New articles on astro-ph


[1] 2009.07844

The surprising accuracy of isothermal Jeans modelling of self-interacting dark matter density profiles

Recent claims of observational evidence for self-interacting dark matter (SIDM) have relied on a semi-analytic method for predicting the density profiles of galaxies and galaxy clusters containing SIDM. We present a thorough description of this method, known as isothermal Jeans modelling, and then test it with a large ensemble of haloes taken from cosmological simulations. Our simulations were run with cold and collisionless dark matter (CDM) as well as two different SIDM models, all with dark matter only variants as well as versions including baryons and relevant galaxy formation physics. Using a mix of different box sizes and resolutions, we study haloes with masses ranging from 3e10 to 3e15 Msun. Overall, we find that the isothermal Jeans model provides as accurate a description of simulated SIDM density profiles as the Navarro-Frenk-White profile does of CDM halos. We can use the model predictions, compared with the simulated density profiles, to determine the input DM-DM scattering cross-sections used to run the simulations. This works especially well for large cross-sections, while with CDM our results tend to favour non-zero (albeit fairly small) cross-sections, driven by a bias against small cross-sections inherent to our adopted method of sampling the model parameter space. The model works across the whole halo mass range we study, although including baryons leads to DM profiles of intermediate-mass (10^12 - 10^13 Msun) haloes that do not depend strongly on the SIDM cross-section. The tightest constraints will therefore come from lower and higher mass haloes: dwarf galaxies and galaxy clusters.


[2] 2009.07845

Cluster Difference Imaging Photometric Survey. II. TOI 837: A Young Validated Planet in IC 2602

We report the discovery of TOI 837b and its validation as a transiting planet. We characterize the system using data from the NASA TESS mission, the ESA Gaia mission, ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI 837 is a $T=9.9$ mag G0/F9 dwarf in the southern open cluster IC 2602. The star and planet are therefore $35^{+11}_{-5}$ million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color-magnitude diagram, we find that the planet has an orbital period of $8.3\,{\rm d}$ and is slightly smaller than Jupiter ($R_{\rm p} = 0.77^{+0.09}_{-0.07} \,R_{\rm Jup}$). From radial velocity monitoring, we limit $M_{\rm p}\sin i$ to less than 1.20 $M_{\rm Jup}$ (3-$\sigma$). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multi-color photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI 837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time.


[3] 2009.07846

The Archetypal Ultra-Diffuse Galaxy, Dragonfly 44, is not a Dark Milky Way

Due to the peculiar properties of ultra-diffuse galaxies (UDGs), understanding their origin presents a major challenge. Previous X-ray studies demonstrated that the bulk of UDGs lack substantial X-ray emission, implying that they reside in low-mass dark matter halos. This result, in concert with other observational and theoretical studies, pointed out that most UDGs belong to the class of dwarf galaxies. However, a subset of UDGs is believed to host a large population of globular clusters (GCs), which is indicative of massive dark matter halos. This, in turn, hints that some UDGs may be failed $\rm L_{\star}$ galaxies. In this work, I present Chandra and XMM-Newton observations of two archetypal UDGs, Dragonfly 44 and DF X1, and I constrain their dark matter halo mass based on the X-ray emission originating from hot gaseous emission and from the population of low-mass X-ray binaries residing in GCs. Both Dragonfly 44 and DF X1 remain undetected in X-rays. The upper limits on the X-ray emission exclude the possibility that these galaxies reside in massive ($M_{\rm vir} \gtrsim 5\times10^{11} \ \rm{M_{\odot}}$) dark matter halos, suggesting that they are not failed $\rm L_{\star}$ galaxies. These results demonstrate that even these iconic UDGs resemble to dwarf galaxies with $M_{\rm vir} \lesssim 10^{11} \ \rm{M_{\odot}}$, implying that UDGs represent a single galaxy population.


[4] 2009.07854

Strongly lensed candidates from the HSC transient survey

We present a lensed quasar search based on the time variability of lens systems in the HSC transient survey. Starting from 101,353 variable objects with $\textit{i}$-band difference images in the HSC transient survey, we use a time-variability-based lens search method measuring the spatial extendedness in difference images to select potential lensed quasar candidates. We adopt conservative constraints in this variability selection and obtain 83,657 variable objects as possible lens candidates. We then run CHITAH, a lens search algorithm based on the image configuration, on those 83,657 variable objects, and 2,130 variable objects are identified as lensed objects. We visually inspect the 2,130 variable objects, and seven of them are our final candidates of lensed quasars. Additionally, we find one lensed galaxy candidate as a serendipitous discovery. Among the eight final lensed candidates, one is the only known quadruply lensed quasar in the survey field, HSCJ095921+020638. None of the other seven lensed candidates has been previously classified as a lens nor a lensed candidate. Three of the five final candidates with available Hubble Space Telescope (HST) images, including HSCJ095921+020638, show clues of lensed feature in the HST images. A tightening of variability selection criteria might result in the loss of possible lensed quasar candidates, especially the lensed quasars with faint brightness or narrow separation, without efficiently eliminating the non-lensed objects; CHITAH is therefore important as an advanced examination to improve the lens search efficiency through the object configuration. The recovery of HSCJ095921+020638 proves the feasibility of the time-variability-based lens search method, and this lens search method can be used in other cadenced imaging surveys, such as the upcoming Rubin Observatory Legacy Survey of Space and Time.


[5] 2009.07856

SN2019yvq Does Not Conform to SN Ia Explosion Models

We present new photometric and spectroscopic observations of SN 2019yvq, a Type Ia supernova (SN Ia) exhibiting several peculiar properties including an excess of UV/optical flux within days of explosion, a high SiII velocity, and a low peak luminosity. Photometry near the time of first light places new constraints on the rapid rise of the UV/optical flux excess and shows that it peaks $\sim 2$ days earlier than previously thought. A near-infrared spectrum at $+173$ days after maximum light places strict limits on the presence of H or He emission, effectively excluding the presence of a nearby non-degenerate star at the time of explosion. New optical spectra, acquired at +128 and +150 days after maximum light, confirm the presence of CaII$\lambda 7300~$\r{A} and persistent CaII NIR triplet emission as SN 2019yvq transitions into the nebular phase. The lack of [OI]$\lambda 6300~$\r{A} emission disfavors the violent merger of two C/O white dwarfs (WDs) but the merger of a C/O WD with a He WD cannot be excluded. We compare our findings with several models in the literature postulated to explain the early flux excess including double-detonation explosions, $^{56}$Ni mixing into the outer ejecta during ignition, and interaction with H- and He-deficient circumstellar material. Each model may be able to explain both the early flux excess and the nebular [CaII] emission, but none of the models can reconcile the high photospheric velocities with the low peak luminosity without introducing new discrepancies.


[6] 2009.07857

The role of collision speed, cloud density, and turbulence in the formation of young massive clusters via cloud-cloud collisions

Young massive clusters (YMCs) are recently formed astronomical objects with unusually high star formation rates. We propose the collision of giant molecular clouds (GMCs) as a likely formation mechanism of YMCs, consistent with the YMC conveyor-belt formation mode concluded by other authors. We conducted smoothed particle hydrodynamical simulations of cloud-cloud collisions and explored the effect of the clouds' collision speed, initial cloud density, and the level of cloud turbulence on the global star formation rate and the properties of the clusters formed from the collision. We show that greater collision speed, greater initial cloud density and lower turbulence increase the overall star formation rate and produce clusters with greater cluster mass. In general, collisions with relative velocity $\gtrsim 25$ km/s, initial cloud density $\gtrsim 250$ cm$^{-3}$, and turbulence of $\approx 2.5$ km/s can produce massive clusters with properties resembling the observed Milky Way YMCs.


[7] 2009.07858

Near-Gaussian distributions for modelling discrete stellar velocity data with heteroskedastic uncertainties

The velocity distributions of stellar tracers in general exhibit weak non-Gaussianity encoding information on the orbital composition of a galaxy and the underlying potential. The standard solution for measuring non-Gaussianity involves constructing a series expansion (e.g. the Gauss-Hermite series) which can produce regions of negative probability density. This is a significant issue for the modelling of discrete data with heteroskedastic uncertainties. Here, we introduce a method to construct positive-definite probability distributions by the convolution of a given kernel with a Gaussian distribution. Further convolutions by observational uncertainties are trivial. The statistics (moments and cumulants) of the resulting distributions are governed by the kernel distribution. Two kernels (uniform and Laplace) offer simple drop-in replacements for a Gauss-Hermite series for negative and positive excess kurtosis distributions with the option of skewness. We demonstrate the power of our method by an application to real and mock line-of-sight velocity datasets on dwarf spheroidal galaxies, where kurtosis is indicative of orbital anisotropy and hence a route to breaking the mass-anisotropy degeneracy for the identification of cusped versus cored dark matter profiles. Data on the Fornax dwarf spheroidal galaxy indicate positive excess kurtosis and hence favour a cored dark matter profile. Although designed for discrete data, the analytic Fourier transforms of the new models also make them appropriate for spectral fitting, which could improve the fits of high quality data by avoiding unphysical negative wings in the line-of-sight velocity distribution.


