adsabs/SciX_UAT_keywords huggingface dataset:
Analyzing the Galactic Pulsar Distribution with Machine Learning

We explore the possibility of inferring the properties of the Galactic population of neutron stars through machine learning. In particular, in this paper we focus on their dynamical characteristics and show that an artificial neural network is able to estimate with high accuracy the parameters that control the current positions of a mock population of pulsars. For this purpose, we implement a simplified population-synthesis framework (where selection biases are neglected at this stage) and concentrate on the natal kick-velocity distribution and the distribution of birth distances from the Galactic plane. By varying these and evolving the pulsar trajectories in time, we generate a series of simulations that are used to train and validate a suitably structured convolutional neural network. We demonstrate that our network is able to recover the parameters governing the distribution of kick velocity and Galactic height with a mean relative error of about 10-2. We discuss the limitations of our idealized approach and study a toy problem to introduce selection effects in a phenomenological way by incorporating the observed proper motions of 216 isolated pulsars. Our analysis highlights that by increasing the sample of pulsars with accurate proper-motion measurements by a factor of ~10, one of the future breakthroughs of the Square Kilometre Array, we might succeed in constraining the birth spatial and kick-velocity distribution of the neutron stars in the Milky Way with high precision through machine learning.

Keywords: neutron stars; pulsars; convolutional neural networks; proper motions; neural networks
CO Survey of High-z Radio Galaxies, Revisited with the Atacama Large Millimeter/submillimeter Array: Jet-Cloud Alignments and Synchrotron Brightening by Molecular Gas in the Circumgalactic Environment

Powerful radio sources associated with supermassive black holes are among the most luminous objects in the universe, and are frequently recognized both as cosmological probes and active constituents in the evolution of galaxies. We present alignments between radio jets and cold molecular gas in the environment of distant radio galaxies, and show that the brightness of the radio synchrotron source can be enhanced by its interplay with the molecular gas. Our work is based on CO J > 1 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of three radio galaxies with redshifts in the range 1.4 < z < 2.1, namely MRC 0114-211 (z = 1.41), MRC 0156-252 (z = 2.02), and MRC 2048-272 (z = 2.05). These ALMA observations support previous work that found molecular gas out to 50 kpc in the circumgalactic environment, based on a CO(1-0) survey performed with the Australia Telescope Compact Array. The CO emission is found along the radio axes but beyond the main radio lobes. When compared to a large sample of high-z radio galaxies from the literature, we find that the presence of this cold molecular medium correlates with an increased flux-density ratio of the main versus counter-lobe. This suggest that the radio lobe brightens when encountering cold molecular gas in the environment. While part of the molecular gas is likely related to the interstellar medium from either the host or a companion galaxy, a significant fraction of the molecular gas in these systems shows very low excitation, with r 2-1/1-0 and r 3-2/1-0 values ≲0.2. This could be part of the circumgalactic medium.

Keywords: high-redshift galaxies; radio galaxies; radio jets; radio loud quasars; ultraluminous infrared galaxies; galaxy environments; circumgalactic medium; radio astrometry; millimeter astronomy; submillimeter astronomy; intracluster medium; protoclusters
ALMA Evidence for Ram Pressure Compression and Stripping of Molecular Gas in the Virgo Cluster Galaxy NGC 4402

High-resolution (1″ × 2″) Atacama Large Millimeter Array CO(2-1) observations of the ram pressure stripped galaxy NGC 4402 in the Virgo cluster show some of the clearest evidence yet for the impacts of ram pressure on the molecular interstellar medium (ISM) of a galaxy. The eastern side of the galaxy at r ∼ 4.5 kpc, upon which ram pressure is incident, has a large (width ∼1 kpc, height ∼1 kpc above the disk midplane) extraplanar plume of molecular gas and dust. Molecular gas in the plume region shows distinct noncircular motions in the direction of the ram pressure; the kinematic offset of up to 60 km s-1 is consistent with acceleration by ram pressure. We also detect a small amount of gas in clouds below the plume that are spatially and kinematically distinct from the surrounding medium, and appear to be decoupled from the stripped ISM. We propose that diffuse molecular gas is directly stripped but giant molecular cloud (GMC) density gas is not directly stripped, and so decouples from lower density stripped gas. However, GMCs become effectively stripped on short timescales. We also find morphological and kinematic signatures of ram pressure compression of molecular gas in a region of intense star formation on the leading side at r ∼ 3.5 kpc. We propose that the compressed and stripped zones represent different evolutionary stages of the ram pressure interaction, and that feedback from star formation in the compressed zone facilitates the effective stripping of GMCs by making the gas cycle rapidly to a lower density diffuse state.

