Low Mass Halos and Primordial Black Holes with Frequency Dependent Gravitational Lensing Dispersions of Gravitational Waves

We explore the possibility of using amplitude and phase fluctuations of gravitational waves due to gravitational lensing as a probe of the small-scale matter power spectrum. The direct measurement of the small-scale matter power spectrum is made possible by making use of the frequency dependence of such gravitational lensing dispersions originating from the wave optics nature of the propagation of gravitational waves. We first study the small-scale behavior of the matter power spectrum in detail taking the so-called halo model approach including effects of baryons and subhalos. We find that the matter power spectrum at the wavenumber $k\sim 10^6h{\rm Mpc}^{-1}$ is mainly determined by the abundance of dark low mass halos with mass $1h^{-1}M_\odot \lesssim M \lesssim 10^4h^{-1}M_\odot$ and is relatively insensitive to baryonic effects. The matter power spectrum at this wavenumber is probed by gravitational lensing dispersions of gravitational waves at frequencies of $f\sim 0.1-1$~Hz with predicted signals of $\mathcal{O}(10^{-3})$. We also find that Primordial Black Holes (PBHs) with $M_{\rm PBH} \gtrsim 0.1~M_\odot$ can significantly enhance the matter power spectrum at $k \gtrsim 10^5h{\rm Mpc}^{-1}$ due to both the enhanced halo formation and the shot noise from PBHs. We find that gravitational lensing dispersions at $f\sim 10-100$~Hz are particularly sensitive to PBHs and can be enhanced by more than an order of magnitude depending on the mass and abundance of PBHs.


[18] 2007.01976

On using dipolar modes to constrain the helium glitch in red-giant stars

The space-borne missions CoRoT and Kepler have revealed numerous mixed modes in red-giant stars. These modes carry a wealth of information about red-giant cores, but are of limited use when constraining rapid structural variations in their envelopes. This limitation can be circumvented if we have access to the frequencies of the pure acoustic dipolar modes in red giants, i.e. the dipole modes that would exist in the absence of coupling between gravity and acoustic waves. We present a pilot study aimed at evaluating the implications of using these pure acoustic mode frequencies in seismic studies of the helium structural variation in red giants. The study is based on artificial seismic data for a red-giant-branch stellar model, bracketing seven acoustic dipole radial orders around vmax. The pure acoustic dipole-mode frequencies are derived from a fit to the mixed-mode period spacings and then used to compute the pure acoustic dipole-mode second differences. The pure acoustic dipole-mode second differences inferred through this procedure follow the same oscillatory function as the radial modes second differences. The additional constraints brought by the dipolar modes allow us to adopt a more complete description of the glitch signature when performing the fit to the second differences. The amplitude of the glitch retrieved from this fit is 15% smaller than that from the fit based on the radial modes alone. Also, we find that thanks to the additional constraints, a bias in the inferred glitch location, found when adopting the simpler description of the glitch, is avoided.


[19] 2007.02012

Nonparametric galaxy morphology from UV to submm wavelengths

We present the first nonparametric morphological analysis of a set of spiral galaxies from UV to submm wavelengths. Our study is based on high-quality multi-wavelength imaging for nine well-resolved spiral galaxies from the DustPedia database, combined with nonparametric morphology indicators calculated in a consistent way using the {\tt{StatMorph}} package. We measure the half-light radius, the concentration index, the asymmetry index, the smoothness index, the Gini coefficient and the $M_{20}$ indicator in various wavebands from UV to submm wavelengths, as well as in stellar mass, dust mass and star formation rate maps. We find that the interstellar dust in galaxies is distributed in a more extended, less centrally concentrated, more asymmetric, and more clumpy way than the stars. This is particularly evident when comparing morphological indicators based on the stellar mass and dust mass maps. This should serve as a warning sign against treating the dust in galaxies as a simple smooth component. We argue that the nonparametric galaxy morphology of galaxies from UV to submm wavelengths is an interesting test for cosmological hydrodynamics simulations.


[20] 2007.02015

Time Evolution Of Cyclotron Line of Her X-1; A Detailed StatisticalAnalysis Including New ASTROSAT Data

The cyclotron line feature in the X-ray spectrum of the accretion powered pulsar Her X-1 has been observed and monitored for over three decades. The line energy exhibited a slow secular decline over the period 1995-2014, with a possible (not confirmed) indication of a reversal thereafter. Recent works have shown that the temporal evolution of the line energy may be modelled as a flattening after an earlier decrease until MJD 55400 ($\pm200)$. In this work, we present the results of ASTROSAT observations in the context of earlier data and offer a common interpretation through a detailed study of temporal and flux dependence. We find that the variation of the line energy does not support an upward trend but is consistent with the reported flattening after an earlier decrease until MJD $54487^{+515}_{-469}$.


[21] 2007.02051

The Pairing Probability of Massive Black Holes in Merger Galaxies in the Presence of Radiative Feedback

Dynamical friction (DF) against stars and gas is thought to be an important mechanism for orbital evolution of massive black holes (MBHs) in merger remnant galaxies. Recent theoretical investigations however show that DF does not always lead to MBH inspiral. For MBHs evolving in gas-rich backgrounds, the ionizing radiation that emerges from the innermost parts of their accretion flow can affect the surrounding gas in such a way to cause the MBHs to accelerate and gain orbital energy. This effect was dubbed ``negative DF". We use a semi-analytic model to study the impact of negative DF on pairs of MBHs in merger remnant galaxies evolving under the combined influence of stellar and gaseous DF. Our results show that for a wide range of merger galaxy and MBH properties negative DF reduces the MBH pairing probability by $\sim 40\%$. The suppression of MBH pairing is most severe in galaxies with one or more of these properties: (1) a gas fraction of $f_g \geq 0.2$; (2) a galactic gas disk rotating close to the circular velocity; (3) MBH pairs in prograde, low eccentricity orbits, and (4) MBH pairs with mass $< {\rm few}\times 10^7\,$M$_\odot$. The last point is of importance because MBH pairs in this mass range are direct progenitors of merging binaries targeted by the future space-based gravitational wave observatory LISA.


[22] 2007.02063

Limiting the impact of light pollution on human health, environment and stellar visibility

Light pollution is one of the most rapidly increasing types of environmental degradation. To limit this pollution several effective practices have been defined: shields on lighting fixtures to prevent direct upward light; no over lighting, i.e. avoid using higher lighting levels than strictly needed for the task, constraining illumination to the area where and when it is needed. Nevertheless, even after the best control of the light distribution is reached and when the proper quantity of light is used, upward light emission remains, due to reflections from the lit surfaces and atmospheric scatter. The environmental impact of this "residual light pollution" cannot be neglected and should be limited too. We propose a new way to limit the effects of this residual light pollution on wildlife, human health and stellar visibility. We performed analysis of the spectra of common types of lamps for external use, including the new LEDs. We evaluated their emissions relative to the spectral response functions of human eye photoreceptors, in the photopic, scotopic and melatonin suppressing bands finding that the amount of pollution is strongly dependent on the spectral characteristics of the lamps, with the more environmentally friendly lamps being low pressure sodium, followed by high pressure sodium. Most polluting are the lamps with a strong blue emission, like white LEDs. Migration from the now widely used sodium lamps to white lamps (Metal Halide and LEDs) would produce an increase of pollution in the scotopic and melatonin suppression bands of more than five times the present levels, supposing the same photopic installed flux. This increase will exacerbate known and possible unknown effects of light pollution on human health, environment and on starry sky visibility. We present quantitative criteria to evaluate the lamps based on their spectral emissions and we suggest regulatory limits.


[23] 2007.02101

Nickel clumps and light curve bumps: Light curves and spectra of models with macroscopic $^{56}$Ni clumps in the outer ejecta

An excess of flux in the early light curves of type Ia supernovae has been observed in a few cases. Multiple scenarios have been proposed to explain this. Recently, it has been shown that for at least one object (SN$~$2018oh) the excess emission observed could be the result of a large-scale clump of $^{56}$Ni in the outer ejecta of $\sim$0.03$~M_{\rm{\odot}}$. We present model light curves and spectra for ejecta profiles containing $^{56}$Ni clumps of varying masses (0.01, 0.02, 0.03, and 0.04$~M_{\rm{\odot}}$) and shapes. We find that even for our lowest mass $^{56}$Ni clump, an increase of $\gtrsim$2 magnitudes is produced in the bolometric light curve at one day after explosion, relative to models without a $^{56}$Ni clump. We show that the colour evolution of models with a $^{56}$Ni clump differs significantly from those without, and shows a colour inversion similar to some double-detonation explosion models. Furthermore, spectra of our $^{56}$Ni clump models show that strong suppression of flux between $\sim$3$~$700 $-$ 4$~$000$~$Ang. close to maximum light appears to be a generic feature for this class of model. Comparing our models to observations of SNe$~$2017cbv and 2018oh, we show that a $^{56}$Ni clump of 0.02 $-$ 0.04$~M_{\rm{\odot}}$ can match shapes of the early light curve bumps, however the colour and spectral evolution are in disagreement. This would indicate that an alternative origin for the flux excess is necessary. In addition, based on existing explosion scenarios, producing a large-scale, macroscopic $^{56}$Ni clump in the outer ejecta as required to match the light curve shape, without the presence of additional short-lived radioactive material, may prove challenging. Given that only a small amount of $^{56}$Ni in the outer ejecta is required to produce a bump in the light curve, such a large clump in the outer ejecta must be rare, if it were to occur at all.


[24] 2007.02120

Gas and dust from metal-rich AGB stars

Context: Stars evolving through the asymptotic giant branch (AGB) phase provide significant feedback to their host system, in form of both gas enriched in nuclear-burning products and dust formed in their winds, which they eject into the interstellar medium. Therefore AGB stars are an essential ingredient for the chemical evolution of the Milky Way and other galaxies. Aims: We study AGB models with super-solar metallicity, to complete our large database, so far extending from metal-poor to solar chemical compositions. We provide chemical yields for masses in the range 1-8 Msun and metallicities Z=0.03 and Z=0.04. We also study dust production in this metallicity domain. Methods: We calculated the evolutionary sequences from the pre main sequence through the whole AGB phase. We follow the variation of the surface chemical composition to calculate the chemical yields of the various species and model dust formation in the winds to determine the dust production rate and the total dust mass produced by each star during the AGB phase. Results: The physical and chemical evolution of the star is sensitive to the initial mass: M> 3Msun stars experience hot bottom burning, whereas the surface chemistry of the lower mass counterparts is altered only by third dredge-up. The carbon-star phase is reached by 2.5-3.5Msun stars of metallicity Z=0.03, whereas all the Z=0.04 stars (except the 2.5 Msun) remain O-rich for the whole AGB phase. Most of the dust produced by metal-rich AGBs is in the form of silicates particles. The total mass of dust produced increases with the mass of the star, reaching ~ 0.012 Msun for 8Msun stars.


[25] 2007.02122

ExoMol line lists -- XXXIX. Ro-vibrational molecular line list for CO$_2$

A new hot line list for the main isotopologue of CO$_2$ is presented. The line list consists of almost 2.5 billion transitions between 3.5 million rotation-vibration states of CO$_2$ in its ground electronic state, covering the wavenumber range 0-20000 cm$^{-1}$ ($\lambda >0.5$ $\mu$m) with the upper and lower energy thresholds of 36 000 cm$^{-1}$ and 16 000 cm$^{-1}$, respectively. The ro-vibrational energies and wavefunctions are computed variationally using the Ames-2 accurate empirical potential energy surface. The ro-vibrational transition probabilities in the form of Einstein coefficients are computed using an accurate ab initio dipole moment surface using variational program TROVE. A new implementation of TROVE which uses an exact nuclear-motion kinetic energy operator is employed. Comparisons with the existing hot line lists are presented. The line list should be useful for atmospheric retrievals of exoplanets and cool stars. The UCL-4000 line list is available from the CDS and ExoMol databases.