[8] 2009.07859

SDSS-IV MaNGA: The link between bars and the early cessation of star formation in spiral galaxies

Bars are common in low-redshift disk galaxies, and hence quantifying their influence on their host is of importance to the field of galaxy evolution. We determine the stellar populations and star formation histories of 245 barred galaxies from the MaNGA galaxy survey, and compare them to a mass- and morphology-matched comparison sample of unbarred galaxies. At fixed stellar mass and morphology, barred galaxies are optically redder than their unbarred counterparts. From stellar population analysis using the full spectral fitting code Starlight, we attribute this difference to both older and more metal-rich stellar populations. Dust attenuation however, is lower in the barred sample. The star formation histories of barred galaxies peak earlier than their non-barred counterparts, and the galaxies build up their mass at earlier times. We can detect no significant differences in the local environment of barred and un-barred galaxies in this sample, but find that the HI gas mass fraction is significantly lower in high-mass ($\rm{M}_{\star} > 10^{10}~\rm{M}_{\odot}$) barred galaxies than their non-barred counterparts. We speculate on the mechanisms that have allowed barred galaxies to be older, more metal-rich and more gas-poor today, including the efficient redistribution of galactic fountain byproducts, and a runaway bar formation scenario in gas-poor disks. While it is not possible to fully determine the effect of the bar on galaxy quenching, we conclude that the presence of a bar and the early cessation of star formation within a galaxy are intimately linked.


[9] 2009.07860

Shaping the structure of a GMC with radiation and winds

We study the effect of stellar feedback (photodissociation/ionization, radiation pressure and winds) on the evolution of a Giant Molecular Cloud (GMC), by means of a 3D radiative transfer, hydro-simulation implementing a complex chemical network featuring ${\rm H}_2$ formation and destruction. We track the formation of individual stars with mass $M>1\,{\rm M}_\odot$ with a stochastic recipe. Each star emits radiation according to its spectrum, sampled with 10 photon bins from near-infrared to extreme ultra-violet bands; winds are implemented by energy injection in the neighbouring cells. We run a simulation of a GMC with mass $M=10^5\,{\rm M}_\odot$, following the evolution of different gas phases. Thanks to the simultaneous inclusion of different stellar feedback mechanisms, we identify two stages in the cloud evolution: (1) radiation and winds carve ionized, low-density bubbles around massive stars, while FUV radiation dissociates most ${\rm H}_2$ in the cloud, apart from dense, self-shielded clumps; (2) rapid star formation (SFR$\simeq 0.1\,{\rm M}_\odot\,{\rm yr}^{-1}$) consumes molecular gas in the dense clumps, so that UV radiation escapes and ionizes the remaining HI gas in the GMC. ${\rm H}_2$ is exhausted in $1.6$ Myr, yielding a final star formation efficiency of 36 per cent. The average intensity of FUV and ionizing fields increases almost steadily with time; by the end of the simulation ($t=2.5$ Myr) we find $\langle G_0 \rangle \simeq 10^3$ (in Habing units), and a ionization parameter $\langle U_{\rm ion} \rangle \simeq 10^2$, respectively. The ionization field has also a more patchy distribution than the FUV one within the GMC. Throughout the evolution, the escape fraction of ionizing photons from the cloud is $f_{\rm ion, esc} < 0.03$.


[10] 2009.07861

The H$α$ star formation main sequence in cluster and field galaxies at $z\sim1.6$

We calculate H$\alpha$-based star formation rates and determine the star formation rate-stellar mass relation for members of three SpARCS clusters at $z \sim 1.6$ and serendipitously identified field galaxies at similar redshifts to the clusters. We find similar star formation rates in cluster and field galaxies throughout our range of stellar masses. The results are comparable to those seen in other clusters at similar redshifts, and consistent with our previous photometric evidence for little quenching activity in clusters. One possible explanation for our results is that galaxies in our $z \sim 1.6$ clusters have been accreted too recently to show signs of environmental quenching. It is also possible that the clusters are not yet dynamically mature enough to produce important environmental quenching effects shown to be important at low redshift, such as ram pressure stripping or harassment.


[11] 2009.07869

Estimating the Ultraviolet Emission of M dwarfs with Exoplanets from Ca II and H$α$

M dwarf stars are excellent candidates around which to search for exoplanets, including temperate, Earth-sized planets. To evaluate the photochemistry of the planetary atmosphere, it is essential to characterize the UV spectral energy distribution of the planet's host star. This wavelength regime is important because molecules in the planetary atmosphere such as oxygen and ozone have highly wavelength dependent absorption cross sections that peak in the UV (900-3200 $\r{A}$). We seek to provide a broadly applicable method of estimating the UV emission of an M dwarf, without direct UV data, by identifying a relationship between non-contemporaneous optical and UV observations. Our work uses the largest sample of M dwarf star far- and near-UV observations yet assembled. We evaluate three commonly-observed optical chromospheric activity indices -- H$\alpha$ equivalent widths and log$_{10}$ L$_{H\alpha}$/L$_{bol}$, and the Mount Wilson Ca II H&K S and R$'_{HK}$ indices -- using optical spectra from the HARPS, UVES, and HIRES archives and new HIRES spectra. Archival and new Hubble Space Telescope COS and STIS spectra are used to measure line fluxes for the brightest chromospheric and transition region emission lines between 1200-2800 $\r{A}$. Our results show a correlation between UV emission line luminosity normalized to the stellar bolometric luminosity and Ca II R$'_{HK}$ with standard deviations of 0.31-0.61 dex (factors of $\sim$2-4) about the best-fit lines. We also find correlations between normalized UV line luminosity and H$\alpha$ log$_{10}$ L$_{H\alpha}$/L$_{bol}$ and the S index. These relationships allow one to estimate the average UV emission from M0 to M9 dwarfs when UV data are not available.


[12] 2009.07870

Using Multichannel Singular Spectrum Analysis to Study Galaxy Dynamics

N-body simulations provide most of our insight into the structure and evolution of galaxies, but our analyses of these are often heuristic and from simple statistics. We propose a method that discovers the dynamics in space and time together by finding the most correlated temporal signals in multiple time series of basis function expansion coefficients and any other data fields of interest. The method extracts the dominant trends in the spatial variation of the gravitational field along with any additional data fields through time. The mathematics of this method is known as multichannel singular spectrum analysis (M-SSA). In essence, M-SSA is a principal component analysis of the covariance of time series replicates, each lagged successively by some interval. The dominant principal component represents the trend that contains the largest fraction of the correlated signal. The next principal component is orthogonal to the first and contains the next largest fraction, and so on. Using a suite of previously analysed simulations, we find that M-SSA describes bar formation and evolution, including mode coupling and pattern-speed decay. We also analyse a new simulation tailored to study vertical oscillations of the bar using kinematic data. Additionally, and to our surprise, M-SSA uncovered some new dynamics in previously analysed simulations, underscoring the power of this new approach.


[13] 2009.07886

The NICER View of the 2020 Burst Storm and Persistent Emission of SGR 1935+2154

We report NICER observations of the most intense bursting period yet from the magnetar SGR 1935+2154, focusing on 2020 April 28 from 00:40:58 to 16:21:19 UTC, an interval that ends <2 hours after the fast radio burst (FRB) associated with the source. During the first 1120 seconds we detect over 217 bursts, corresponding to a burst rate of >0.2 bursts/s. Three hours later the rate is at 0.008 bursts/s, remaining at a comparatively low level thereafter. The $T_{90}$ duration distribution of the bursts peaks at 840 ms; the distribution of waiting times to the next burst is fit with a log-normal with an average of 2.1 s. The 1-10 keV spectra of the bursts are well fit by a single blackbody, with an average temperature and area of kT=1.7 keV and $R^2=53$ km$^2$. The differential burst fluence distribution over ~3 orders of magnitude is well modeled with a power-law form $dN/dF\propto F^{-1.5\pm0.1}$. Our timing analysis of the source persistent emission, after the initial burst storm, retrieves the magnetar spin period and derives a double-peaked pulse profile. There is no discernible correlation of the 217 burst peak times with pulse phase. However, we find that the arrival time of the FRB aligns in phase with the brightest peak of the pulse profile. Finally, we present the persistent emission spectral evolution up to 2020 July 26; its flux and blackbody temperature decrease rapidly in the early stages of the outburst, reaching quiescence 40 days later, while the size of the emitting area remains unchanged.


[14] 2009.07905

Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources

A significant fraction of all $\gamma$-ray sources detected by the Large Area Telescope aboard the \fer\ satellite is still lacking a low-energy counterpart. In addition, there is still a large population of $\gamma$-ray sources with associated low-energy counterparts that lack firm classifications. In the last 10 years we have undertaken an optical spectroscopic campaign to address the problem of unassociated/unidentified $\gamma$-ray sources (UGSs), mainly devoted to observing blazars and blazar candidates because they are the largest population of $\gamma$-ray sources associated to date. Here we describe the overall impact of our optical spectroscopic campaign on sources associated in \fer-LAT catalogs, coupled with objects found in the literature. In the literature search, we kept track of efforts by different teams that presented optical spectra of counterparts or potential counterparts of \fer-LAT catalog sources. Our summary includes an analysis of an additional 30 newly-collected optical spectra of counterparts or potential counterparts of \fer-LAT sources of previously unknown nature.New spectra were acquired at the Blanco 4-m and OAN-SPM 2.1-m telescopes, and those available in the Sloan Digital Sky Survey (data release 15) archive. All new sources with optical spectra analyzed here are classified as blazars. Thanks to our campaign, we altogether discovered and classified 394 targets with an additional 123 objects collected from a literature search. We began our optical spectroscopic campaign between the release of the second and third \fer-LAT source catalogs (2FGL and 3FGL, respectively), and classified about 25\% of the sources with uncertain nature and discovered a blazar-like potential counterpart for $\sim$10\% of UGSs listed therein. In the 4FGL catalog, about 350 \fer-LAT sources are classified to date thanks to our campaign. [incomplete abstract]


[15] 2009.07924

A deep Chandra survey for faint X-ray sources in the Galactic globular cluster M30, and searches for optical and radio counterparts

We present a deep ($\sim 330~\mathrm{ks}$) {\it Chandra} survey of the Galactic globular cluster M30 (NGC 7099). Combining the new Cycle 18 with the previous Cycle 3 observations we report a total of 10 new X-ray point sources within the $1.03$ arcmin half-light radius, compiling an extended X-ray catalogue of a total of 23 sources. We incorporate imaging observations by the {\it Hubble Space Telescope} and the {\it Karl G. Jansky Very Large Array} from the MAVERIC survey to search for optical and radio counterparts to the new and old sources. Two X-ray sources are found to have a radio counterpart, including the known millisecond pulsar PSR J2140$-$2310A, the radio position of which also matches a previously reported faint optical counterpart which is slightly redder than the main sequence. We found optical counterparts to $18$ of the $23$ X-ray sources, identifying $2$ new cataclysmic variables (CVs), $5$ new CV candidates, $2$ new candidates of RS CVn type of active binary (AB), and $2$ new candidates of BY Dra type of AB. The remaining unclassified X-ray sources are likely background active galactic nuclei (AGN), as their number is consistent with the expected number of AGN at our X-ray sensitivity. Finally, our analysis of radial profiles of different source classes suggests that bright CVs are more centrally distributed than faint CVs in M30, consistent with other core-collapsed globular clusters.


[16] 2009.07927

A Reanalysis of Public Galactic Bulge Gravitational Microlensing Events from OGLE-III and IV

Modern surveys of gravitational microlensing events have progressed to detecting thousands per year. Surveys are capable of probing Galactic structure, stellar evolution, lens populations, black hole physics, and the nature of dark matter. One of the key avenues for doing this is studying the microlensing Einstein radius crossing time distribution ($t_E$). However, systematics in individual light curves as well as over-simplistic modeling can lead to biased results. To address this, we developed a model to simultaneously handle the microlensing parallax due to Earth's motion, systematic instrumental effects, and unlensed stellar variability with a Gaussian Process model. We used light curves for nearly 10,000 OGLE-III and IV Milky Way bulge microlensing events and fit each with our model. We also developed a forward model approach to infer the timescale distribution by forward modeling from the data rather than using point estimates from individual events. We find that modeling the variability in the baseline removes a source of significant bias in individual events, and previous analyses over-estimated the number of long timescale ($t_E>100$ days) events due to their over simplistic models ignoring parallax effects and stellar variability. We use our fits to identify hundreds of events that are likely black holes.


[17] 2009.07939

Design of the New Wideband Vivaldi Feed for the HERA Radio-Telescope Phase II

This paper presents the design of a new dual-polarised Vivaldi feed for the Hydrogen Epoch of Reionization Array (HERA) radio-telescope. This wideband feed has been developed to replace the phase I dipole feed, and is used to illuminate a 14-m diameter dish. It aims to improve the science capabilities of HERA, by allowing it to characterise the 21-cm hydrogen signal from the Cosmic Dawn as well as from the Epoch of Reionization. This is achieved by increasing the bandwidth from 100 -- 200 MHz to 50 -- 250 MHz, optimising the time response of the antenna - receiver system, and improving its sensitivity. This new Vivaldi feed is directly fed by a differential front-end module placed inside the circular cavity and connected to the back-end via cables which pass in the middle of the tapered slot. We show that this particular configuration has minimal effects on the radiation pattern and on the system response.


[18] 2009.07945

Search for high-redshift blazars with Fermi/LAT

High-$z$ blazars (z $\geq 2.5$) are the most powerful class of persistent $\gamma$-ray sources in the Universe. These objects possess the highest jet powers and luminosities and have black hole masses often in excess of $10^9$ solar masses. In addition, high-$z$ blazars are important cosmological probes and serve as test objects for blazar evolution models. Due to their large distance, their high-energy emission typically peaks below the GeV range, which makes them difficult to study with Fermi/LAT. Therefore, only the very brightest objects are detectable and, to date, only a small number of high-z blazars have been detected with Fermi/LAT. In this work, we studied the monthly binned long-term $\gamma$-ray emission of a sample of 176 radio and optically detected blazars that have not been reported as known $\gamma$-ray sources in the 3FGL catalog. In order to account for false-positive detections, we calculated monthly Fermi/LAT light curves for a large sample of blank sky positions and derived the number of random fluctuations that we expect at various test statistic (TS) levels. For a given blazar, a detection of TS > 9 in at least one month is expected $\sim 15\%$ of the time. Although this rate is too high to secure detection of an individual source, half of our sample shows such single-month $\gamma$-ray activity, indicating a population of high-energy blazars at distances of up to z=5.2. Multiple TS > 9 monthly detections are unlikely to happen by chance, and we have detected several individual new sources in this way, including the most distant $\gamma$-ray blazar, BZQ J1430+4204 (z = 4.72). Finally, two new $\gamma$-ray blazars at redshifts of z = 3.63 and z = 3.11 are unambiguously detected via very significant (TS > 25) flares in individual monthly time bins.


[19] 2009.08019

Detection of a Disk Surrounding the Variably Accreting Young Star HBC722

We present new ALMA 233 GHz continuum observations of the FU Orionis Object HBC722. With these data we detect HBC722 at millimeter wavelengths for the first time, use this detection to calculate a circumstellar disk mass of 0.024 solar masses, and discuss implications for the burst triggering mechanism.


[20] 2009.08029

Transformative Planetary Science with the US ELT Program

The proposed US Extremely Large Telescope (ELT) Program would secure national open access to at least 25% of the observing time on the Thirty Meter Telescope in the north and the Giant Magellan Telescope in the south. ELTs would advance solar system science via exceptional angular resolution, sensitivity, and advanced instrumentation. ELT contributions would include the study of interstellar objects, giant planet systems and ocean worlds, the formation of the solar system traced through small objects in the asteroid and Kuiper belts, and the active support of planetary missions. We recommend that (1) the US ELT Program be listed as critical infrastructure for solar system science, that (2) some support from NASA be provided to ensure mission support capabilities, and that (3) the US ELT Program expand solar-system community participation in development, planning, and operations.


[21] 2009.08051

The role of dust destruction and dust growth in the evolution of the interstellar medium

We use Milky Way-like chemodynamical simulations with a new treatment for dust destruction and growth to investigate how these two processes affect the properties of the interstellar medium in galaxies. We focus on the role of two specific parameters: f_des (a new parameter that determines the fraction of dust destroyed in a single gas particle surrounding supernova) and C_s (the probability that a metal atom or ion sticks to the dust grain after colliding, i.e., the sticking coefficient) in regulating the amount and distribution of dust, cold gas and metals in galaxies. We find that simulated galaxies with low f_des and/or high C_s values produce not only more dust, but they also have a shallower correlation between dust surface density and total gas surface density, and a steeper correlation between dust-to-gas ratio and metallicity. Only for values of f_des between 0.01 and 0.02, and of C_s between 0.5 and 1 our simulations produce an average slope of the dust-to-gas ratio versus metallicity relation consistent with observations. f_des values correspond to a range of a total fraction of dust destroyed by a single supernova between 0.42 and 0.44. Lastly, we compare predictions of several simulations (with different star formation recipes, gas fractions, central metallicities, and metallicity gradients) to the spatially resolved M101 galaxy, and conclude that metallicity is the primary driver of the spatial distribution of dust, while dust-to-gas ratio controls the cold gas distribution, as it regulates the atomic-to-molecular hydrogen conversion rate.


[22] 2009.08057

Persistent mysteries of jet engines, formation, propagation, and particle acceleration: have they been addressed experimentally?

The physics of astrophysical jets can be divided into three regimes: (i) engine and launch (ii) propagation and collimation, (iii) dissipation and particle acceleration. Since astrophysical jets comprise a huge range of scales and phenomena, practicality dictates that most studies of jets intentionally or inadvertently focus on one of these regimes, and even therein, one body of work may be simply boundary condition for another. We first discuss long standing persistent mysteries that pertain the physics of each of these regimes, independent of the method used to study them. This discussion makes contact with frontiers of plasma astrophysics more generally. While observations theory, and simulations, and have long been the main tools of the trade, what about laboratory experiments? Jet related experiments have offered controlled studies of specific principles, physical processes, and benchmarks for numerical and theoretical calculations. We discuss what has been done to date on these fronts. Although experiments have indeed helped us to understand certain processes, proof of principle concepts, and benchmarked codes, they have yet to solved an astrophysical jet mystery on their own. A challenge is that experimental tools used for jet-related experiments so far, are typically not machines originally designed for that purpose, or designed with specific astrophysical mysteries in mind. This presents an opportunity for a different way of thinking about the development of future platforms: start with the astrophysical mystery and build an experiment to address it.


[23] 2009.08068

MAMMOTH: Confirmation of Two Massive Galaxy Overdensities at $z=2.24$ with H$α$ Emitters

Massive galaxy overdensities at the peak epoch of cosmic star formation provide ideal testbeds for the formation theories of galaxies and large-scale structure. We report the confirmation of two massive galaxy overdensities at $z=2.24$, BOSS1244 and BOSS1542, selected from the MAMMOTH project using Ly$\alpha$ absorption from the intergalactic medium over the scales of 15$-$30 $h^{-1}$ Mpc imprinted on the quasar spectra. We use H$\alpha$ emitters (HAEs) as the density tracer and identify them using deep narrowband $H_2S1$ and broadband $K_{\rm s}$ imaging data obtained with CFHT/WIRCam. In total, 244 and 223 line emitters are detected in these two fields, and $196\pm 2$ and $175\pm 2$ are expected to be HAEs with an H$\alpha$ flux of $> 2.5\times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ (corresponding to an SFR of $>$5 M$_\odot$ yr$^{-1}$). The detection rate of HAE candidates suggests an overdensity factor of $\delta_{\rm gal}=5.6\pm0.3$ and $4.9\pm0.3$ over the volume of $54\times32\times32$ cMpc$^3$. The overdensity factor increases $2-3$ times when focusing on the high-density regions of scales $10-15$ cMpc. Interestingly, the HAE density maps reveal that BOSS1244 contains a dominant structure, while BOSS1542 manifests as a giant filamentary structure. We measure the H$\alpha$ luminosity functions (HLF), finding that BOSS1244's HLF is nearly identical to that of the general field at the same epoch, while BOSS1542 shows an excess of HAEs with high H$\alpha$ luminosity, indicating the presence of enhanced star formation or AGN activity. We conclude that the two massive MAMMOTH overdensities are undergoing a rapid galaxy mass assembly.