[26] 2007.02148

The flux-weighted gravity-luminosity relation of Galactic classical Cepheids

The flux-weighted gravity-luminosity relation (FWGLR) is investigated for a sample of 477 classical Cepheids (CCs), including stars that have been classified in the literature as such but are probably not. The luminosities are taken from the literature, based on the fitting of the spectral energy distributions (SEDs) assuming a certain distance and reddening. The flux-weighted gravity (FWG) is taken from gravity and effective temperature determinations in the literature based on high-resolution spectroscopy. There is a very good agreement between the theoretically predicted and observed FWG versus pulsation period relation that could serve in estimating the FWG (and $\log g$) in spectroscopic studies with a precision of 0.1~dex. As was known in the literature, the theoretically predicted FWGLR relation for CCs is very tight and is not very sensitive to metallicity (at least for LMC and solar values), rotation rate, and crossing of the instability strip. The observed relation has a slightly different slope and shows more scatter (0.54~dex). This is due both to uncertainties in the distances and to the pulsation phase averaged FWG values. Data from future Gaia data releases should reduce these errors, and then the FWGLR could serve as a powerful tool in Cepheid studies.


[27] 2007.02155

A Distant Fast Radio Burst Associated to its Host Galaxy with the Very Large Array

We present the discovery and subarcsecond localization of a new Fast Radio Burst with the Karl G. Jansky Very Large Array and realfast search system. The FRB was discovered on 2019 June 14 with a dispersion measure of 959 pc/cm3. This is the highest DM of any localized FRB and its measured burst fluence of 0.6 Jy ms is less than nearly all other FRBs. The source is not detected to repeat in 15 hours of VLA observing and 153 hours of CHIME/FRB observing. We describe a suite of statistical and data quality tests we used to verify the significance of the event and its localization precision. Follow-up optical/infrared photometry with Keck and Gemini associate the FRB to a pair of galaxies with $\rm{r}\sim23$ mag. The false-alarm rate for radio transients of this significance that are associated with a host galaxy is roughly $3\times10^{-4}\ \rm{hr}^{-1}$. The two putative host galaxies have similar photometric redshifts of $z_{\rm{phot}}\sim0.6$, but different colors and stellar masses. Comparing the host distance to that implied by the dispersion measure suggests a modest (~ 50 pc/cm3) electron column density associated with the FRB environment or host galaxy/galaxies.


[28] 2007.02170

Solar-Like Oscillations: Lessons Learned & First Results from TESS

Solar-like oscillations are excited in cool stars with convective envelopes and provide a powerful tool to constrain fundamental stellar properties and interior physics. We provide a brief history of the detection of solar-like oscillations, focusing in particular on the space-based photometry revolution started by the CoRoT and Kepler Missions. We then discuss some of the lessons learned from these missions, and highlight the continued importance of smaller space telescopes such as BRITE constellation to characterize very bright stars with independent observational constraints. As an example, we use BRITE observations to measure a tentative surface rotation period of 28.3+/-0.5 days for alpha Cen A, which has so far been poorly constrained. We also discuss the expected yields of solar-like oscillators from the TESS Mission, demonstrating that TESS will complement Kepler by discovering oscillations in a large number of nearby subgiants, and present first detections of oscillations in TESS exoplanet host stars.


[29] 2007.02181

High Precision Calibration Pairs for Southern Lucky Imaging

Accurate measures of double stars require accurate calibration of the instrument. Here we present a list of 50 pairs, that are quasi-evenly spaced over the southern sky, and that have Separations and Position Angles accurate at the milli-arcsec, and milli-degree level. These wide angle pairs are suggested as calibration pairs for lucky imaging observations.


[30] 2007.02184

Modeling of Galactic Foreground Polarization with Velocity Gradients

The detection of primordial B-mode polarization is still challenging due to the relatively low amplitude compared to the galactic foregrounds. To remove the contribution from the foreground, a comprehensive picture of the galactic magnetic field is indispensable. The Velocity Gradient Technique (VGT) is promising in tracing magnetic fields based on the modern understanding of the magneto-hydrodynamic turbulence. In this work, we apply VGT to a HI region containing an intermediate velocity cloud and a local velocity cloud, which are distinguishable in position-position-velocity space. We show that VGT gives an excellent agreement with the Planck polarization and stellar polarization. We confirm the advantages of VGT in constructing the 3D galactic magnetic field.


[31] 2007.02207

Multiplexing lobster-eye optics: a concept for wide-field X-ray monitoring

We propose a concept of multiplexing lobster-eye (MuLE) optics to achieve significant reductions in the number of focal plane imagers in lobster-eye (LE) wide-field X-ray monitors. In the MuLE configuration, an LE mirror is divided into several segments and the X-rays reflected on each of these segments are focused on a single image sensor in a multiplexed configuration. If each LE segment assumes a different rotation angle, the azimuthal rotation angle of a cross-like image reconstructed from a point source by the LE optics identifies the specific segment that focuses the X-rays on the imager. With a focal length of 30 cm and LE segments with areas of 10 x 10 cm^2, ~1 sr of the sky can be covered with 36 LE segments and only four imagers (with total areas of 10 x 10 cm^2). A ray tracing simulation was performed to evaluate the nine-segment MuLE configuration. The simulation showed that the flux (0.5 to 2 keV) associated with the 5-sigma detection limit was ~2 x 10^-10 erg cm^-2 s^-1 (10 mCrab) for a transient with a duration of 100 s. The simulation also showed that the direction of the transient for flux in the range of 14 to 17 mCrab at 0.6 keV was determined correctly with 99.7% confidence limit. We conclude that the MuLE configuration can become an effective on-board device for small satellites for future X-ray wide-field transient monitoring.


[32] 2007.02213

Constraining Primordial Black Holes with Dwarf Galaxy Heating

Black holes formed in the early universe, prior to the formation of stars, can exist as dark matter and also contribute to the black hole merger events observed in gravitational waves. We set a new limit on the abundance of primordial black holes (PBHs) by considering interactions of PBHs with the interstellar medium, which result in the heating of gas. We examine generic heating mechanisms, including emission from the accretion disk, dynamical friction, and disk outflows. Using the data from the Leo T dwarf galaxy, we set a new cosmology-independent limit on the abundance of PBHs in the mass range $\mathcal{O}(1) M_{\odot}-10^7 M_{\odot}$.


[33] 2007.02241

K-band spectra of selected post-AGB candidates

We present medium resolution (1000) K-band spectra of 12 post-AGB candidates and related stars. For several objects in our sample, these spectra were obtained for the first time. The Br$\gamma$ line in emission is detected in seven objects indicating the onset of photo-ionization in these objects. Four objects show the presence of He i line. We detect H2 emission line in the spectra of IRAS 06556+1623, IRAS 22023+5249, IRAS 18062+2410 and IRAS 20462+3416. H2 emission line ratio 1-0 S(1)/2-1 S(1) indicate that H2 is radiatively excited due to the UV radiation of hot post-AGB central stars. When compared with the recent observations by other investigators, the Br$\gamma$ and H2 emission fluxes varied in some of the objects. The hot post-AGB stars IRAS 22495+5134, IRAS 22023+5249, IRAS 18062+2410 and IRAS 20462+3416 seem to be evolving rapidly to young low excitation planetary nebula phase. The spectra of the objects presented in this paper may be useful for future observers as some of these stars show spectral variation and since the post-AGB evolution of some of these stars is relatively rapid.


[34] 2007.02243

Radiative-transfer modeling of nebular-phase type II supernovae. Dependencies on progenitor and explosion properties

Nebular phase spectra of core-collapse supernovae (SNe) provide critical and unique information on the progenitor massive star and its explosion. We present a set of 1-D steady-state non-local thermodynamic equilibrium radiative transfer calculations of type II SNe at 300d after explosion. Guided by results for a large set of stellar evolution simulations, we craft ejecta models for type II SNe from the explosion of a 12, 15, 20, and 25Msun star. The ejecta density structure and kinetic energy, the 56Ni mass, and the level of chemical mixing are parametrized. Our model spectra are sensitive to the adopted line Doppler width, a phenomenon we associate with the overlap of FeII and OI lines with Lyalpha and Lybeta. Our spectra show a strong sensitivity to 56Ni mixing since it determines where decay power is absorbed. Even at 300d after explosion, the H-rich layers reprocess the radiation from the inner metal rich layers. In a given progenitor model, variations in 56Ni mass and distribution impact the ejecta ionization, which can modulate the strength of all lines. Such ionization shifts can quench CaII line emission. In our set of models, the OI6300 doublet strength is the most robust signature of progenitor mass. However, we emphasize that convective shell merging in the progenitor massive star interior can pollute the O-rich shell with Ca, which will weaken the OI6300 doublet flux in the resulting nebular SN II spectrum. This process may occur in Nature, with a greater occurrence in higher mass progenitors, and may explain in part the preponderance of progenitor masses below 17Msun inferred from nebular spectra.


[35] 2007.02276

Probing axion dark matter with 21cm fluctuations from minihalos

If the symmetry breaking inducing the axion occurs after the inflation, the large axion isocurvature perturbations can arise due to a different axion amplitude in each causally disconnected patch. This causes the enhancement of the small-scale density fluctuations which can significantly affect the evolution of structure formation. The epoch of the small halo formation becomes earlier and we estimate the abundance of those minihalos which can host the neutral hydrogen atoms to result in the 21cm fluctuation signals. We find that the future radio telescopes, such as the SKA, can put the axion mass bound of order $m_a \gtrsim 10^{-13}$ eV for the simple temperature-independent axion mass model, and the bound can be extended to of order $m_a \gtrsim 10^{-8}$eV for a temperature-dependent axion mass.


[36] 2007.02292

Effects of observer peculiar motion on the isotropic background frequency spectrum: from monopole to higher multipoles

The observer peculiar motion produces boosting effects in the anisotropy pattern of the background with frequency spectral behaviours related to its spectrum. We study how the spectral behaviour of the background isotropic monopole emission is transferred to the frequency spectra at higher multipoles, l. We perform the analysis in terms of spherical harmonic expansion up to a certain lmax, for various background models from radio to far-IR. We derive a system of linear equations to obtain spherical harmonic coefficients and provide explicit solutions up to lmax=6 as linear combinations of the signals at N=lmax+1 colatitudes. Using the symmetry of associated Legendre polynomials with respect to {\pi}/2 the system can be separated into two subsystems, one for l=0 and even l, the other for odd l. This improves the solutions accuracy with respect to an arbitrary colatitudes choice. We apply the method to various types of monopole spectra represented by analytical or semi-analytical functions, i.e. to four types of CMB distorted spectra, four types of extragalactic backgrounds superimposed to the CMB Planckian spectrum and some combinations of them. We present our results in terms of spherical harmonic coefficients, relationships between the observed and intrinsic monopole spectra, maps and angular power spectra. We compare the method results with the ones obtained using more computationally demanding numerical integrations or map generation/inversion. The simplicity and efficiency of the method can significantly alleviate the computational effort needed for accurate predictions and for the analysis of data from future projects. We discuss the superposition of the CMB intrinsic anisotropies and of the effects induced by the observer motion, exploring for the possibility of constraining the intrinsic dipole embedded in the kinematic dipole, in the presence of CMB spectral distortions.


[37] 2007.02321

Accurate and Efficient Propagation of Satellite Orbits in the Terrestrial Gravity Field

Fast and precise propagation of satellite orbits is required for mission design, orbit determination in support of operations and payload data analysis. This demand must also comply with the different accuracy requirements set by a growing variety of scientific and service missions. This contribution proposes a method to improve the computational performance of orbit propagators through an efficient numerical integration that meets the accuracy requirements set by the specific application. This is achieved by appropriately tuning the parameters of the numerical propagator (relative tolerance and maximum time step), establishing a threshold for the perturbing accelerations (Earth's gravitational potential, atmospheric drag, solar radiation pressure, third-body perturbations, relativistic correction to gravity) below which they can be neglected without altering the quality of the results and implementing an efficient and precise algorithm for the harmonic synthesis of the geo-potential and its first-order gradient. In particular, when performing the harmonic synthesis, the number of spherical harmonics to retain (i.e., the expansion degree) is determined by the accuracy requirement. Given that higher-order harmonics decay rapidly with altitude, the expansion degree necessary to meet the target accuracy decreases with height. To improve the computational efficiency, the number of degrees to retain is determined dynamically while the trajectory is being computed. The optimum expansion degree for each altitude is determined by ensuring that the truncation error of the harmonic synthesis is below the threshold acceleration. The work is a generalization to arbitrary orbits of a previous study that focused on communication satellites in geosynchronous inclined orbits. The method is presented and a set of test cases is analysed and discussed.