[24] 2009.08078

Photoelectric heating effects on the evolution of luminous disk galaxies

Photoelectric heating (PEH) influences the temperature and density of the interstellar medium (ISM), and potentially also affecting star formation. PEH is expected to have a stronger effect on massive galaxies, as they host larger dust reservoirs compared to dwarf systems. Accordingly, in this paper, we study PEH effects in Milky Way-like galaxies using smoothed particle hydrodynamics (SPH) code which self-consistently implements the evolution of the gas, dust, and interstellar radiation field (ISRF). Dust evolution includes dust formation by stars, destruction by SNe, and growth in dense media. We find that PEH suppresses star formation due to the excess heating that reduces the ISM density. This suppression is seen across the entire range of gas fractions, star formation recipes, dust models, and PEH efficiencies investigated by our code. The suppression ranges from negligible values to approximately a factor of five depending on the specific implementation. Galaxy models having higher gas fraction experience higher star formation suppression. The adopted dust model also alters the extent of star formation suppression. Moreover, when PEH is switched on, galaxy models show higher gas outflow rates and have higher loading factors indicative of enhanced SNe feedback. In gas-rich models (i.e. a gas fraction of 0.5), we also find that PEH suppresses the formation of disk clumps via violent disk instabilities, and thus suppresses bulge formation via clumps migration to the central regions.


[25] 2009.08080

On the Djorgovski-Gurzadyan dark energy integral equation and the Hubble diagram

We consider the observational aspects of the value of dark energy density from quantum vacuum fluctuations based initially on the Gurzadyan-Xue model. We reduce Djorgovski-Gurzadyan integral equation to a differential equation for the co-moving horizon and then, by means of the obtained explicit form for the luminosity distance, we construct the Hubble diagram for two classes of observational samples. For supernova and gamma-ray burst data we show that this approach provides viable predictions for distances up to $z \simeq 9$, quantitatively at least as good as the $\Lambda$CDM model does. The Hubble parameter dependence $H(z)$ of both models also reveals mutual crossing at $z=0.4018$, the interpretation of which seems less evident.


[26] 2009.08085

Vortex unpinning due to crustquake initiated neutron excitation and pulsar glitches

Pulsars undergoing crustquake release strain energy, which can be absorbed in a small region inside the inner crust of the star and excite the free superfluid neutrons therein. The scattering of these neutrons with the surrounding pinned vortices may unpin a large number of vortices and effectively reduce the pinning force on vortex lines. Such unpinning by neutron scattering can produce glitches for Crab like pulsars and Vela pulsar of size in the range $\sim 10^{-8} - 10^{-7}$, and $\sim 10^{-9} - 10^{-8}$, respectively. Although we discuss here the crustquake initiated excitation, the proposal is very generic and equally applicable for any other sources, which can excite the free superfluid neutrons, or can be responsible for superfluid - normal phase transition of neutron superfluid in the inner crust of a pulsar.


[27] 2009.08103

The Advanced Virgo Photon Calibrators

As the sensitivities of LIGO, Virgo and KAGRA detectors improve, calibration of the interferometers output is becoming more and more important and may impact scientific results. For the observing run O3, Virgo used for the first time photon calibrators (PCal) to calibrate the interferometer, using radiation pressure of a modulated auxiliary laser beam impinging on the Advanced Virgo end mirrors. Those optical devices, also used in LIGO, are now the calibration reference for the global gravitational wave detectors network. The intercalibration of LIGO and Virgo PCals, based on the same absolute reference called the Gold Standard, has allowed to remove a systematic bias of 3.92% that would have been present in Virgo calibration using the PCal. The uncertainty budget on the PCal-induced displacement of the end mirrors (NE and WE) of Advanced Virgo has been estimated to be 1.35% for O3a and 1.39% on NE PCal (resp. 1.73% on WE PCal) for O3b. This uncertainty is the limiting one for the global calibration of Advanced Virgo. It is expected to be reduced below 1% for the next observing runs.


[28] 2009.08121

Evidence of strong relationship between hemispheric asymmetry in solar coronal rotation and solar activity during solar cycle 24

In this article, we report an evidence of very high and statistically significant relationship between hemispheric asymmetry in solar coronal rotation rate and solar activity. Our approach is based on cross correlation of hemispheric asymmetry index (AI) in rotation rate with annual solar activity indicators. To obtain hemispheric asymmetry in solar rotation rate, we use solar full disc (SFD) images at 30.4 nm, 19.5 nm, and 28.4 nm wavelengths for 24th Solar Cycle i.e., for the period from 2008 to 2018, as recorded by the Solar Terrestrial Relations Observatory (STEREO) space mission. Our analysis shows that hemispheric asymmetry in rotation rate is high during the solar maxima from 2011 to 2014. On the other hand, hemispheric asymmetry drops gradually on both sides (i.e., from 2008 to 2011 and from 2014 to 2018). The results show that asymmetry index (AI) leads sunspot numbers by ~1.56 years. This gives a clear indication that hemispheric asymmetry triggers the formation of sunspots working together with the differential rotation of the Sun.


[29] 2009.08152

Resonant absorption: transformation of compressive motions into vortical motions

This paper investigates the changes in spatial properties when magnetohydrodynamic (MHD) waves undergo resonant damping in the Alfv\'en continuum. The analysis is carried out for a 1D cylindrical pressure-less plasma with a straight magnetic field. The effect of the damping on the spatial wave variables is determined by using complex frequencies that arise as a result of the resonant damping. Compression and vorticity are used to characterise the spatial evolution of the MHD wave. The most striking result is the huge spatial variation in the vorticity component parallel to the magnetic field. Parallel vorticity vanishes in the uniform part of the equilibrium. However, when the MHD wave moves into the non-uniform part, parallel vorticity explodes to values that are orders of magnitude higher than those attained by the transverse components in planes normal to the straight magnetic field. In the non-uniform part of the equilibrium plasma, the MHD wave is controlled by parallel vorticity and resembles an Alfv\'en wave, with the unfamiliar property that it has pressure variations even in the linear regime.


[30] 2009.08154

Confirming known planetary trends using a photometrically selected Kepler sample

Statistical studies of exoplanets and the properties of their host stars have been critical to informing models of planet formation. Numerous trends have arisen in particular from the rich \textit{Kepler} dataset, including that exoplanets are more likely to be found around stars with a high metallicity and the presence of a "gap" in the distribution of planetary radii at 1.9\,$R_\oplus$. Here we present a new analysis on the \textit{Kepler} field, using the APOGEE spectroscopic survey to build a metallicity calibration based on \textit{Gaia}, 2MASS and Str\"omgren photometry. This calibration, along with masses and radii derived from a Bayesian isochrone fitting algorithm, is used to test a number of these trends with unbiased, photometrically derived parameters, albeit with a smaller sample size in comparison to recent studies. We confirm that planets are indeed more frequently found around higher metallicity stars: planetary frequencies are $0.88\pm0.12$~percent for [Fe/H]\,<\,0 and $1.37\pm0.16$~percent for [Fe/H]\,$\geq$\,0. We also recover the planet radius gap, along with a slight positive correlation with stellar mass. We conclude that this method shows promise to derive robust statistic of exoplanets. We also remark that spectrophotometry from \textit{Gaia} DR3 will have an effective resolution similar to narrow band filters and allow to overcome the small sample size inherent in this study.


[31] 2009.08159

Ram pressure stripping of HI-rich galaxies infalling into massive clusters

We estimate the strength of ram pressure stripping (RPS) for HI-rich galaxies in X-ray detected clusters. We find that galaxies under stronger RPS tend to show more significantly reduced total HI mass and enhanced central SFR, compared to control galaxies in the field which have similar stellar mass, stellar surface density and integral star formation rate. Galaxies under strong or weak RPS account for around 40% of the HI-rich population at R200, and even beyond R200 in the most massive clusters. Our results imply the important role of RPS as a channel of environmental processing far before the galaxies reach the core region of clusters.


[32] 2009.08212

Galaxy and Mass Assembly: luminosity and stellar mass functions in GAMA groups

How do galaxy properties (such as stellar mass, luminosity, star formation rate, and morphology) and their evolution depend on the mass of their host dark matter halo? Using the Galaxy and Mass Assembly (GAMA) group catalogue, we address this question by exploring the dependence on host halo mass of the luminosity function (LF) and stellar mass function (SMF) for grouped galaxies subdivided by colour, morphology and central/satellite. We find that spheroidal galaxies in particular dominate the bright and massive ends of the LF and SMF, respectively. More massive haloes host more massive and more luminous central galaxies. The satellite LF and SMF respectively show a systematic brightening of characteristic magnitude, and increase in characteristic mass, with increasing halo mass. In contrast to some previous results, the faint-end and low-mass slopes show little systematic dependence on halo mass. Semi-analytic models and simulations show similar or enhanced dependence of central mass and luminosity on halo mass. Faint and low-mass simulated satellite galaxies are remarkably independent of halo mass, but the most massive satellites are more common in more massive groups. In the first investigation of low-redshift LF and SMF evolution in group environments, we find that the red/blue ratio of galaxies in groups has increased since redshift $z \approx 0.3$ relative to the field population. This observation strongly suggests that quenching of star formation in galaxies as they are accreted into galaxy groups is a significant and ongoing process.


[33] 2009.08220

Multi Frequency Temporal and Spectral variability study of Blazar PKS 1424-418

A study of blazar PKS 1424-418 was carried out using multi waveband data collected by Fermi-LAT, Swift-XRT, Swift-UVOT and SMARTS telescopes between MJD 56000 to MJD 56600 (14 Mar 2012 to 4 Nov 2013). Two flaring episodes were identified by analysing the gamma ray light curve. Simultaneous multi waveband Spectral Energy Distributions (SED) were obtained for those two flaring periods. A cross-correlation analysis of IR-Optical and $\gamma$-ray data suggested the origin of these emissions from the same region. We have set a lower limit for the Doppler factor using the highest energy photon observed from this source during the flaring periods, which should be $>$12. The broadband emission mechanism was studied by modelling the SED using leptonic emission mechanism.


[34] 2009.08224

Deep learning of galaxy cluster members through panchromatic HST imaging and extensive spectroscopy

The upcoming next-generation of extensive and data-intensive surveys are going to produce a vast amount of data, which can be efficiently dealt with Machine Learning methods to explore possible correlations within the multi-dimensional parameter space. We explored classification capabilities of Convolution Neural Networks (CNN) to identify galaxy Cluster Members (CLMs), by using Hubble Space Telescope images of 15 galaxy clusters at redshift 0.19


[35] 2009.08225

Comparative analysis of sky quality and meteorological variables during the total lunar eclipse on 14-15 April 2014 and their effect on qualitative measurements of the Bortle scale

A total lunar eclipse is plausible to have an influence on the variation of some environmental physical parameters, specifically on the conditions of the sky brightness, humidity and temperature. During the eclipse on 14$^{th}$-15$^{th}$ April 2014, these parameters were measured through a photometer and a weather station. The obtained results allow the comparison, practically, of the optimal conditions for observational astronomy work in the Tatacoa desert and therefore to certify it as suitable perfect place to develop night sky astronomical observations. This investigation determined, to some extent, the suitability of this place to carry out astronomical work and research within the optical range. Thus, the changes recorded during the astronomical phenomenon allowed the classification of the sky based on the Bortle Scale


[36] 2009.08231

The Pencil Code, a modular MPI code for partial differential equations and particles: multipurpose and multiuser-maintained

The Pencil Code is a highly modular physics-oriented simulation code that can be adapted to a wide range of applications. It is primarily designed to solve partial differential equations (PDEs) of compressible hydrodynamics and has lots of add-ons ranging from astrophysical magnetohydrodynamics (MHD) to meteorological cloud microphysics and engineering applications in combustion. Nevertheless, the framework is general and can also be applied to situations not related to hydrodynamics or even PDEs, for example when just the message passing interface or input/output strategies of the code are to be used. The code can also evolve Lagrangian (inertial and noninertial) particles, their coagulation and condensation, as well as their interaction with the fluid.


[37] 2009.08245

Type Ia Supernovae from wide white-dwarfs triples

For ultra-wide systems (with outer orbit >$10^{3}{\rm AU})$ the galactic field is collisional. Hence, ultra-wide triple white-dwarfs (TWDs) can be perturbed, by flyby stars, to sufficiently high outer eccentricity such that the triple becomes dynamically unstable. An unstable triple undergoes multiple binary-single resonant encounters between all three WDs. These encounters might result in a direct collision between any random two WDs and lead to a Type Ia supernova (SN) event. In case where the multiple resonant encounters did not produce a collision a compact binary is formed (while the third WD is ejected), this binary either collides or merges via gravitational wave emission, similar to the classic double-degenerate (DD) channel. In this research study we estimate the galactic rates of Type Ia SN from this channel to be $4\%-46\%$ and an addition of $1\%-10\%$ to the DD scenario.


[38] 2009.08247

Nonbinary Systems: Looking Towards the Future of Gender Equity in Planetary Science

Gender equity remains a major issue facing the field of planetary science, and there is broad interest in addressing gender disparities within space science and related disciplines. Many studies of these topics have been performed by professional planetary scientists who are relatively unfamiliar with research in fields such as gender studies and sociology. As a result, they adopt a normative view of gender as a binary choice of 'male' or 'female,' leaving planetary scientists whose genders do not fit within that model out of such research entirely. Reductive frameworks of gender and an overemphasis on quantification as an indicator of gendered phenomena are harmful to people of marginalized genders, especially those who live at the intersections of multiple axes of marginalization such as race, disability, and socioeconomic status. In order for the planetary science community to best serve its marginalized members as we move into the next decade, a new paradigm must be established. This paper aims to address the future of gender equity in planetary science by recommending better survey practices and institutional policies based on a more profound approach to gender.


[39] 2009.08268

NANOGrav Hints to Primordial Black Holes as Dark Matter

The NANOGrav Collaboration has recently published a strong evidence for a stochastic common-spectrum process that may be interpreted as a stochastic gravitational wave background. We show that such a signal can be explained by second-order gravitational waves produced during the formation of primordial black holes from the collapse of sizeable scalar perturbations generated during inflation. This possibility has two predictions: $i$) the primordial black holes may comprise the totality of the dark matter with the dominant contribution to their mass function falling in the range $(10^{-15}\div 10^{-11}) M_\odot$ and $ii$) the gravitational wave stochastic background will be seen as well by the LISA experiment.


[40] 2009.08272

Two New Nova Shells associated with V4362 Sagittarii and DO Aquilae

A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of 0.5p/m1.4 kpc for V4362 Sgr and 6.7 p/m 3.5 kpc -0.2 for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07``/year for DO Aql and 0.32``/year for V4362 Sgr. A preliminary investigation into the ionisation structure of the nova shell associated with V4362 Sgr is presented. The observed ionisation structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects.


[41] 2009.08300

Evolution of inspiralling neutron star binaries: effects of tidal interactions and orbital eccentricities

Neutron star (NS) binaries formed dynamically may have significant eccentricities while emitting gravitational waves (GWs) in the LIGO/VIRGO band. We study tidal effects in such eccentric inspiralling NS binaries using a set of hybrid equations. The NS is modelled as a compressible ellipsoid, which can deform nonlinearly due to tidal forces, while the orbit evolution is treated with the post-Newtonian (PN) theory up to 2.5-PN order. We find that in general, the tidal interaction can accelerate the inspiral, and cause orbital frequency and phase shifts. For circular inspirals, our calculations reproduce previous linear result at large binary separations, but incorporate the dynamical response of the NS at small separations. For eccentric inspirals, the frequency and phase shifts oscillate considerably near pericenter passages, and the oscillating amplitudes increase with eccentricities. As a result, the GW phase is also significantly influenced by the tidal effect. At merger, the cumulative GW phase shift can reach more than 10 radians (for typical NS mass $1.4M_\odot$ and radius 11.6 km), much larger than the circular inspiral case. Although the event rate of eccentric NS mergers is likely low, the detection of such mergers could provide a useful constraint on the NS equation of state.


[42] 2009.08301

Forward Modelling of MHD Waves in Braided Magnetic Fields

Aim. We investigate synthetic observational signatures generated from numerical models of transverse waves propagating in braided magnetic fields. Methods. We examine two simulations with different levels of magnetic field braiding and impose a periodic, transverse wave driver at the lower boundary. After waves reflect off the top boundary, a complex pattern of wave interference forms. We analyse the synthetic emission produced by the forward modelling code, FoMo. We examine line intensity, Doppler shifts and kinetic energy along several line-of-sight (LOS) angles. Results. The Doppler shifts showed the presence of transverse waves. However, when analysing the intensity, waves are less easily observed for more complex magnetic fields and may be mistaken for background noise. Depending on the LOS angle, the observable signatures of waves reflect some of the magnetic field braiding, particularly when multiple emission lines are available. In the more braided simulation, signatures of phase mixing can be identified. We identify possible ambiguities in the interpretation of wave modes based on the synthetic emission signatures. Conclusions. Most of the observables within this article behave as expected, given knowledge of the evolution of the parameters in 3D space. However, some intriguing observational signatures are present. Detecting regions of magnetic field complexity is somewhat possible when waves are present. However, simultaneous spectroscopic imaging from different lines is important to identify these locations. Care needs to be taken when interpreting intensity and Doppler velocity signatures as torsional motions as, in our setup, such signatures were a consequence of the magnetic field complexity and not torsional waves. Finally, the kinetic energy, estimated with Doppler velocities, is dependent on the polarisation of the wave, complexity of the background field and the LOS.


[43] 2009.08306

Geometrical observational bounds on a fractal horizon holographic dark energy

A novel fractal structure for the cosmological horizon, inspired by COVID-19 geometry, which results in a modified area entropy, is applied to cosmology in order to serve dark energy. The constraints based on a complete set of observational data are derived. There is a strong Bayesian evidence in favor of such a dark energy in comparison to a standard $\Lambda$CDM model and that this energy cannot be reduced to a cosmological constant. Besides, there is a shift towards smaller values of baryon density parameter and towards larger values of the Hubble parameter, which reduces the Hubble tension.