[38] 2007.02322

A Monte Carlo Implementation of Galactic Free-Free Emission for the EoR Foreground Models

The overwhelming foreground causes severe contamination on the detection of 21-cm signal during the Epoch of Reionization (EoR). Among various foreground components, the Galactic free-free emission is less studied, so that its impact on the EoR observation remains unclear. To better constrain this emission, we perform the Monte Carlo simulation of H$\alpha$ emission, which comprises direct and scattered H$\alpha$ radiation from HII regions and warm ionized medium (WIM). The positions and radii of HII regions are quoted from the WISE HII catalog, and the WIM is described by an axisymmetric model. The scattering is off dust and free electrons that are realized by applying an exponential fitting to the HI4PI HI map and an exponential disk model, respectively. The simulated H$\alpha$ intensity, the Simfast21 software, and the latest SKA1-Low layout configuration are employed to simulate the SKA "observed" images of Galactic free-free emission and the EoR signal. By analyzing the one-dimensional power spectra, we find that the Galactic free-free emission can be about $10^{5.4}$-$10^{2.1}$, $10^{5.0}$-$10^{1.7}$, and $10^{4.3}$-$10^{1.1}$ times more luminous than the EoR signal on scales of $0.1~{\rm Mpc^{-1}} < k < 2~{\rm Mpc^{-1}}$ in the 116-124, 146-154, and 186-194 MHz frequency bands, respectively. We further calculate the two-dimensional power spectra inside the EoR window and show that the power leaked by Galactic free-free emission can still be significant, as the power ratios can reach about $110\%$-$8000\%$, $30\%$-$2400\%$, and $10\%$-$250\%$ on scales of $0.5~{\rm Mpc^{-1}} \lesssim k \lesssim 1~{\rm Mpc^{-1}}$ in three frequency bands. Therefore, we indicate that the Galactic free-free emission should be carefully treated in future EoR detections.


[39] 2007.02347

VLBI20-30: a scientific roadmap for the next decade -- The future of the European VLBI Network

This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and provides suggestions towards upgrade paths for the European VLBI Network (EVN). The EVN is a distributed long-baseline radio interferometric array, that operates at the very forefront of astronomical research. Recent results, together with the new science possibilities outlined in this vision document, demonstrate the EVN's potential to generate new and exciting results that will transform our view of the cosmos. Together with e-MERLIN, the EVN provides a range of baseline lengths that permit unique studies of faint radio sources to be made over a wide range of spatial scales. The science cases are reviewed in six chapters that cover the following broad areas: cosmology, galaxy formation and evolution, innermost regions of active galactic nuclei, explosive phenomena and transients, stars and stellar masers in the Milky Way, celestial reference frames and space applications. The document concludes with identifying the synergies with other radio, as well as multi-band/multi-messenger instruments, and provide the recommendations for future improvements. The appendices briefly describe other radio VLBI arrays, the technological framework for EVN developments, and a selection of spectral lines of astrophysical interest below 100 GHz. The document includes a glossary for non-specialists, and a list of acronyms at the end.


[40] 2007.02350

Orbits of 47 Dwarf Satellite Galaxies of the Milky Way in Three Models of the Gravitational Potential with Different Masses

The analysis of the orbits of 47 dwarf satellite galaxies of the Milky Way, built using three models of the Galactic gravitational potential with different masses, is presented. The models of the Galactic potential were chosen based on the analysis of a large number of the Galaxy mass estimates known from the literature. The astrometric data needed for calculation of the initial positions and velocities (6D phase space) of the dwarf galaxies are also taken from the literature, where the average proper motions were determined on the basis of the data from the Gaia DR2 Catalog. We present the orbits and their properties of all 47 dwarf galaxies obtained by integration for 13.5 Gyr backward in all three models of the Galactic potential and give a comparison of the orbital parameters. For each model of the Galactic potential we have identified dwarf galaxies that are not connected gravitationally with the Milky Way.


[41] 2007.02400

On the true fractions of repeating and non-repeating FRB sources

Observationally, fast radio bursts (FRBs) can be divided into repeating and apparently non-repeating (one-off) ones. It is unclear whether all FRBs repeat and whether there are genuine non-repeating FRBs. We attempt to address these questions using Monte Carlo simulations. We define a parameter $T_c$ at which the accumulated number of non-repeating sources becomes comparable to the total number of the repeating sources, which is a good proxy to denote the intrinsic repeater fraction among FRBs. Assuming that both types of sources exist, we investigate how the {\em observed} repeater fraction evolves with time for different parameters, including $T_c$, the repeating rate distribution power-law index $q$, the minimum repetition rate $r_{\rm 0,min}$, as well as the Weibull distribution index $k$ for repeating bursts. We find that unless $T_c \rightarrow \infty$ (i.e. there is no genuine non-repeating FRB source), the observed repeater fraction should increase with time first, reaching a peak, and then declines. The peak time $T_p$ and the peak fraction $F_{\rm r,obs,p}$ depend on $T_c$ and other repeating rate parameters. With the current data, one may pose a lower limit $T_c > (0.5-25)$ d for reasonable parameter values. Future continuous monitoring of FRBs using wide-field radio telescopes such as CHIME would measure or set a more stringent lower limit on $T_c$. The detection of a peak in the observed repeater fraction would disfavor the ansatz that ``all FRB sources repeat''.


[42] 2007.02402

Dust Reverberation Mapping in Distant Quasars from Optical and Mid-Infrared Imaging Surveys

The size of the dust torus in Active Galactic Nuclei (AGN) and their high-luminosity counterparts, quasars, can be inferred from the time delay between UV/optical accretion disk continuum variability and the response in the mid-infrared (MIR) torus emission. This dust reverberation mapping (RM) technique has been successfully applied to $\sim 70$ $z\lesssim 0.3$ AGN and quasars. Here we present first results of our dust RM program for distant quasars covered in the SDSS Stripe 82 region combining $\sim 20$-yr ground-based optical light curves with 10-yr MIR light curves from the WISE satellite. We measure a high-fidelity lag between W1-band (3.4 $\mu$m) and $g$ band for 587 quasars over $0.3\lesssim z\lesssim 2$ ($\left<z\right>\sim 0.8$) and two orders of magnitude in quasar luminosity. They tightly follow (intrinsic scatter $\sim 0.17$ dex in lag) the IR lag-luminosity relation observed for $z<0.3$ AGN, revealing a remarkable size-luminosity relation for the dust torus over more than four decades in AGN luminosity, with little dependence on additional quasar properties such as Eddington ratio and variability amplitude. This study motivates further investigations in the utility of dust RM for cosmology, and strongly endorses a compelling science case for the combined 10-yr Vera C. Rubin Observatory Legacy Survey of Space and Time (optical) and 5-yr Nancy Grace Roman Space Telescope 2$\mu$m light curves in a deep survey for low-redshift AGN dust RM with much lower luminosities and shorter, measurable IR lags. The compiled optical and MIR light curves for 7,384 quasars in our parent sample are made public with this work.


[43] 2007.02406

Modeling of extended atmospheres with temperatures below 40000K

We calculate models of extended stellar atmospheres with a temperature in the range of 12000-40000K and a mass loss rate of $10^{-6}-10^{-4} M_{\odot}$ yr$^{-1}$. A large number of objects with emission spectra, such as luminous blue variables (LBV), FeII - emission line stars, Of/late-WN stars, and even ultraluminous X-ray sources (ULXs) often have effective temperatures in this range. The paper presents the results of model grids calculating in the form of equivalent width diagrams for the selected lines of hydrogen, He, Si, and Fe, as well as the results of studies of some emission objects using the calculated models.


[44] 2007.02420

High-resolution Spectra for a Wide Range of Habitable Zone Planets around Sun-like Stars

The search for life in the universe is currently focused on Earth-analog planets. However, we should be prepared to find a diversity of terrestrial exoplanets not only in terms of host star but also in terms of surface environment. Simulated high-resolution spectra of habitable planets covering a wide parameter space are essential in training retrieval tools, optimizing observing strategies, and interpreting upcoming observations. Ground-based extremely large telescopes like ELT, GMT, and TMT; and future space-based mission concepts like Origins, HabEx, and LUVOIR are designed to have the capability of characterizing a variety of potentially habitable worlds. Some of these telescopes will use high precision radial velocity techniques to obtain the required high-resolution spectra ($R\approx100,000$) needed to characterize potentially habitable exoplanets. Here we present a database of high-resolution (0.01 cm$^{-1}$) reflection and emission spectra for simulated exoplanets with a wide range of surfaces, receiving similar irradiation as Earth around 12 different host stars from F0 to K7. Depending on surface type and host star, we show differences in spectral feature strength as well as overall reflectance, emission, and star to planet contrast ratio of terrestrial planets in the Habitable zone of their host stars. Accounting for the wavelength-dependent interaction of the stellar flux and the surface will help identify the best targets for upcoming spectral observations in the visible and infrared. All of our spectra and model profiles are available online.


[45] 2007.02425

Machine learning as a flaring storm warning machine: Was a warning machine for the September 2017 solar flaring storm possible?

Machine learning is nowadays the methodology of choice for flare forecasting and supervised techniques, in both their traditional and deep versions, are becoming the most frequently used ones for prediction in this area of space weather. Yet, machine learning has not been able so far to realize an operating warning system for flaring storms and the scientific literature of the last decade suggests that its performances in the prediction of intense solar flares are not optimal. The main difficulties related to forecasting solar flaring storms are probably two. First, most methods are conceived to provide probabilistic predictions and not to send binary yes/no indications on the consecutive occurrence of flares along an extended time range. Second, flaring storms are typically characterized by the explosion of high energy events, which are seldom recorded in the databases of space missions; as a consequence, supervised methods are trained on very imbalanced historical sets, which makes them particularly ineffective for the forecasting of intense flares. Yet, in this study we show that supervised machine learning could be utilized in a way to send timely warnings about the most violent and most unexpected flaring event of the last decade, and even to predict with some accuracy the energy budget daily released by magnetic reconnection during the whole time course of the storm. Further, we show that the combination of sparsity-enhancing machine learning and feature ranking could allow the identification of the prominent role that energy played as an Active Region property in the forecasting process.


[46] 2007.02444

Reduction of optical crosstalk in SiPMs due to coupled light guides and investigation of other properties demonstrated with the SensL MicroFJ-60035-TSV

During the past decade, semi-conductor photo sensors have replaced photo multiplier tubes in numerous applications featuring single-photon resolution, insensitivity to magnetic fields, higher robustness and enhanced photo detection efficiency at lower operation voltage and lower costs. This paper presents a measurement of gain, optical crosstalk and dark count rate of 127 Silicon Photo Multipliers (SiPMs) of type SensL MicroFJ-60035-TSV at nominal bias voltage. In SiPMs, optical crosstalk can fake higher multiplicities for single-photon hits. This paper demonstrates that optically coupled light guides reduce this probability significantly. The measured sensors offer a comparably small variation of their breakdown voltage with temperature of only $21.5\,\mathrm{mV/K}$. The manufacturer specifies a limited range of only $\pm 250\,\mathrm{mV/K}$ for their nominal breakdown voltage. This should allow for operation with small systematic errors without major efforts on temperature-based bias voltage compensation and without calibration of their individual breakdown voltages. This paper proves that the gain distribution of the measured sensors is consistent with the data sheet values.