[44] 2009.08307

Flight in the Jovian Stratosphere. Engine Concept and Flight Altitude Determination

An effective method for detailed observation of the Solar System planets is the use of vehicles that can perform flight in their atmospheres, with the most promising of them being Flyers (aircraft for other planets atmospheres). Besides the advantage of probing the atmosphere directly, they have the ability to fly on selected direction and altitude, making them suitable for collecting information over large areas. Equipping the Flyer with nuclear propulsion will allow it to conduct flight for months without the need of combustible fuel or oxidizer to be carried on board. Among the planets of the Solar System and their satellites, Jupiter is a viable target for exploration, since it features thick atmosphere suitable for aerodynamic flight, there is no solid surface that can be contaminated after end of the mission, and the atmospheric data for designing a Flyer is readily available. This paper proposes a mathematical model for evaluating the thrust, the lift and the maximum allowable mass for horizontal steady flight as functions of the altitude and different heat chamber temperatures.


[45] 2009.08312

White Paper on Improvements to the NASA Research and Analysis Proposal and Review System

We review some key issues pertaining to NASA's Research and Analysis programs, and offer recommended actions to mitigate or resolve these issues. In particular, we recommended that NASA increases funding to support a healthy selection rate (~40%) for R&A programs, which underpin much scientific discovery with NASA mission data, and on which the majority of the U.S. planetary science community relies (either in part or wholly). We also recommend additional actions NASA can take to ensure a more equitable and sustainable planetary science research community in the U.S., including supporting the next generations of planetary researchers, working to minimize biases in peer review, and reducing the burden of scientists as they prepare R&A proposals.


[46] 2009.08336

Getting the model right; an information criterion for spectroscopy

Robust model-fitting to spectroscopic transitions is a requirement across many fields of science. The corrected Akaike and Bayesian information criteria (AICc and BIC) are most frequently used to select the optimal number of fitting parameters. In general, AICc modelling is thought to overfit (too many model parameters) and BIC underfits. For spectroscopic modelling, both AICc and BIC lack in two important respects: (a) no penalty distinction is made according to line strength such that parameters of weak lines close to the detection threshold are treated with equal importance as strong lines and (b) no account is taken of the way in which spectral lines impact on narrow data regions. In this paper we introduce a new information criterion that addresses these shortcomings, the "Spectral Information Criterion" (SpIC). Spectral simulations are used to compare performances. The main findings are (i) SpIC clearly outperforms AICc for high signal to noise data, (ii) SpIC and AICc work equally well for lower signal to noise data, although SpIC achieves this with fewer parameters, and (iii) BIC does not perform well (for this application) and should be avoided. The new method should be of broader applicability (beyond spectroscopy), wherever different model parameters influence separated small ranges within a larger dataset and/or have widely varying sensitivities.


[47] 2009.08338

A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776

We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776, J=8.5mag, M=0.54+-0.03Msun) detected during Sector 10 observations of the Transiting Exoplanet Survey Satellite (TESS). Combining them with HARPS radial velocities, as well as ground-based follow-up transit observations from MEarth and LCOGT telescopes, we measured for the inner planet, TOI-776b, a period of 8.25d, a radius of 1.83+-0.11Re, and a mass of 4.66+-0.97Me; and for the outer planet, TOI-776c, a period of 15.66d, a radius of 2.06+-0.13Re, and a mass of 6.1+-1.5Me. The Doppler data shows one additional signal, with a period of 35d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54Msun. Due to the brightness of the star, the TOI-776 system is also an excellent target for the JWST, providing a remarkable laboratory to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.


[48] 2009.08350

nazgul: A statistical approach to gamma-ray burst localization. Triangulation via non-stationary time-series models

Context. Gamma-ray bursts can be located via arrival time signal triangulation using gamma-ray detectors in orbit throughout the solar system. The classical approach based on cross-correlations of binned light curves ignores the Poisson nature of the time-series data, and is unable to model the full complexity of the problem. Aims. To present a statistically proper and robust GRB timing/triangulation algorithm as a modern update to the original procedures used for the Interplanetary Network (IPN). Methods. A hierarchical Bayesian forward model for the unknown temporal signal evolution is learned via random Fourier features (RFF) and fitted to each detector's time-series data with time-differences that correspond to GRB's position on the sky via the appropriate Poisson likelihood. Results. Our novel method can robustly estimate the position of a GRB as verified via simulations. The uncertainties generated by the method are robust and in many cases more precise compared to the classical method. Thus, we have a method that can become a valuable tool for gravitational wave follow-up. All software and analysis scripts are made publicly available here (https://github.com/grburgess/nazgul) for the purpose of replication.


[49] 2009.08383

The EDGE-CALIFA survey: exploring the role of the molecular gas on the galaxy star formation quenching

Understanding how galaxies cease to form stars represents an outstanding challenge for galaxy evolution theories. This process of "star formation quenching" has been related to various causes, including Active Galactic Nuclei (AGN) activity, the influence of large-scale dynamics, and the environment in which galaxies live. In this paper, we present the first results from a follow-up of CALIFA survey galaxies with observations of molecular gas obtained with the APEX telescope. Together with EDGE survey CARMA observations, we collect $^{12}$CO observations that cover approximately one effective radius in 472 CALIFA galaxies. We observe that the deficit of galaxy star formation with respect to the star formation main sequence (SFMS) increases with the absence of molecular gas and with a reduced efficiency of conversion of molecular gas into stars, in line with results of other integrated studies. However, by dividing the sample into galaxies dominated by star formation and galaxies quenched in their centres (as indicated by the average value of the H$\alpha$ equivalent width), we find that this deficit increases sharply once a certain level of gas consumption is reached, indicating that different mechanisms drive separation from the SFMS in star-forming and quenched galaxies. Our results indicate that differences in the amount of molecular gas at a fixed stellar mass are the primary driver for the dispersion in the SFMS, and the most likely explanation for the start of star-formation quenching. However, once a galaxy is quenched, changes in star formation efficiency drive how much a retired galaxy separates in star formation rate from star-forming ones of similar masses. In other words, once a paucity of molecular gas has significantly reduced star formation, changes in the star formation efficiency are what drives a galaxy deeper into the red cloud, retiring it.


[50] 2009.08396

Feasibility Analysis and Preliminary Design of ChipSat Entry for In-situ Investigation of the Atmosphere of Venus

Recent miniaturization of electronics in very small, low-cost and low-power configurations suitable for use in spacecraft have inspired innovative small-scale satellite concepts, such as ChipSats, centimeter-scale satellites with a mass of a few grams. These extremely small spacecraft have the potential to usher in a new age of space science accessibility. Due to their low ballistic coefficient, ChipSats can potentially be used in a swarm constellation for extended surveys of planetary atmospheres, providing large amounts of data with high reliability and redundancy. We present a preliminary feasibility analysis of a ChipSat planetary atmospheric entry mission with the purpose of searching for traces of microscopic lifeforms in the atmosphere of Venus. Indeed, the lower cloud layer of the Venusian atmosphere could be a good target for searching for microbial lifeforms, due to the favourable atmospheric conditions and the presence of micron-sized sulfuric acid aerosols. A numerical model simulating the planetary entry of a spacecraft of specified geometry, applicable to any atmosphere for which sufficient atmospheric data are available, is implemented and verified. The results are used to create a high-level design of a ChipSat mission cruising in the Venusian atmosphere at altitudes favorable for the existence of life. The paper discusses the ChipSat mission concept and considerations about the spacecraft preliminary design at system level, including the selection of a potential payload.


[51] 2009.08397

High-energy gamma-ray study of the dynamically young SNR G150.3+4.5

The supernova remnant (SNR) G150.3+4.5 was recently discovered in the radio band; it exhibits a shell-like morphology with an angular size of $\sim 3^{\circ}$, suggesting either an old or a nearby SNR. Extended $\gamma$-ray emission spatially coincident with the SNR was reported in the Fermi Galactic Extended Source Catalog, with a power-law spectral index of $\Gamma$ = 1.91 $\pm$ 0.09. Studying particle acceleration in SNRs through their $\gamma$-ray emission is of primary concern to assess the nature of accelerated particles and the maximum energy they can reach. Using more than ten years of Fermi-LAT data, we investigate the morphological and spectral properties of the SNR G150.3+4.5 from 300 MeV to 3 TeV. We use the latest releases of the Fermi-LAT catalog, the instrument response functions and the Galactic and isotropic diffuse emissions. We use ROSAT all-sky survey data to assess any thermal and nonthermal X-ray emission, and we derive minimum and maximum distance to G150.3+4.5. We describe the $\gamma$-ray emission of G150.3+4.5 by an extended component which is found to be spatially coincident with the radio SNR. The spectrum is hard and the detection of photons up to hundreds of GeV points towards an emission from a dynamically young SNR. The lack of X-ray emission gives a tight constraint on the ambient density $n_0 \leq 3.6 \times 10^{-3}$ cm$^{-3}$. Since G150.3+4.5 is not reported as a historical SNR, we impose a lower limit on its age of $t$ = 1 kyr. We estimate its distance to be between 0.7 and 4.5 kpc. We find that G150.3+4.5 is spectrally similar to other dynamically young and shell-type SNRs, such as RX J1713.7$-$3946 or Vela Junior. The broadband nonthermal emission is explained with a leptonic scenario, implying a downstream magnetic field of $B = 5$ $\mu$G and acceleration of particles up to few TeV energies.