[47] 2007.02458

Evaluating the Calibration of SN Ia Anchor Datasets with a Bayesian Hierarchical Model

Inter-survey calibration remains an important systematic uncertainty in cosmological studies using type Ia supernova (SNe Ia). Ideally, each survey would measure its system throughputs, for instance with bandpass measurements combined with observations of well-characterized spectrophotometric standard stars; however, many important nearby-SN surveys have not done this. We recalibrate these surveys by tying their tertiary survey stars to Pan-STARRS1 g, r, and i, and SDSS/CSP u. This improves upon previous recalibration efforts by taking the spatially variable zeropoints of each telescope/camera into account, and applying improved color transformations in the surveys' natural instrumental photometric systems. Our analysis uses a global hierarchical model of the data which produces a covariance matrix of magnitude offsets and bandpass shifts, quantifying and reducing the systematic uncertainties in the calibration. We call our method CROSS-CALIBration with a Uniform Reanalysis (X-CALIBUR). This approach gains not only from a sophisticated analysis, but also from simply tying our calibration to more color calibrators, rather than just the one color calibrator (BD+17 4708) as many previous efforts have done. The results presented here have the potential to help understand and improve calibration uncertainties upcoming SN Ia cosmological analyses.


[48] 2007.02493

The $-12$ mag dip in the galaxy luminosity function of Hickson Compact Groups

We present the galaxy luminosity functions (LFs) of four Hickson Compact Groups using image data from the Subaru Hyper Suprime-Cam. A distinct dip appeared in the faint-ends of all the LFs at $M_g\sim-12$. A similar dip was observed in the LFs of the galaxy clusters Coma and Centaurus. However, LFs in the Virgo, Hydra, and the field had flatter slopes and no dips. As the relative velocities among galaxies are lower in compact groups than in clusters, the effect of galaxy-galaxy interactions would be more significant in compact groups. The $M_g\sim-12$ dip of compact groups may imply that frequent galaxy-galaxy interactions would affect the evolution of galaxies, and the dip in LF could become a boundary between different galaxy populations.


[49] 2007.02513

GW190814's secondary component with mass $(2.50-2.67)$ M$_{\odot}$ as a super-fast pulsar

Using Stergioulas's RNS code for investigating fast pulsars with Equation of States (EOSs) on the causality surface (where the speed of sound equals to that of light) of the high-density EOS parameter space satisfying all known constraints from both nuclear physics and astrophysics, we show that the GW190814's secondary component of mass $(2.50-2.67)$ M$_{\odot}$ can be a super-fast pulsar spinning faster than 971 Hz about 42\% below its Kepler frequency. There is a large and physically allowed EOS parameter space below the causality surface where pulsars heavier than 2.50 M$_{\odot}$ are supported if they can rotate even faster with critical frequencies depending strongly on the high-density behavior of nuclear symmetry energy.


[50] 2007.02525

Photoionization modelling of quiescence phase spectra of novae & symbiotic star

We present results of study, using observed and published spectra in optical region, of few novae (T CrB, GK Per, RS Oph, V3890 Sgr and V745 Sco) in their quiescence phase and a symbiotic star (BX Mon). Observations were made using the facilities available at 2m Himalayan Chandra Telescope (HCT). Generally, the spectra show prominent low ionization emission features of hydrogen, helium, iron and oxygen and TiO absorption features due to the cool secondary component; T CrB and GK Per show higher ionization lines. We used photoionization code CLOUDY to model these spectra. From the best-fit models, we have estimated the physical parameters, e.g., temperature, luminosity & hydrogen density; estimated elemental abundances and other parameters related to the system. By matching the spectra of various giants with the absorption features and from the best-fit, we determined the type of secondaries and also their contribution to the spectra.


[51] 2007.02528

Triaxially-deformed Freely-precessing Neutron Stars: Continuous electromagnetic and gravitational radiation

The shape of a neutron star (NS) is closely linked to its internal structure and the equation of state of supranuclear matters. A rapidly rotating, asymmetric NS in the Milky Way undergoes free precession, making it a potential source for multimessenger observation. The free precession could manifest in (i) the spectra of continuous gravitational waves (GWs) in the kilohertz band for ground-based GW detectors, and (ii) the timing behavior and pulse-profile characteristics if the NS is monitored as a pulsar with radio and/or X-ray telescopes. We extend previous work and investigate in great detail the free precession of a triaxially deformed NS with analytical and numerical approaches. In particular, its associated continuous GWs and pulse signals are derived. Explicit examples are illustrated for the continuous GWs, as well as timing residuals in both time and frequency domains. These results are ready to be used for future multimessenger observation of triaxially-deformed freely-precessing NSs, in order to extract scientific implication as much as possible.


[52] 2007.02539

General solution for the vacuum electromagnetic field in the surroundings of a rotating star

Aims. Many recent observations of pulsars and magnetars can be interpreted in terms of neutron stars (NS) with multipole electromagnetic fields. As a first approximation, we investigate the multipole magnetic and electric fields in the environment of a rotating star when this environment is deprived of plasma. Methods. We compute a multipole expansion of the electromagnetic field in vacuum for a given magnetic field on the conducting surface of the rotating star. Then, we consider a few consequences of multipole fields of pulsars. Results. We provide an explicit form of the solution. For each spherical harmonic of the magnetic field, the expansion contains a finite number of terms. A multipole magnetic field can provide an explanation for the stable sub-structures of pulses, and they offer a solution to the problem of current closure in pulsar magnetospheres. Conclusions. This computation generalises the widely used model of a rotating star in vacuum with a dipole field. It can be especially useful as a first approximation to the electromagnetic environment of a compact star, for instance a neutron star, with an arbitrarily magnetic field.


[53] 2007.02551

Collision of Merger and Accretion Shocks: Formation of Mpc-scale Contact Discontinuity in the Perseus Cluster

Two Mpc-size contact discontinuities have recently been identified in the XMM-Newton and Suzaku X-ray observations of the outskirts of the Perseus cluster (Walker et al. 2020). These structures have been tentatively interpreted as "sloshing cold fronts", which are customarily associated with differential motions of the cluster gas perturbed by a merger. In this study we consider an alternative scenario, namely, that the most prominent discontinuity near the cluster virial radius is the result of the collision between the accretion shock and the "runaway" merger shock. We also discuss the possible origin of the second discontinuity at ~1.2 Mpc.


[54] 2007.02560

Hurricanes on Tidally Locked Terrestrial Planets: Fixed SST Experiments

Are there hurricanes on exoplanets? Tidally locked terrestrial planets around M dwarfs are the main targets of space missions for finding habitable exoplanets. Whether hurricanes can form on this kind of planet is important for their climate and habitability. Using a high-resolution global atmospheric circulation model, we investigate whether there are hurricanes on tidally locked terrestrial planets under fixed sea surface temperatures (SST). The effects of planetary rotation rate, surface temperature, and bulk atmospheric compositions are examined. We find that hurricanes can form on the planets but not on all of them. For planets near the inner edge of the habitable zone of late M dwarfs, there are more and stronger hurricanes on both day and night sides. For planets in the middle and outer ranges of the habitable zone, the possibility of hurricane formation is low or even close to zero, as suggested in the study of Bin et al.(2017). Hurricane theories on Earth are applicable to tidally locked planets when atmospheric compositions are similar to Earth. However, if background atmosphere is lighter than H2O, hurricanes can hardly be produced because convection is always inhibited due to the effect of mean molecular weight, similar to that on Saturn. These results have broad implications on the precipitation, ocean mixing, climate, and atmospheric characterization of tidally locked planets. Finally, A test with a coupled slab ocean and an earth-like atmosphere in a tide-locked orbit of 10 earth days shows that there are also hurricanes in the experiment.


[55] 2007.02564

Reliable Probability Forecast of Solar Flares: Deep Flare Net-Reliable (DeFN-R)

We developed a reliable probabilistic solar flare forecasting model using a deep neural network, named Deep Flare Net-Reliable (DeFN-R). The model can predict the maximum classes of flares that occur in the following 24 h after observing images, along with the event occurrence probability. We detected active regions from 3x10^5 solar images taken during 2010-2015 by Solar Dynamic Observatory and extracted 79 features for each region, which we annotated with flare occurrence labels of X-, M-, and C-classes. The extracted features are the same as used by Nishizuka et al. (2018); for example, line-of-sight/vector magnetograms in the photosphere, brightening in the corona, and the X-ray emissivity 1 and 2 h before an image. We adopted a chronological split of the database into two for training and testing in an operational setting: the dataset in 2010-2014 for training and the one in 2015 for testing. DeFN-R is composed of multilayer perceptrons formed by batch normalizations and skip connections. By tuning optimization methods, DeFN-R was trained to optimize the Brier skill score (BSS). As a result, we achieved BSS = 0.41 for >=C-class flare predictions and 0.30 for >=M-class flare predictions by improving the reliability diagram while keeping the relative operating characteristic curve almost the same. Note that DeFN is optimized for deterministic prediction, which is determined with a normalized threshold of 50%. On the other hand, DeFN-R is optimized for a probability forecast based on the observation event rate, whose probability threshold can be selected according to users' purposes.


[56] 2007.02566

Evolutionary status and fundamental parameters of the Cepheid V1033 Cyg

On the basis of consistent stellar evolution and nonlinear stellar pulsation calculations the Cepheid V1033 Cyg is shown to be the post--main sequence star at the first crossing of the instability strip during gravitational contraction of the helium core. The observed light variability of V1033 Cyg is due to radial oscillations in the fundamental mode. The best agreement (within one percent) between recent observations and the theoretical estimate of the period change rate was obtained for the evolutionary sequence with stellar mass $M=6.3M_\odot$ and helium and heavier element fractional abundances $Y=0.28$ and $Z=0.022$, respectively. The age of the star, the luminosity, the radius, the effective temperature and the surface gravity are $t_\mathrm{ev}=5.84\times 10^7$ yr, $L=2009L_\odot$, $R=45.6R_\odot$, $T_\mathrm{eff}=5726 \mathrm{K}$, $\log g=1.92$.


[57] 2007.02583

Dark Matter as Perfect Fluid in Low Surface Brightness Galaxies

When dark matter is a perfect fluid, using the equation of state can get the density profile in the static and spherically symmetric space-time. If the equation of state is independent of the scaling transformation, its lower order approximation can naturally lead to a special case, i.e. $p=\zeta\rho+2\epsilon V_{rot}^{2}\rho$, where $p$ and $\rho$ are the the pressure and density, $V_{rot}$ is the rotation velocity of galaxy, $\zeta$ and $ \epsilon$ are positive constants. Then we use this equation of state to derive the mass density profiles of dark matter halos. It can obtain a profile which is similar to the pseudo-isothermal halo model when $\epsilon$ is around $0.15$. It can perfectly fit the observed rotation curves of low surface brightness (LSB) galaxies. When $\zeta=0$, there exits a power law density in the very outer region which surround a black hole, and its power index is $-\frac{1+4\epsilon}{4\epsilon}$. The term $\zeta\rho$ can lead to a constant-density core.


[58] 2007.02585

Seismic evidence for near solid-body rotation in two Kepler subgiants and implications for angular momentum transport

Asteroseismic measurements of the internal rotation of subgiants and red giants all show the need for invoking a more efficient transport of angular momentum than theoretically predicted. Constraints on the core rotation rate are available starting from the base of the red giant branch (RGB) and we are still lacking information on the internal rotation of less evolved subgiants. We identified two young Kepler subgiants, KIC8524425 and KIC5955122, whose mixed modes are clearly split by rotation. Using the full Kepler data set, we extracted the mode frequencies and rotational splittings for the two stars using a Bayesian approach. We then performed a detailed seismic modeling of both targets and used the rotational kernels to invert their internal rotation profiles. We found that both stars are rotating nearly as solid bodies, with core-envelope contrasts of $\Omega_{\rm g}/\Omega_{\rm p}=0.68\pm0.47$ for KIC8524425 and $0.72\pm0.37$ for KIC5955122. This result shows that the internal transport of angular momentum has to occur faster than the timescale at which differential rotation is forced in these stars (between 300 Myr and 600 Myr). By modeling the additional transport of angular momentum as a diffusive process with a constant viscosity $\nu_{\rm add}$, we found that values of $\nu_{\rm add}>5\times10^4$~cm$^2$.s$^{-1}$ are required to account for the internal rotation of KIC8524425, and $\nu_{\rm add}>1.5\times10^5$~cm$^2$.s$^{-1}$ for KIC5955122. These values are lower than or comparable to the efficiency of the core-envelope coupling during the main sequence, as given by the surface rotation of stars in open clusters. On the other hand, they are higher than the viscosity needed to reproduce the rotation of subgiants near the base of the RGB. Our results yield further evidence that the efficiency of the internal redistribution of angular momentum decreases during the subgiant phase.


[59] 2007.02610

Improving impact monitoring through Line Of Variations densification

We propose a densification algorithm to improve the Line Of Variations (LOV) method for impact monitoring, which can fail when the information is too little, as it may happen in difficult cases. The LOV method uses a 1-dimensional sampling to explore the uncertainty region of an asteroid. The close approaches of the sample orbits are grouped by time and LOV index, to form the so-called returns, and each return is analysed to search for local minima of the distance from the Earth along the LOV. The strong non-linearity of the problem causes the occurrence of returns with so few points that a successful analysis can be prevented. Our densification algorithm tries to convert returns with length at most 3 in returns with 5 points, properly adding new points to the original return. Due to the complex evolution of the LOV, this operation is not necessarily achieved all at once: in this case the information about the LOV geometry derived from the first attempt is exploited for a further attempt. Finally, we present some examples showing that the application of our method can have remarkable consequences on impact monitoring results, in particular about the completeness of the virtual impactors search.


[60] 2007.02612

Quasars at intermediate redshift are not special; but they are often satellites

Understanding the links between the activity of supermassive black holes (SMBH) at the centres of galaxies and their host dark matter haloes is a key question in modern astrophysics. The final data release of the SDSS-IV eBOSS provides the largest contemporary spectroscopic sample of galaxies and QSOs. Using this sample and covering the redshift interval $z=0.7-1.1$, we have measured the clustering properties of the eBOSS QSOs, Emission Line Galaxies (ELGs) and Luminous Red Galaxies (LRGs). We have also measured the fraction of QSOs as a function of the overdensity defined by the galaxy population. Using these measurements, we investigate how QSOs populate and sample the galaxy population, and how the host dark-matter haloes of QSOs sample the underlying halo distribution. We find that the probability of a galaxy hosting a QSO is independent of the host dark matter halo mass of the galaxy. We also find that about 60\% of eBOSS QSOs are hosted by LRGs and about 20-40\% of QSOs are hosted by satellite galaxies. We find a slight preference for QSOs to populate satellite galaxies over central galaxies. This is connected to the host halo mass distribution of different types of galaxies. Based on our analysis, QSOs should be hosted by a very broad distribution of haloes, and their occurrence should be modulated only by the efficiency of galaxy formation processes.


[61] 2007.02615

Boosting MonteCarlo sampling with a non-Gaussian fit

We propose a new method, called MonteCarlo Posterior Fit, to boost the MonteCarlo sampling of likelihood (posterior) functions. The idea is to approximate the posterior function by an analytical multidimensional non-Gaussian fit. The many free parameters of this fit can be obtained by a smaller sampling than is needed to derive the full numerical posterior. In the examples that we consider, based on supernovae and cosmic microwave background data, we find that one needs an order of magnitude smaller sampling than in the standard algorithms to achieve comparable precision. This method can be applied to a variety of situations and is expected to significantly improve the performance of the MonteCarlo routines in all the cases in which sampling is very time-consuming. Finally, it can also be applied to Fisher matrix forecasts, and can help solve various limitations of the standard approach.


[62] 2007.02616

A hard look at local, optically-selected, obscured Seyfert galaxies

We study the X-ray spectra of a sample of 19 obscured, optically-selected Seyfert galaxies (Sy 1.8, 1.9 and 2) in the local universe ($d \leq 175$~Mpc), drawn from the CfA Seyfert sample. Our analysis is driven by the high sensitivity of NuSTAR in the hard X-rays, coupled with soft X-ray spectra using XMM-Newton, Chandra, Suzaku, and Swift/XRT. We also analyze the optical spectra of these sources in order to obtain accurate mass estimates and Eddington fractions. We employ four different models to analyze the X-ray spectra of these sources, which all result in consistent results. We find that 79-90 % of the sources are heavily obscured with line-of-sight column density $N_{\rm H} > 10^{23}~\rm cm^{-2}$. We also find a Compton-thick ($N_{\rm H} > 10^{24}~\rm cm^{-2}$) fraction of $37-53$ %. These results are consistent with previous estimates based on multi-wavelength analyses. We find that the fraction of reprocessed to intrinsic emission is positively correlated with $N_{\rm H}$ and negatively correlated with the intrinsic, unabsorbed, X-ray luminosity (in agreement with the Iwasawa-Taniguchi effect). Our results support the hypothesis that radiation pressure regulates the distribution of the circumnuclear material.


[63] 2007.02625

On the Dependency between the Peak Velocity of High-speed Solar Wind Streams near Earth and the Area of Their Solar Source Coronal Holes

The relationship between the peak velocities of high-speed solar wind streams near Earth and the areas of their solar source regions, i.e., coronal holes, has been known since the 1970s, but it is still physically not well understood. We perform 3D magnetohydrodynamic (MHD) simulations using the European Heliospheric Forecasting Information Asset (EUHFORIA) code to show that this empirical relationship forms during the propagation phase of high-speed streams from the Sun to Earth. For this purpose, we neglect the acceleration phase of high-speed streams, and project the areas of coronal holes to a sphere at 0.1 au. We then vary only the areas and latitudes of the coronal holes. The velocity, temperature, and density in the cross section of the corresponding highspeed streams at 0.1 au are set to constant, homogeneous values. Finally, we propagate the associated high-speed streams through the inner heliosphere using the EUHFORIA code. The simulated high-speed stream peak velocities at Earth reveal a linear dependence on the area of their source coronal holes. The slopes of the relationship decrease with increasing latitudes of the coronal holes, and the peak velocities saturate at a value of about 730 km/s, similar to the observations. These findings imply that the empirical relationship between the coronal hole areas and high-speed stream peak velocities does not describe the acceleration phase of high-speed streams, but is a result of the high-speed stream propagation from the Sun to Earth.


[64] 2007.02626

The turbulence driving parameter of molecular clouds in disc galaxies

Supersonic turbulence plays a pivotal role during the formation of molecular clouds and stars in galaxies. However, little is known about how the fraction of compressive and solenoidal modes in the velocity field evolves over time and how it depends on properties of the molecular cloud or the galactic environment. In this work, we carry out magnetohydrodynamical simulations of disc galaxies and study the time evolution of the turbulence driving parameter for an ensemble of clouds. We find that the time-averaged turbulence driving parameter is insensitive to the position of the cloud within the galaxy. The ensemble-averaged driving parameter is found to be rather compressive with $b\sim0.5-0.7$, indicating almost time-independent global star formation properties. However, each individual cloud shows a highly fluctuating driving parameter, which would strongly affect the cloud's star formation rate. We find that the mode of turbulence driving can rapidly change within only a few Myr, both from solenoidal to compressive and vice versa. We attribute these changes to cloud collisions and to tidal interactions with clouds or overdensities in the environment. Last, we find no significant differences in the average driving parameter between hydrodynamic and initially strongly magnetised galaxies. However, the magnetic field tends to reduce the overall fluctuation of the driving parameter. The average driving as well as its uncertainty are seen to be in agreement with recent constraints on the turbulence driving mode for solar neighbourhood clouds.


[65] 2007.02631

Euclid preparation: VIII. The Complete Calibration of the Colour-Redshift Relation survey: VLT/KMOS observations and data release

The Complete Calibration of the Colour-Redshift Relation survey (C3R2) is a spectroscopic effort involving ESO and Keck facilities designed to empirically calibrate the galaxy colour-redshift relation - P(z|C) to the Euclid depth (i_AB=24.5) and is intimately linked to upcoming Stage IV dark energy missions based on weak lensing cosmology. The aim is to build a spectroscopic calibration sample that is as representative as possible of the galaxies of the Euclid weak lensing sample. In order to minimise the number of spectroscopic observations to fill the gaps in current knowledge of the P(z|C), self-organising map (SOM) representations of the galaxy colour space have been constructed. Here we present the first results of an ESO@ VLT Large Programme approved in the context of C3R2, which makes use of the two VLT optical and near-infrared multi-object spectrographs, FORS2 and KMOS. This paper focuses on high-quality spectroscopic redshifts of high-z galaxies observed with the KMOS spectrograph in the H- and K-bands. A total of 424 highly-reliable z are measured in the 1.3<=z<=2.5 range, with total success rates of 60.7% in the H-band and 32.8% in the K-band. The newly determined z fill 55% of high and 35% of lower priority empty SOM grid cells. We measured Halpha fluxes in a 1."2 radius aperture from the spectra of the spectroscopically confirmed galaxies and converted them into star formation rates. In addition, we performed an SED fitting analysis on the same sample in order to derive stellar masses, E(B-V), total magnitudes, and SFRs. We combine the results obtained from the spectra with those derived via SED fitting, and we show that the spectroscopic failures come from either weakly star-forming galaxies (at z<1.7, i.e. in the H-band) or low S/N spectra (in the K-band) of z>2 galaxies.


[66] 2007.02651

The Exoplanet Perspective on Future Ice Giant Exploration

Exoplanets number in their thousands, and the number is ever increasing with the advent of new surveys and improved instrumentation. One of the most surprising things we have learnt from these discoveries is not that small-rocky planets in their stars habitable zones are likely common, but that the most typical size of exoplanet is that not seen in our solar system - radii between that of Neptune and the Earth dubbed mini-Neptunes and super-Earths. In fact, a transiting exoplanet is four times as likely to be in this size regime than that of any giant planet in our solar system. Investigations into the atmospheres of giant hydrogen/helium dominated exoplanets has pushed down to Neptune and mini-Neptune sized worlds revealing molecular absorption from water, scattering and opacity from clouds, and measurements of atmospheric abundances. However, unlike measurements of Jupiter, or even Saturn sized worlds, the smaller giants lack a ground truth on what to expect or interpret from their measurements. How did these sized worlds form and evolve and was it different from their larger counterparts? What is their internal composition and how does that impact their atmosphere? What informs the energy budget of these distant worlds? In this we discuss what characteristics we can measure for exoplanets, and why a mission to the ice giants in our solar system is the logical next step for understanding exoplanets.


[67] 2007.02668

Investigation of the Middle Corona with SWAP and a Data-Driven Non-Potential Coronal Magnetic Field Model

The large field-of-view of the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) instrument on board the PRoject for Onboard Autonomy 2 (PROBA2) spacecraft provides a unique opportunity to study extended coronal structures observed in EUV in conjunction with global coronal magnetic field simulations. A global non-potential magnetic field model is used to simulate the evolution of the global corona from 1 September 2014 to 31 March 2015, driven by newly emerging bipolar active regions determined from Helioseismic and Magnetic Imager (HMI) magnetograms. We compare the large-scale structure of the simulated magnetic field with structures seen off-limb in SWAP EUV observations. In particular, we investigate how successful the model is in reproducing regions of closed and open structures; the scale of structures; and compare the evolution of a coronal fan observed over several rotations. The model is found to accurately reproduce observed large-scale off-limb structures. When discrepancies do arise they mainly occur off the east solar limb due to active regions emerging on the far side of the Sun, which cannot be incorporated into the model until they are observed on the Earth-facing side. When such ``late'' active region emergences are incorporated into the model, we find that the simulated corona self-corrects within a few days, so that simulated structures off the west limb more closely match what is observed. Where the model is less successful, we consider how this may be addressed, through model developments or additional observational products.