[52] 2009.08400

Solar Flare Energy Partitioning and Transport -- the Impulsive Phase (a Heliophysics 2050 White Paper)

Solar flares are a fundamental component of solar eruptive events (SEEs; along with solar energetic particles, SEPs, and coronal mass ejections, CMEs). Flares are the first component of the SEE to impact our atmosphere, which can set the stage for the arrival of the associated SEPs and CME. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. To explain and ultimately predict these geoeffective events, the heliophysics community requires a comprehensive understanding of the processes that transform and distribute stored magnetic energy into other forms, including the broadband radiative enhancement that characterises flares. This white paper, submitted to the Heliophysics 2050 Workshop, discusses the flare impulsive phase part of SEEs, setting out the questions that need addressing via a combination of theoretical, modelling, and observational research. In short, by 2050 we must determine the mechanisms of particle acceleration and propagation, and must push beyond the paradigm of energy transport via nonthermal electron beams, to also account for accelerated protons & ions and downward directed Alfven waves.


[53] 2009.08402

Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C--D Band Strengths of Mono-Deuterated Species

Deuterium (D) is one of the light elements created in the big bang. As the Galaxy evolves, the D/H abundance in the interstellar medium (ISM) decreases from its primordial value due to "astration". However, the observed gas-phase D/H abundances of some interstellar sightlines are substantially lower than the expected reduction by astration alone. The missing D could have been depleted onto polycyclic aromatic hydrocarbon (PAH) molecules which are ubiquitous and abundant in interstellar regions. To quantitatively explore the hypothesis of PAHs as a possible reservoir of interstellar D, we compute quantum-chemically the infrared vibrational spectra of mono-deuterated PAHs (and their cations) of various sizes. We find that, as expected, when H in PAHs is replaced by D, the C-H stretching and bending modes at 3.3, 8.6 and 11.3 $\mu$m respectively shift to longer wavelengths at $\sim$4.4, 11.4 and 15.4 $\mu$m by a factor of $\sim$$\sqrt{13/7}$, the difference in reduced mass between the C-H and C-D oscillators. We derive from the computed spectra the mean intrinsic strengths of the 3.3 $\mu$m C-H stretch and 4.4 $\mu$m C--D stretch to be $\langle A_{3.3} \rangle \sim 13.4$ km/mol and $\langle A_{4.4} \rangle \sim 7.4$ km/mol for neutral deuterated PAHs which would dominate the interstellar 3.3 and 4.4 $\mu$m emission. By comparing the computationally-derived mean ratio of $\langle A_{4.4}/A_{3.3} \rangle \sim 0.56$ for neutral PAHs with the mean ratio of the observed intensities of $\langle (I_{4.4}/I_{3.3})_{\rm obs} \rangle \sim 0.019$, we estimate the degree of deuteration (i.e., the fraction of peripheral atoms attached to C in the form of D) to be ~2.4\%, corresponding to a D-enrichment of a factor of ~1200 with respect to the interstellar D/H abundance.


[54] 2009.08406

On the Absorption Properties of Metallic Needles

Needle-like metallic particles have been suggested to explain a wide variety of astrophysical phenomena, ranging from the mid-infrared interstellar extinction to the thermalization of starlight to generate the cosmic microwave background. These suggestions rely on the amplitude and the wavelength dependence of the absorption cross sections of metallic needles. On the absence of an exact solution to the absorption properties of metallic needles, their absorption cross sections are often derived from the antenna approximation. However, it is shown here that the antenna approximation is not an appropriate representation since it violates the Kramers-Kronig relation. Stimulated by the recent discovery of iron whiskers in asteroid Itokawa and graphite whiskers in carbonaceous chondrites, we call for rigorous calculations of the absorption cross sections of metallic needle-like particles, presumably with the discrete dipole approximation. We also call for experimental studies of the formation and growth mechanisms of metallic needle-like particles as well as experimental measurements of the absorption cross sections of metallic needles of various aspect ratios over a wide wavelength range to bound theoretical calculations.


[55] 2009.08407

Solar Flare Energy Partitioning and Transport -- the Gradual Phase (a Heliophysics 2050 White Paper)

Solar flares are a fundamental component of solar eruptive events (SEEs; along with solar energetic particles, SEPs, and coronal mass ejections, CMEs). Flares are the first component of the SEE to impact our atmosphere, which can set the stage for the arrival of the associated SEPs and CME. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. To explain and ultimately predict these geoeffective events, the heliophysics community requires a comprehensive understanding of the processes that transform and distribute stored magnetic energy into other forms, including the broadband radiative enhancement that characterises flares. This white paper, submitted to the Heliophysics 2050 Workshop, discusses the flare gradual phase part of SEEs, setting out the questions that need addressing via a combination of theoretical, modelling, and observational research. In short, the flare gradual phase persists much longer than predicted so, by 2050, we must identify the characteristics of the significant energy deposition sustaining the gradual phase, and address the fundamental processes of turbulence and non-local heat flux.


[56] 2009.08409

Evaluating Low-Frequency Pulsar Observations to Monitor Dispersion with the Giant Metrewave Radio Telescope

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project has the primary goal of detecting and characterizing low-frequency gravitational waves through high-precision pulsar timing. The mitigation of interstellar effects is crucial to achieve the necessary precision for gravitational wave detection. Effects like dispersion and scattering are more influential at lower observing frequencies, with the variation of these quantities over week-month timescales requiring high-cadence multi-frequency observations for pulsar timing projects. In this work, we utilize the dual-frequency observing capability of the Giant Metrewave Radio Telescope (GMRT) and evaluate the potential decrease in dispersion measure (DM) uncertainties when combined with existing pulsar timing array data. We present the timing analysis for four millisecond pulsars observed with the GMRT simultaneously at 322 and 607 MHz, and compare the DM measurements with those obtained through NANOGrav observations with the Green Bank Telescope (GBT) and Arecibo Observatory at 1400 to 2300 MHz frequencies. Measured DM values with the GMRT and NANOGrav program show significant offsets for some pulsars, which could be caused by pulse profile evolution in the two frequency bands. In comparison to the predicted DM uncertainties when incorporating these low-frequency data into the NANOGrav dataset, we find that higher-precision GMRT data is necessary to provide improved DM measurements. Through the detection and analysis of pulse profile baseline ripple in data on test pulsar B1929+10, we find that, while not important for this data, it may be relevant for other timing datasets. We discuss the possible advantages and challenges of incorporating GMRT data into NANOGrav and International Pulsar Timing Array datasets.


[57] 2009.08423

Constraining the orientation of the spin axes of extrasolar minor bodies 1I/2017 U1 (`Oumuamua) and 2I/Borisov

Context. The orientation of the spin axis of a comet is defined by the values of its equatorial obliquity and its cometocentric longitude of the Sun. These parameters can be computed from the components of the non-gravitational force caused by outgassing, if the cometary activity is well characterized. The trajectories of known interstellar bodies passing through the solar system show non-gravitational accelerations. Aims. The spin-axis orientation of 1I/2017 U1 (`Oumuamua) remains to be determined; for 2I/Borisov, the already released results are mutually exclusive. Here, we investigate the orientation of the spin axes of `Oumuamua and 2I/Borisov using public orbit determinations that consider outgassing. Methods. We applied the Monte Carlo using the Covariance Matrix method together with Monte Carlo random search techniques to compute the distributions of equatorial obliquities and cometocentric longitudes of the Sun at perihelion of `Oumuamua and 2I/Borisov from the values of the non-gravitational parameters. Results. We found that the equatorial obliquity of `Oumuamua could be about 93 deg, if it has a very prolate (fusiform) shape, or close to 16 deg, if it is very oblate (disk-like). Different orbit determinations of 2I/Borisov gave values of 59 deg and 90 deg for its obliquity. The distributions of cometocentric longitudes were in general multimodal. Conclusions. The most probable spin-axis direction of `Oumuamua in equatorial coordinates could be (280 degrees, +46 degrees) if very prolate or (312 deg, -50 deg) if very oblate. For the orbit determinations of 2I/Borisov used here, we find most probable poles pointing near (275 deg, +65 deg) and (231 deg, +30 deg), respectively. Although our analysis favors an oblate shape for 2I/Borisov, a prolate one cannot be ruled out.


[58] 2009.08446

VALES VII: Molecular and ionized gas properties in pressure balanced interstellar medium of starburst galaxies at z ~ 0.15

Context. Spatially resolved observations of the ionized and molecular gas are critical for understanding the physical processes that govern the interstellar medium (ISM) in galaxies. Aims. To study the morpho-kinematic properties of the ionized and molecular gas in three dusty starburst galaxies at $z = 0.12-0.17$ to explore the relation between molecular ISM gas phase dynamics and the star-formation activity. Methods. We analyse $\sim$kpc-scale ALMA CO(1--0) and seeing limited SINFONI Paschen-$\alpha$ observations. We use a dynamical mass model, which accounts for beam-smearing effects, to constrain the CO-to-H$_2$ conversion factor. Results. One starburst galaxy shows irregular morphology which may indicate a major merger, while the other two systems show disc-like morpho-kinematics. The two disc-like starbursts show molecular gas velocity dispersion values comparable with that seen in local LIRG/ULIRGs, but in an ISM with molecular gas fraction and surface density values consistent to that reported for local star-forming galaxies. These molecular gas velocity dispersion values can be explained by assuming vertical pressure equilibrium. The star-formation activity is correlated with the molecular gas content suggesting depletion times of the order of $\sim 0.1-1$ Gyr. The star formation rate surface density ($\Sigma_{\rm SFR}$) correlates with the ISM pressure set by self-gravity ($P_{\rm grav}$) following a power law with an exponent close to 0.8. Conclusions. In dusty disc-like starburst galaxies, our data support the scenario in which the molecular gas velocity dispersion values are driven by the ISM pressure set by self-gravity, responsible to maintain the vertical pressure balance. The correlation between $\Sigma_{\rm SFR}$ and $P_{\rm grav}$ suggests that, in these dusty starbursts galaxies, the star formation activity arises as a consequence of the ISM pressure balance.