[68] 2007.02678

Magnetic field amplification in accretion discs around the first stars: implications for the primordial IMF

Magnetic fields play an important role in the dynamics of present-day molecular clouds. Recent work has shown that magnetic fields are equally important for primordial clouds, which form the first stars in the Universe. While the primordial magnetic field strength on cosmic scales is largely unconstrained, theoretical models strongly suggest that a weak seed field existed in the early Universe. We study how the amplification of such a weak field can influence the evolution of accretion discs around the first stars, and thus affect the primordial initial mass function (IMF). We perform a suite of 3D magneto-hydrodynamic (MHD) simulations with different initial field strengths and numerical resolutions. We find that, in simulations with sufficient spatial resolution to resolve the Jeans scale during the collapse, even initially weak magnetic fields grow exponentially to become dynamically important due to both the so-called \textit{small-scale turbulent dynamo} and the \textit{large-scale mean-field dynamo}. Capturing the small-scale dynamo action depends primarily on how well we resolve the Jeans length, while capturing the large-scale dynamo depends on the Jeans resolution as well as the maximum absolute resolution. Provided enough resolution, we find that fragmentation does not depend strongly on the initial field strength, because even weak fields grow to become strong. However, fragmentation in runs with magnetic fields differs significantly from those without magnetic fields. We conclude that the development of dynamically strong magnetic fields during the formation of the first stars is likely inevitable, and that these fields had a significant impact on the primordial IMF.


[69] 2007.02685

The Scattering of Dirac Spinors in Rotating Spheroids

There are many stars that are rotating spheroids in the Universe, and studying them is of very important significance. Since the times of Newton, many astronomers and physicists have researched gravitational properties of stars by considering the moment equations derived from Eulerian hydrodynamic equations. In this paper we study the scattering of spinors of the Dirac equation, and in particular investigate the scattering issue in the limit case of rotating Maclaurin spheroids. Firstly we give the metric of a rotating ellipsoid star, then write the Dirac equation under this metric, and finally derive the scattering solution to the Dirac equation and establish a relation between differential scattering cross-section, $\sigma$, and stellar matter density, $\mu$. It is found that the sensitivity of $\sigma$ to the change in $\mu$ is proportional to the density $\mu$. Because of weak gravitational field and constant mass density, our results are reasonable. The results can be applied to white dwarfs, main sequence stars, red giants, supergiant stars and so on, as long as their gravitational fields are so weak that they can be treated in the Newtonan approximations, and the fluid is assumed to be incompressible. Notice that we take the star's matter density to be its average density and the star is not taken to be compact. Obviously our results cannot be used to study neutron stars and black holes. In particular, our results are suitable for white dwarfs, which have average densities of about $10^{5}-10^{6}$\,g~cm$^{-3}$, corresponding to a range of mass of about $0.21-0.61 M_{\bigodot}$ and a range of radius of about $6000-10000$\,km.


[70] 2007.02702

Detection of the magnetar XTE J1810-197 at 150 and 260 GHz with the NIKA2 Kinetic Inductance Detector camera

The investigation of pulsars between millimetre and optical wavelengths is challenging due to the faintness of the pulsar signals and the relative low sensitivity of the available facilities compared to 100-m class telescopes operating in the centimetre band. The Kinetic Inductance Detector (KID) technology offers large instantaneous bandwidths and a high sensitivity that can help to substantially increase the ability of existing observatories at short wavelengths to detect pulsars and transient emission. To investigate the feasibility of detecting pulsars with KIDs, we observed the anomalous X-ray pulsar XTE J1810-197 with the New IRAM KIDs Array-2 (NIKA2) camera installed at the IRAM 30-m Telescope in Spain. We detected the pulsations from the pulsar with NIKA2 at its two operating frequency bands, 150 and 260 GHz ($\lambda$=2.0 and 1.15 mm, respectively). This is the first time that a pulsar is detected with a receiver based on KID technology in the millimetre band. In addition, this is the first report of short millimetre emission from XTE J1810-197 after its reactivation in December 2018, and it is the first time that the source is detected at 260 GHz, which gives us new insights into the radio emission process of the star.


[71] 2007.02716

A temperature inversion with atomic iron in the ultra-hot dayside atmosphere of WASP-189b

Temperature inversion layers are predicted to be present in ultra-hot giant planet atmospheres. Although such inversion layers have been observed in several ultra-hot Jupiters recently, the chemical species responsible for creating the inversion remain unidentified. Here, we present observation of the thermal emission spectrum of an ultra-hot Jupiter, WASP-189b, at high spectral resolution using the HARPS-N spectrograph. Using the cross-correlation technique, we detect a strong Fe I signal. The detected Fe I spectral lines are found in emission, which is a direct evidence of a temperature inversion in the planetary atmosphere. We further performed a retrieval on the observed spectrum using a forward model with an MCMC approach. When assuming a solar metallicity, the best-fit result returns a temperature of $4320_{-100}^{+120}$ K at the top of the inversion, which is significantly hotter than the planetary equilibrium temperature (2641 K). The temperature at the bottom of the inversion is determined as $2200_{-800}^{+1000}$ K. Such a strong temperature inversion is probably created by the absorption of atomic species like Fe I.


[72] 2007.02741

The GTC exoplanet transit spectroscopy survey XI. Possible detection of Rayleigh scattering in the atmosphere of the Saturn-mass planet WASP-69b

One of the major atmospheric features in exoplanet atmospheres, detectable both from ground- and space-based facilities, is Rayleigh scattering. In hydrogen-dominated planetary atmospheres Rayleigh scattering causes the measured planetary radius to increase towards blue wavelengths in the optical range. We obtained a spectrophotometic time series of one transit of the Saturn-mass planet WASP-69b using the OSIRIS instrument at the Gran Telescopio Canarias. From the data we construct 19 spectroscopic transit light curves representing 20 nm wide wavelength bins spanning from 515 nm - 905 nm. We derive the transit depth for each curve individually by fitting an analytical model together with a Gaussian Processes to account for systematic noise in the light curves. We find that the transit depth increases towards bluer wavelengths, indicative of a larger effective planet radius. Our results are consistent with space-based measurements obtained in the near infrared using the Hubble Space telescope, which show a compatible slope of the transmission spectrum. We discuss the origin of the detected slope and argue between two possible scenarios: a Rayleigh scattering detection originating in the planet's atmosphere or a stellar activity induced signal from the host star.


[73] 2007.02744

The mass, spin and rotational energy of the remnant black holes from compact binary mergers

Recently, many gravitational wave events from compact binary mergers have been detected by LIGO. Determining the final mass and spin of the remnant black holes (RBHs) is a fundamental issue and is also important in astrophysics. In this paper, unified models for predicting the final mass and spin of the RBHs from compact binary mergers is proposed. The models achieve a good accuracy within the parameter range of interest. In addition, the rotational energy of the RBHs is also studied which is relevant to the electromagnetic counterparts of the mergers. It is found the distribution of the rotational energy of the RBHs from different types of mergers of compact binary has its own characteristics, which might help identify the electromagnetic counterparts associated with the mergers.


[74] 2007.02748

Turbulent, pinned superfluids in neutron stars and pulsar glitch recoveries

Pulsar glitches offer an insight into the dynamics of superfluids in the high density interior of a neutron star. To model these phenomena, however, one needs to have an understanding of the dynamics of a turbulent array of superfluid vortices moving through a pinning lattice. In this paper we develop a theoretical approach to describe vortex mediated mutual friction in a pinned, turbulent and rotating superfluid. Our model is then applied to the study of the post glitch rotational evolution in the Vela pulsar and in PSR J0537-6910. We show that in both cases a turbulent model fits the evolution of the spin frequency derivative better than a laminar one. We also predict that the second derivative of the frequency after a glitch should be correlated with the waiting time since the previous glitch, which we find to be consistent with observational data for these pulsars. The main conclusion of this paper is that in the post-glitch rotational evolution of these two pulsars we are most likely observing the response to the glitch of a pinned turbulent region of the star (possibly the crust) and not the laminar response of a regular straight vortex array.


[75] 2007.02778

A Search for Supernova Light Echoes in NGC 6946 with SITELLE

We present the analysis of four hours of spectroscopic observations of NGC 6946 with the SITELLE Imaging Fourier Transform Spectrometer on the Canada-France-Hawaii Telescope, acquired to search for supernova light echoes from its ten modern supernovae. We develop a novel spectroscopic search method: identifying negatively sloped continua in the narrow-band SN3 filter as candidate highly-broadened P-Cygni profiles in the H$\alpha$ line, which would be characteristic of the spectra of supernovae ejecta. We test our methodology by looking for light echoes from any of the ten supernovae observed in NGC 6946 in the past 100 years. We find no evidence of light echoes above the survey surface brightness limit of 1$\times$10$^{-15}$erg/s/cm$^2$/arcsec$^2$.


[76] 2007.02797

Massive Galaxies Impede Massive Outflows

A set of 66 3D hydrodynamical simulations explores how galactic stellar mass affects three-phase, starburst-driven outflows. Simulated velocities are compared to two basic analytic models: with (Johnson \& Axford 1971) and without (Chevalier \& Clegg 1985) a gravitational potential. For stellar mass $<10^{10}$ solar masses, simulated velocities match those of both analytical models and are unaffected by the potential; above they reduce significantly as expected from the analytic model with gravity. Gravity also affects total outflow mass and each of the three phases differently. Outflow mass in the hot, warm, and cold phases each scale with stellar mass as $\log M_*=$ -0.25, -0.97, and -1.70, respectively. Thus, the commonly used Chevalier \& Clegg analytic model should be modified to include gravity when applied to higher mass galaxies. In particular, using M82 as the canonical galaxy to interpret hydrodynamical simulations of starburst-driven outflows from higher mass galaxies will underestimate the retarding effect of gravity. Using the analytic model of Johnson \& Axford with realistic thermalization efficiency and mass loading I find that only galaxy masses that are less than $\sim10^{11.5}$ solar masses can outflow.


[77] 2007.02810

On the Chemical Abundance of HR 8799 and the Planet c

Comparing chemical abundances of a planet and the host star reveals the origin and formation path. Stellar abundance is measured with high-resolution spectroscopy. Planet abundance, on the other hand, is usually inferred from low-resolution data. For directly imaged exoplanets, the data are available from a slew of high-contrast imaging/spectroscopy instruments. Here, we study the chemical abundance of HR 8799 and its planet c. We measure stellar abundance using LBT/PEPSI (R=120,000) and archival HARPS data: stellar [C/H], [O/H], and C/O are 0.11$\pm$0.12, 0.12$\pm$0.14, and 0.54$^{+0.12}_{-0.09}$, all consistent with solar values. We conduct atmospheric retrieval using newly obtained Subaru/CHARIS data together with archival Gemini/GPI and Keck/OSIRIS data. We model the planet spectrum with petitRADTRANS and conduct retrieval using PyMultiNest. Retrieved planetary abundance can vary by $\sim$0.5 dex, from sub-stellar to stellar C and O abundances. The variation depends on whether strong priors are chosen to ensure a reasonable planet mass. Moreover, comparison with previous works also reveals inconsistency in abundance measurements. We discuss potential issues that can cause the inconsistency, e.g., systematics in individual data sets and different assumptions in the physics and chemistry in retrieval. We conclude that no robust retrieval can be obtained unless the issues are fully resolved.


[78] 2007.02826

Evidence for ammonia-bearing species on the Uranian satellite Ariel supports recent geologic activity

We investigated whether ammonia-rich constituents are present on the surface of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra collected over a wide range of sub-observer longitudes and latitudes. We measured the band areas and depths of a 2.2-{\micron} feature in these spectra, which has been attributed to ammonia-bearing species on other icy bodies. Ten spectra display prominent 2.2-{\micron} features with band areas and depths > 2{\sigma}. We determined the longitudinal distribution of the 2.2-{\micron} band, finding no statistically meaningful differences between Ariel's leading and trailing hemispheres, indicating that this band is distributed across Ariel's surface. We compared the band centers and shapes of the five Ariel spectra displaying the strongest 2.2-{\micron} bands to laboratory spectra of various ammonia-bearing and ammonium-bearing species, finding that the spectral signatures of the Ariel spectra are best matched by ammonia-hydrates and flash frozen ammonia-water solutions. Our analysis also revealed that four Ariel spectra display 2.24-{\micron} bands (> 2{\sigma} band areas and depths), with band centers and shapes that are best matched by ammonia ice. Because ammonia should be efficiently removed over short timescales by ultraviolet photons, cosmic rays, and charged particles trapped in Uranus' magnetosphere, the possible presence of this constituent supports geologic activity in the recent past, such as emplacement of ammonia-rich cryolavas and exposure of ammonia-rich deposits by tectonism, impact events, and mass wasting.


[79] 2007.02836

Revisiting the relation between nonthermal line widths and transverse MHD wave amplitudes

Observations and 3D MHD simulations of the transverse MHD waves in the solar corona have established that true wave energies hide in the nonthermal line widths of the optically thin emission lines. This displays the need for a relation between the nonthermal line widths and transverse wave amplitudes for estimating the true wave energies. In the past decade, several studies have assumed that the root mean square (rms) wave amplitudes are larger than nonthermal line widths by a factor of $\sqrt{2}$. However, a few studies have ignored this factor while estimating rms wave amplitudes. Thus there appears to exist a discrepancy in this relation. In this study, we investigate the dependence of nonthermal line widths on wave amplitudes by constructing a simple mathematical model followed by 3D MHD simulations. We derive this relation for the linearly polarised, circularly polarised oscillations, and oscillations excited by multiple velocity drivers. We note a fairly good match between mathematical models and numerical simulations. We conclude that the rms wave amplitudes are never greater than the nonthermal line widths which raises questions about earlier studies claiming transverse waves carry enough energy to heat the solar corona.


[80] 2007.02838

Comprehensive analysis of magnetospheric gaps around Kerr black holes using 1D GRPIC simulations

Spark gaps are likely the source of plasma in active black hole (BH) magnetospheres. In this paper, we present results of 1D general-relativistic particle-in-cell simulations of a starved BH magnetosphere with a realistic treatment of inverse Compton scattering and pair production, for a broad range of conditions, run times longer than in previous studies, and different setups. We find that following the initial discharge, the system undergoes gradual evolution over prolonged time until either, restoring the vacuum state or reaching a state of quasi-periodic oscillations, depending on the spectral shape and luminosity of the ambient radiation field. The oscillations occur near the null charge surface in cases where the global magnetospheric current is negative, and near the boundary of the simulation box when it is positive. Their amplitude and the resultant luminosity of TeV photons emitted from the gap depend sensitively on the conditions; for the cases studied here the ratio of TeV luminosity to the Blandford-Znajek power ranges from $10^{-5}$ to $10^{-2}$, suggesting that strong flares may be generated by moderate changes in disk emission. We also examined the dependence of the solution on the initial number of particles per cell (PPC) and found convergence for PPC of about 50 for the cases examined. At lower PPC values the pair multiplicity is found to be artificially high, affecting the solution considerably.


[81] 2007.02865

Searching for dark energy in the matter-dominated era

Most efforts to detect signatures of dynamical dark energy are focused on late times, $z \lesssim 2$, where the dark energy component begins to dominate the cosmic energy density. Many theoretical models involving dynamical dark energy exhibit a 'freezing' equation of state however, where $w \to -1$ at late times, with a transition to a 'tracking' behaviour at earlier times (with $w \gg -1$ at sufficiently high redshift). In this paper, we study whether large-scale structure surveys in the post-reionisation matter-dominated regime, $2 \lesssim z \lesssim 6$, are sensitive to this behaviour, on the basis that the dark energy component should remain detectable (despite being strongly subdominant) in this redshift range given sufficiently precise observations. Using phenomenological models inspired by parameter space studies of Horndeski (generalised scalar-tensor) theories, we show how existing CMB and large-scale structure measurements constrain the dark energy equation of state in the matter-dominated era, and examine how forthcoming galaxy surveys and 21cm intensity mapping instruments can improve constraints in this regime. We also find that the combination of existing CMB and LSS constraints with DESI will already come close to offering the best possible constraints on $H_0$ using BAO/galaxy power spectrum measurements, and that either a spectroscopic follow-up of the LSST galaxy sample (e.g. along the lines of MegaMapper or SpecTel) or a Stage 2/PUMA-like intensity mapping survey, both at $z \gtrsim 2$, would offer better constraints on the class of dark energy models considered here than a comparable cosmic variance-limited galaxy survey at $z \lesssim 1.5$.


[82] 2007.02881

Thermal inertias of pebble-pile comet 67P/Churyumov-Gerasimenko

The Rosetta mission to comet 67P/Churyumov-Gerasimenko has provided new data to better understand what comets are made of. The weak tensile strength of the cometary surface materials suggests that the comet is a hierarchical dust aggregate formed through gravitational collapse of a bound clump of small dust aggregates so-called ``pebbles'' in the gaseous solar nebula. Since pebbles are the building blocks of comets, which are the survivors of planetesimals in the solar nebula, estimating the size of pebbles using a combination of thermal observations and numerical calculations is of great importance to understand the planet formation in the outer solar system. In this study, we calculated the thermal inertias and thermal skin depths of the hierarchical aggregates of pebbles, for both diurnal and orbital variations of the temperature. We found that the thermal inertias of the comet 67P/Churyumov-Gerasimenko are consistent with the hierarchical aggregate of cm- to dm-sized pebbles. Our findings indicate that the icy planetesimals may have formed via accretion of cm- to dm-sized pebbles in the solar nebula.


[83] 2007.02883

Dark Sirens to Resolve the Hubble-Lemaître Tension

The planned sensitivity upgrades to the LIGO and Virgo facilities could uniquely identify host galaxies of dark sirens-compact binary coalescences without any electromagnetic counterparts-within a redshift of z = 0.1. This is aided by the higher order spherical harmonic modes present in the gravitational-wave signal, which also improve distance estimation. In conjunction, sensitivity upgrades and higher modes will facilitate an accurate, independent measurement of the host galaxy's redshift in addition to the luminosity distance from the gravitational wave observation to infer the Hubble-Lema\^itre constant H0 to better than a few percent in five years. A possible Voyager upgrade or third generation facilities would further solidify the role of dark sirens for precision cosmology in the future.


[84] 2007.02886

Dispersion measure: Confusion, Constants & Clarity

The dispersion measure (DM) is one of the key attributes of radio pulsars and Fast Radio Bursts (FRBs). There is a mistaken view that the DM is an accurate measure of the column density of electrons between the observer and the source. To start with, the DM, unlike a true column density, is not a Lorentz invariant. Next, the DM also includes contribution from ions and is sensitive to the temperature of the plasma in the intervening clouds. Separately, the primary observable is the dispersion slope, $\mathcal{D}\equiv \Delta{(t)}/\Delta{(\nu^{-2}})$, where $t(\nu)$ is the arrival time at frequency, $\nu$. A scaling factor composed of physical and astronomical constants is needed to convert $\mathcal{D}$ to DM. In the early days of pulsar astronomy the relevant constants were defined to parts per million (ppm). As a result, a convention arose in which this conversion factor was fixed. Over time, several such conventions came about -- recipe for confusion. Meanwhile, over the past several years, the SI system has been restructured and the parsec is now exactly defined. As a result, the present accuracy of the conversion factor is below a part per billion -- many orders of magnitude better than the best measurement errors of $\mathcal{D}$. We are now in an awkward situation wherein the primary "observable", the DM, has incorrect scaling factor(s). To address these two concerns I propose that astronomers report the primary measurement, $\mathcal{D}$ (with a suggested normalization of $10^{15}\,$Hz), and not the DM. Interested users can convert $\mathcal{D}$ to DM without the need to know secret handshakes of the pulsar timing communities.


[85] 2007.02888

The Gaia-ESO Survey: Galactic evolution of lithium at high metallicity

Reconstructing the Galactic evolution of lithium (Li) is the main tool used to constrain the source(s) of Li enrichment in the Galaxy. Recent results have suggested a decline in Li at supersolar metallicities, which may indicate reduced production. We exploit the unique characteristics of the Gaia-ESO Survey open star cluster sample to further investigate this issue and to better constrain the evolution of Li at high metallicity. We trace the the upper envelope of Li abundance versus metallicity evolution using 18 clusters and considering members that should not have suffered any Li depletion. At variance with previous claims, we do not find any evidence of a Li decrease at high metallicity. The most metal-rich clusters in the sample ([Fe/H] about 0.3) actually show the highest Li abundances, with A(Li) > 3.4. Our results clearly show that previous findings, which were based on field stars, were affected by selection effects. The metal-rich population in the solar neighbourhood is composed of relatively old and cool stars that have already undergone some Li depletion; hence, their measured Li does not represent the initial interstellar medium abundance, but a lower limit to it.


[86] 2007.02889

Wind-powered afterglows of gamma-ray bursts: flares, plateaus and steep decays

Afterglows of gamma-ray bursts often show flares, plateaus, and sudden intensity drops: these temporal features are difficult to explain as coming from the forward shock. We calculate radiative properties of early GRB afterglows with the dominant contribution from the reverse shock (RS) propagating in an ultra-relativistic (pulsar-like) wind produced by the long-lasting central engine. RS emission occurs in the fast cooling regime - this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that: (i) mild wind power, of the order of $\sim 10^{46}$ erg s$^{-1}$, can reproduce the afterglows' plateau phase; (ii) termination of the wind can produce sudden steep decays; (iii) mild variations in the wind luminosity can produce short-duration afterglow flares.


[87] 2007.02899

The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue

Sky surveys produce enormous quantities of data on extensive regions of the sky. The easiest way to access this information is through catalogues of standardised data products. {\em XMM-Newton} has been surveying the sky in the X-ray, ultra-violet, and optical bands for 20 years. The {\em XMM-Newton} Survey Science Centre has been producing standardised data products and catalogues to facilitate access to the serendipitous X-ray sky. Using improved calibration and enhanced software, we re-reduced all of the 14041 {\em XMM-Newton} X-ray observations, of which 11204 observations contained data with at least one detection and with these we created a new, high quality version of the {\em XMM-Newton} serendipitous source catalogue, 4XMM-DR9. 4XMM-DR9 contains 810795 detections down to a detection significance of 3 $\sigma$, of which 550124 are unique sources, which cover 1152 degrees$^{2}$ (2.85\%) of the sky. Filtering 4XMM-DR9 to retain only the cleanest sources with at least a 5 $\sigma$ detection significance leaves 433612 detections. Of these detections, 99.6\% have no pileup. Furthermore, 336 columns of information on each detection are provided, along with images. The quality of the source detection is shown to have improved significantly with respect to previous versions of the catalogues. Spectra and lightcurves are also made available for more than 288000 of the brightest sources (36\% of all detections).


[88] 2007.02920

Local dark energy in the Sculptor Filament of galaxies

Two dozens of different mass galaxies observed at distances less than 10 Mpc from the Local Group are organized in the elongated structure known as the Sculptor Filament. We use recent Hubble Space Telescope data on local galaxies to study the dynamical structure and evolutionary trends of the filament. An N-body computer model, which reproduces its observed kinematics, is constructed under the assumption that the filament is embedded in the universal dark energy background. In the model, the motions of the filament members are controlled by their mutual gravity attraction force and the anti-gravity repulsion force produced by the local dark energy. It is found that the dark energy repulsion dominates the force field of the outer parts of the filament. Because of this, the filament expands and its expansion proceeds with acceleration. The dark energy domination increases with cosmic time and introduces to the filament the linear velocity--distance relation with the universal time-rate ("the Hubble constant") that depends asymptotically on the dark energy density only.