[59] 2009.08455

Recombination-independent determination of the sound horizon and the Hubble constant from BAO

The Hubble tension and attempts to resolve it by modifying the physics of (or at) recombination motivate finding ways to determine $H_0$ and the sound horizon at the epoch of baryon decoupling $r_{\rm d}$ in ways that neither rely on a recombination model nor on late-time Hubble data. In this work, we investigate what one can learn from the current and future BAO data when treating $r_{\rm d}$ and $H_0$ as independent free parameters. It is well known that BAO gives exquisite constraints on the product $r_{\rm d}H_0$. We show here that imposing a moderate prior on $\Omega_{\rm m} h^2$ breaks the degeneracy between $r_{\rm d}$ and $H_0$. Using the latest BAO data, including the recently released eBOSS DR16, along with a $\Omega_{\rm m} h^2$ prior based on the Planck best fit $\Lambda$CDM model, we find $r_{\rm d} =143.7 \pm 2.7$ Mpc and $H_0 = 69.6 \pm 1.8$ km/s/Mpc. BAO data therefore prefers somewhat lower $r_{\rm d}$ and higher $H_0$ than those inferred from Planck data in a $\Lambda$CDM model. We find similar values when combing BAO with the Pantheon supernovae, DES galaxy weak lensing, Planck or SPTPol CMB lensing and the cosmic chronometers data. We perform a forecast for DESI and find that, when aided with a moderate prior on $\Omega_{\rm m} h^2$, DESI will measure $r_{\rm d}$ and $H_0$ without assuming a recombination model with an accuracy surpassing the current best estimates from Planck.


[60] 2009.07294

Baryogenesis from the weak scale to the GUT scale

We review the current status of baryogenesis with emphasis on electroweak baryogenesis and leptogenesis. The first detailed studies were carried out for SU(5) GUT models where CP-violating decays of leptoquarks generate a baryon asymmetry. These GUT models were excluded by the discovery of B+L violating sphaleron processes at high temperatures. Yet a new possibility emerged, electroweak baryogenesis. Here sphaleron processes generate a baryon asymmetry during a strongly first-order phase transition. This mechanism has been studied in many extensions of the Standard Model. However, constraints from the LHC and from low-energy precision experiments exclude most of the known models, leaving composite Higgs models of electroweak symmetry breaking as an interesting possibility. Sphaleron processes are also the basis of leptogenesis, where CP-violating decays of heavy right-handed neutrinos generate a lepton asymmetry which is partially converted to a baryon asymmetry. This mechanism is closely related to the one of GUT baryogenesis, and simple estimates based on GUT models can explain the order of magnitude of the observed baryon-to-photon ratio. In the one-flavour approximation an upper bound on the light neutrino masses has been derived which is consistent with the cosmological upper bound on the sum of neutrino masses. For quasi-degenerate right-handed neutrinos the leptogenesis temperature can be lowered from the GUT scale down to the weak scale, and CP-violating oscillations of GeV sterile neutinos can also lead to successfull leptogenesis. Significant progress has been made in developing a full field theoretical description of thermal leptogenesis, which demonstrated that interactions with gauge bosons of the thermal plasma play a crucial role. Finally, we discuss recent ideas how the seesaw mechanism and B-L breaking at the GUT scale can be probed by gravitational waves.


[61] 2009.07852

Unraveling the Dirac Neutrino with Cosmological and Terrestrial Detectors

We propose a method for testing the Dirac neutrino hypothesis by combining data from terrestrial neutrino experiments, such as tritium beta decay, with data from cosmological observations, such as the cosmic microwave background and large scale structure surveys. If the neutrinos are Dirac particles, and if the active neutrinos' sterile partners were once thermalized in the early universe, then this new cosmological relic would simultaneously contribute to the effective number of relativistic species, $N_\text{eff}$, and also lead to a mismatch between the cosmologically-measured effective neutrino mass sum $\Sigma m_\nu$ and the terrestrially-measured active neutrino mass sum $\Sigma_i m_i$. We point out that specifically correlated deviations in $N_\text{eff} \gtrsim 3$ and $\Sigma m_\nu \gtrsim \Sigma_i m_i$ above their standard predictions could be the harbinger revealing the Dirac nature of neutrinos. We provide several benchmark examples, including Dirac leptogenesis, that predict a thermal relic population of the sterile partners, and we discuss the relevant observational prospects with current and near-future experiments. This work provides a novel approach to probe an important possibility of the origin of neutrino mass.


[62] 2009.07915

A semi-analytical solution to the maximum likelihood fit of Poisson data to a linear model using the Cash statistic

[ABRIDGED] The Cash statistic, also known as the C stat, is commonly used for the analysis of low-count Poisson data, including data with null counts for certain values of the independent variable. The use of this statistic is especially attractive for low-count data that cannot be combined, or re-binned, without loss of resolution. This paper presents a new maximum-likelihood solution for the best-fit parameters of a linear model using the Poisson-based Cash statistic. The solution presented in this paper provides a new and simple method to measure the best-fit parameters of a linear model for any Poisson-based data, including data with null counts. In particular, the method enforces the requirement that the best-fit linear model be non-negative throughout the support of the independent variable. The method is summarized in a simple algorithm to fit Poisson counting data of any size and counting rate with a linear model, by-passing entirely the use of the traditional $\chi^2$ statistic.


[63] 2009.08001

Fluid pulsation modes from strange stars in a higher-dimensional space-time

In this work, we make the first step to derive non-radial pulsation equations in extra dimensions and investigate how the $f$- and $p_1$-mode frequencies of strange quark stars, within the Cowling approximation, change with the number of dimensions. In this regard, the study is performed by solving numerically the non-radial pulsation equations, adjusted for a $d$-dimensional space-time $(d\geq4)$. We connect the interior to a Schwarzschild-Tangherlini exterior metric and analyze the $f$- and $p_1$- mode frequencies. We found that the frequencies could become higher than those found in four-dimensional space-time. The $f$-mode frequency is essentially constant and only for large gravitational radius values grows monotonically and fast with the gravitational radius. In a gravitational radius range, where $f$-mode frequencies are constant, they increase for space-time dimensions $4\leq d\leq6$ and decrease for $d\geq7$. Regarding $p_1$-mode frequencies they are always larger for higher dimensions and decay monotonically with the increase of the gravitational radius. In extra dimensions, as it happens for four-dimensional space-time, we found $p_1$-mode frequencies are always larger than the $f$-modes ones. In the Newtonian gravity, for a homogeneous star in $d$ dimensions, we observe that the $f$-mode eigenfrequencies are constant and given by the relation $\omega^2=l\, M\, G_d/R^{d-1}$; where $l$ represents the spherical harmonic index, $M\,G_d$ being the total star mass and $R$ the stellar radius.


[64] 2009.08086

Gravitational wave echoes induced by a point mass plunging to a black hole

Recently, the possibility of detecting gravitational wave echoes in the data stream subsequent to the binary black hole mergers observed by LIGO was suggested. Motivated by this suggestion, we presented a templates of echoes based on black hole perturbations in our previous work. There, we assumed that the incident waves resulting in echoes are similar to the ones that directly escape to the asymptotic infinity. In this work, to obtain more plausible guess on the waveform of echoes removing the naive assumption on the incident waves, we investigate gravitational waves induced by a point mass plunging into a Kerr black hole. We solve the linear perturbation equation sourced by the plunging mass under the purely outgoing boundary condition at infinity and a reflection boundary condition near the horizon. We find that the low frequency component below the threshold of the super-radiant instability is highly suppressed, which is consistent with the incident waveform assumed in the previous analysis. We also find that the high frequency mode excitation is significantly larger than the one used in the previous analysis, if we adopt the perfectly reflective boundary condition independently of the frequency. When we use a simple template in which the same waveform as the direct emissions to infinity is repeated with the decreasing amplitude, the correlation between the expected signal and the template turns out to decrease very rapidly.


[65] 2009.08104

Bounds on neutrino-scalar non-standard interactions from big bang nucleosynthesis

Coherent forward scattering processes by neutrino-scalar non-standard interactions (SNSI) induce an effective neutrino mass. In the Early Universe, a large neutrino effective mass restricts the production of neutrinos. The SNSI effect is modulated by two effective couplings, these account for the coupling between neutrinos and electrons/positrons, $G_{\rm eff}$, and the neutrino self-interaction, $G_{\rm S}$. These parameters are directly related to the effective number of relativistic species and non-zero values imply a smaller than expected $N_{\rm eff}$. We employ big bang nucleosynthesis to constraint the SNSI effect. We find that $ G_{\rm eff }< 3.8$ MeV$^{-2}$ and $ G_{\rm S }< 6.2 \times 10^{7}$ MeV$^{-2}$ at 95\% CL. For a scalar mass in the range $10^{-15} {\rm eV}\lesssim m_{\phi}\lesssim 10^{-5}{\rm eV}$, our neutrino-scalar coupling constraint is more restrictive than any previous result.


[66] 2009.08163

A numerical stability analysis for the Einstein-Vlasov system

We investigate stability issues for steady states of the spherically symmetric Einstein-Vlasov system numerically in Schwarzschild, maximal areal, and Eddington-Finkelstein coordinates. Across all coordinate systems we confirm the conjecture that the first binding energy maximum along a one-parameter family of steady states signals the onset of instability. Beyond this maximum perturbed solutions either collapse to a black hole, form heteroclinic orbits, or eventually fully disperse. Contrary to earlier research, we find that a negative binding energy does not necessarily correspond to fully dispersing solutions. We also comment on the so-called turning point principle from the viewpoint of our numerical results. The physical reliability of the latter is strengthened by obtaining consistent results in the three different coordinate systems and by the systematic use of dynamically accessible perturbations.