[89] 2007.02921

Small glitches and other rotational irregularities of the Vela pulsar

Glitches are sudden accelerations of the rotation rate $\nu$ of neutron stars, believed to be driven by the neutron superfluid inside the star's crust and core. They present a wide phenomenology and their amplitudes $\Delta\nu$ span over six orders of magnitude. The 21 known glitches of the Vela pulsar are amongst the largest observed (typically $\Delta\nu/\nu\sim10^{-6}$) and have very similar characteristics. We wish to explore the population of small-amplitude rotational changes in the Vela pulsar and determine the rate of occurrence and sizes of its smallest glitches. We use high cadence observations of the Vela pulsar taken between 1981 and 2005 by the Mount Pleasant Radio Observatory. An automated, systematic search was carried out that investigates whether a significant change of spin frequency $\nu$ and/or the spin-down rate $\dot{\nu}$ takes place at any given time. Our study reveals numerous events of all possible signatures (i.e. combinations of $\Delta\nu$ and $\Delta\dot{\nu}$ signs), usually small, with $|\Delta\nu|/\nu<10^{-9}$, which contribute to Vela's timing noise. We also find two glitches that have not been reported before, with respective sizes $\Delta\nu/\nu$ of $(5.55\pm0.03)\times10^{-9}$ and $(38\pm4)\times10^{-9}$. The latter glitch is followed by an exponential-like recovery with characteristic timescale of $\sim30$ d. The Vela pulsar presents an under-abundance of small glitches comparatively to many other glitching pulsars, which appears genuine and not a result of observational biases. Besides typical glitches, the smooth spin down of the pulsar is also affected by an almost continuous activity that can be partially characterised by step-like changes in $\nu$, $\dot{\nu}$ or both.


[90] 2007.02927

A complete model of Phenomenologically Emergent Dark Energy

The Phenomenologically Emergent Dark Energy model, a dark energy model with the same number of free parameters as the flat $\Lambda$CDM, has been proposed as a working example of a minimal model which can avoid the current cosmological tensions. A straightforward question is whether or not the inclusion of massive neutrinos and extra relativistic species may spoil such an appealing phenomenological alternative. We present the bounds on $M_{\nu}$ and $N_{\rm eff}$ and comment on the long standing $H_0$ and $\sigma_8$ tensions within this cosmological framework with a wealth of cosmological observations. Interestingly, we find, at $95\%$ confidence level, and with the most complete set of cosmological observations, $M_{\nu}\sim 0.21^{+0.15}_{-0.14}$ eV and $N_{\rm eff}= 3.03\pm 0.32$ i.e. an indication for a non-zero neutrino mass with a significance above $2\sigma$. The well known Hubble constant tension is considerably easened, with a significance always below the $2\sigma$ level.


[91] 2007.02930

pinta: The uGMRT Data Processing Pipeline for the Indian Pulsar Timing Array

We introduce pinta, a pipeline for reducing the uGMRT raw pulsar timing data developed for the Indian Pulsar Timing Array experiment. We provide a detailed description of the workflow and usage of pinta, as well as its computational performance and RFI mitigation characteristics. Furthermore, the results of a calibration experiment carried out to determine the relative time offsets between different back-end modes and the correct interpretation of the observatory frequency settings at the uGMRT, which are crucial for performing precision pulsar timing, are also discussed.


[92] 2007.02932

The XMM-Newton serendipitous survey. X: The second source catalogue from overlapping XMM-Newton observations and its long-term variable content

The XMM-Newton Survey Science Centre Consortium (SSC) develops software in close collaboration with the Science Operations Centre to perform a pipeline analysis of all XMM-Newton observations. In celebration of the 20th launch anniversary, the SSC has compiled the 4th generation of serendipitous source catalogues, 4XMM. The catalogue described here, 4XMM-DR9s, explores sky areas that were observed more than once by XMM-Newton. It was constructed from simultaneous source detection on the overlapping observations, which were bundled in groups ("stacks"). Stacking leads to a higher sensitivity, resulting in newly discovered sources and better constrained source parameters, and unveils long-term brightness variations. As a novel feature, positional rectification was applied beforehand. Observations with all filters and suitable camera settings were included. Exposures with a high background were discarded, which was determined through a statistical analysis of all exposures in each instrument configuration. The X-ray background maps used in source detection were modelled via adaptive smoothing with newly determined parameters. Source fluxes were derived for all contributing observations, irrespective of whether the source would be detectable in an individual observation. From 1,329 stacks with 6,604 contributing observations over repeatedly covered 300 square degrees in the sky, 4XMM-DR9s lists 288,191 sources. 218,283 of them were observed several times. Most stacks are composed of two observations, the largest one comprises 352. The number of observations of a source ranges from 1 to 40. Auxiliary products like X-ray images, long-term light curves, and optical finding charts are published as well. 4XMM-DR9s is considered a prime resource to explore long-term variability of X-ray sources discovered by XMM-Newton. Regular incremental releases including new public observations are planned.


[93] 2006.14016

Anisotropic Einstein Yang-Mills Higgs Dark Energy

In the context of the dark energy scenario, the Einstein Yang-Mills Higgs model in the SO(3) representation was studied for the first time by M. Rinaldi (see JCAP 1510, 023 (2015)) in a homogeneous and isotropic spacetime. We revisit this model, finding in particular that the interaction between the Higgs field and the gauge fields generates contributions to the momentum density, anisotropic stress and pressures, thus making the model inconsistent with the assumed background. We instead consider a homogeneous but anisotropic Bianchi-I spacetime background in this paper and analyze the corresponding dynamical behaviour of the system. We find that the only attractor point corresponds to an isotropic accelerated expansion dominated by the Higgs potential. However, the model predicts non-negligible anisotropic shear contributions nowadays, i.e. the current universe can have hair although it will loose it in the future. We investigate the evolution of the equation of state for dark energy and highlight some possible consequences of its behaviour related to the process of large-scale structure formation. As a supplement, we propose the "Higgs triad" as a possibility to make the Einstein Yang-Mills Higgs model be consistent with a homogeneous and isotropic spacetime.


[94] 2007.01873

Constraints on Axion-Lepton coupling from Big Bang Nucleosynthesis

In this article, we study the implications of the coupling between Axion-Like-Particles (ALPs) and Leptons to cosmology, in particular, the Big Bang Nucleosynthesis (BBN). We show that the BBN, through the constraint on the effective number of relativistic neutrino species, provides the most stringent bound on the ALP-electron interaction strength for the mass of axion between 20 keV and 1 MeV. For other values of the mass, the BBN bound complements the stellar-evolution and laboratory bounds.


[95] 2007.01968

Generalized Rastall's gravity and its effects on compact objects

We present a generalization of Rastall's gravity in which the conservation law of the energy-moment tensor is altered, and as a result, the trace of the energy-moment tensor is taken into account together with the Ricci scalar in the expression for the covariant derivative. Afterwards, we obtain the field equation in this theory and solve it by considering a spherically symmetric space-time. We show that the external solution has two possible classes of solutions with spherical symmetry in the vacuum in generalized Rastall's gravity. The first class of solutions is completely equivalent to the Schwarzschild solution, while the second class of solutions has the same structure as the Schwarzschild--de Sitter solution in general relativity. The generalization, in contrast to constant value $k=8\pi G$ in general relativity, has a gravitational parameter $k$ that depends on the energy density $\rho$. As an application, we perform a careful analysis of the effects of the theory on neutron stars using realistic equations of state (EoS) as inputs. Our results show that important differences on the profile of neutron stars are obtained within two representatives EoS.


[96] 2007.02309

Non-Minimally Coupled Einstein Gauss Bonnet Inflation Phenomenology in View of GW170817

We study the inflationary phenomenology of a non-minimally coupled Einstein Gauss-Bonnet gravity theory, in the presence of a scalar potential, under the condition that the gravitational wave speed of the primordial gravitational waves is equal to unity, that is $c_T^2=1$, in natural units. The equations of motion, which are derived directly from the gravitational action, form a system of differential equations with respect to Hubble's parameter and the inflaton field which are very complicated and cannot be solved analytically, even in the minimal coupling case. In this paper, we present a variety of different approximations which could be used, along with the constraint $c_T^2=1$, in order to produce an inflationary phenomenology compatible with recent observations. All the different approaches are able to lead to viable results if the model coupling functions obey simple relations, however, different approaches contain different approximations which must be obeyed during the first horizon crossing, in order for the model to be rendered correct. Models which may lead to a non-viable phenomenology are presented as well in order to understand better the inner framework of this theory. Furthermore, since the velocity of the gravitational waves is set equal to $c_T^2=1$, as stated by the striking event of GW170817 recently, the non-minimal coupling function, the Gauss-Bonnet scalar coupling and the scalar potential are related to each other. Here, we shall assume no particular form of the scalar potential and we choose freely the scalar functions coupled to the Ricci scalar and the Gauss-Bonnet invariant. Certain models are also studied in order to assess the phenomenological validity of the theory, but we need to note that all approximations must hold true in order for a particular model to be valid.


[97] 2007.02369

Interplay between Swampland and Bayesian Machine Learning in constraining cosmological models

Constraints on a dark energy dominated Universe are obtained from an interplay between Bayesian Machine Learning and string Swampland criteria. The approach here differs from previous studies, since in the generative process Swampland criteria are used and, only later, the results of the fit are validated, by using observational data-sets. A generative process based Bayesian Learning approach is applied to two models and the results are validated by means of available $H(z)$ data. For the first model, a parametrization of the Hubble constant is considered and, for the second, a parametrization of the deceleration parameter. This study is motivated by a recent work, where constraints on string Swampland criteria have been obtained from a Gaussian Process and $H(z)$ data. However, the results obtained here are fully independent of the observational data and allow to estimate how the high-redshift behavior of the Universe will affect the low-redshift one. Moreover, both parameterizations in the generative process, for the Hubble and for the deceleration parameters, are independent of the dark energy model. The outcome, both data- and dark energy model-independent, may highlight, in the future, the borders of the Swampland for the low-redshift Universe and help to develop new string-theory motivated dark-energy models. The string Swampland criteria considered might be in tension with recent observations indicating that phantom dark energy cannot be in the Swampland. Finally, a spontaneous sign switch in the dark energy equation of state parameter is observed when the field traverses are in the $z\in[0,5]$ redshift range, a remarkable phenomenon requiring further analysis.


[98] 2007.02395

Gravitational Particle Production in Loop Quantum Cosmology

We investigate the gravitational particle production in the bounce phase of Loop Quantum Cosmology (LQC). We perform both analytical and numerical analysis of the particle production process in a LQC scenario with Bunch-Davies vacuum initial condition in the contracting phase. We obtain that if we extend the validity of the dressed metric approach beyond the limit of small backreaction in which it is well justified, this process would lead to a radiation dominated phase in the pre-inflationary phase of LQC. Our results indicate that the test field approximation, which is required in the truncation scheme used in the dressed metric approach, might not be a valid assumption in a LQC scenario with such initial conditions.


[99] 2007.02828

Long range enhanced mutual information from inflation

The quantum origin of cosmological primordial perturbations is a cornerstone framework in the interplay between gravity and quantum physics. In this paper we study the mutual information between two spatial regions in a radiation-dominated universe filled by a curvature perturbation field in a squeezed state. We find an enhancement with respect to the usual mutual information of the Minkowski vacuum due to momentum modes affected by particle production during inflation. This result supports our previous claim of the existence of quantum entanglement between Primordial Black Holes (PBH) at formation during the radiation era.


[100] 2007.02898

Dark Matter $Z^\prime$ and XENON1T Excess from $U(1)_X$ Extended Standard Model

A gauged $U(1)_X$ symmetry appended to the Standard Model (SM) is particularly well-motivated since it can account for the light neutrino masses by the seesaw mechanism, explain the origin of baryon asymmetry of the universe via leptogenesis, and help implement successful cosmological inflation with the $U(1)_X$ breaking Higgs field as the inflaton. In this framework, we propose a light dark matter (DM) scenario in which the $U(1)_X$ gauge boson $Z^\prime$ behaves as a DM particle in the universe. We discuss how this scenario with $Z^\prime$ mass of a few keV and a $U(1)_X$ gauge coupling $g_X \simeq 10^{-16}$ can nicely fit the excess in the electronic recoil energy spectrum recently reported by the XENON1T collaboration. In order to reproduce the observed DM relic density in the presence of such a tiny gauge coupling, we propose an extension of the model to a two-component DM scenario. The $Z^\prime$ DM density can be comparable to the observed DM density by the freeze-in mechanism through the coupling of $Z^\prime$ boson to a partner Higgs-portal scalar DM with a large $U(1)_X$ charge.