Keywords: galaxy evolution; interstellar medium; molecular gas; diffuse molecular clouds; giant molecular clouds; virgo cluster; galaxy clusters
A Machine-learning Approach to Enhancing eROSITA Observations

The eROSITA X-ray telescope, launched in 2019, is predicted to observe roughly 100,000 galaxy clusters. Follow-up observations of these clusters from Chandra, for example, will be needed to resolve outstanding questions about galaxy cluster physics. Deep Chandra cluster observations are expensive, and it is unfeasible to follow up every eROSITA cluster, therefore the objects that are chosen for follow-up must be chosen with care. To address this, we have developed an algorithm for predicting longer-duration, background-free observations, based on mock eROSITA observations. We make use of the hydrodynamic cosmological simulation Magneticum, simulate eROSITA instrument conditions using SIXTE, and apply a novel convolutional neural network to output a deep Chandra-like "super observation" of each cluster in our simulation sample. Any follow-up merit assessment tool should be designed with a specific use case in mind; our model produces observations that accurately and precisely reproduce the cluster morphology, which is a critical ingredient for determining a cluster's dynamical state and core type. Our model will advance our understanding of galaxy clusters by improving follow-up selection, and it demonstrates that image-to-image deep learning algorithms are a viable method for simulating realistic follow-up observations.

Keywords: convolutional neural networks; neural networks; galaxy clusters; observational cosmology; astronomical methods; x-ray astronomy; x-ray surveys; astronomy image processing; astronomy data analysis
Toward Horizon-scale Accretion onto Supermassive Black Holes in Elliptical Galaxies

We present high-resolution, three-dimensional hydrodynamic simulations of the fueling of supermassive black holes in elliptical galaxies from a turbulent medium on galactic scales, taking M87* as a typical case. The simulations use a new GPU-accelerated version of the Athena++ AMR code, and they span more than six orders of magnitude in radius, reaching scales similar to that of the black hole horizon. The key physical ingredients are radiative cooling and a phenomenological heating model. We find that the accretion flow takes the form of multiphase gas at radii less than about a kpc. The cold gas accretion includes two dynamically distinct stages: the typical disk stage in which the cold gas resides in a rotationally supported disk, and relatively rare chaotic stages (≲10% of the time) in which the cold gas inflows via chaotic streams. Though cold gas accretion dominates the time-averaged accretion rate at intermediate radii, accretion at the smallest radii is dominated by hot virialized gas at most times. The accretion rate scales with radius as $\dot{M}\propto {r}^{1/2}$ when hot gas dominates, and we obtain $\dot{M}\simeq {10}^{-4}\mbox{--}{10}^{-3}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ near the event horizon, similar to what is inferred from EHT observations. The orientation of the cold gas disk can differ significantly on different spatial scales. We propose a subgrid model for accretion in lower-resolution simulations in which the hot gas accretion rate is suppressed relative to the Bondi rate by $\sim {({r}_{{\rm{g}}}/{r}_{\mathrm{Bondi}})}^{1/2}$ . Our results can also provide more realistic initial conditions for simulations of black hole accretion at the event horizon scale.

Keywords: accretion; supermassive black holes; active galactic nuclei; elliptical galaxies
Probing Uncertainties in Diagnostics of a Synthetic Chromosphere

Effective spectroscopic diagnostics rely on the ability to convert a particular flux measurement into a physical interpretation. Knowledge of uncertainty is a central component of diagnostics. We present data from a simulated solar-like chromosphere, where we have addressed the question of whether degeneracy is a problem in mapping from a non-LTE chromospheric line profile to a particular vertical stratification of atmospheric properties along the line of sight. Our results indicate that stratification degeneracies do exist, at least in our simulated atmosphere. We quantify this effect through the creation of posterior densities for atmospheric properties based on the Mg II h line profile using the approximate Bayesian computation (ABC) technique. We find that the predictive power of the ABC temperature posterior systematically varies as a function of atmospheric column mass and ground-truth temperature. The ABC posteriors more effectively reproduce the spectral intensity in the Ca II 8542 Å line than they do temperature stratification, although residual error in the Ca II line core is common. Our results illustrate that some degeneracies should be alleviated through simultaneous analysis of multiple chromospheric lines.

Keywords: solar chromosphere; spectroscopy
Proton Synchrotron Gamma-Rays and the Energy Crisis in Blazars

The origin of high-energy emission in blazars jets (I.e., leptonic versus hadronic) has been a longstanding matter of debate. Here, we focus on one variant of hadronic models where proton synchrotron radiation accounts for the observed steady γ-ray blazar emission. Using analytical methods, we derive the minimum jet power ( ${P}_{j,\min }$ ) for the largest blazar sample analyzed to date (145 sources), taking into account uncertainties of observables and jet's physical parameters. We compare ${P}_{j,\min }$ against three characteristic energy estimators for accreting systems, I.e., the Eddington luminosity, the accretion disk luminosity, and the power of the Blandford-Znajek process, and find that ${P}_{j,\min }$ is about 2 orders of magnitude higher than all energetic estimators for the majority of our sample. The derived magnetic field strengths in the emission region require either large amplification of the jet's magnetic field (factor of 30) or place the γ-ray production site at sub-pc scales. The expected neutrino emission peaks at ∼0.1-10 EeV, with typical peak neutrino fluxes ∼10-4 times lower than the peak γ-ray fluxes. We conclude that if relativistic hadrons are present in blazar jets, they can only produce a radiatively subdominant component of the overall spectral energy distribution of the blazar's steady emission.

Keywords: blazars; relativistic jets; radiative processes; non-thermal radiation sources; neutrino astronomy; supermassive black holes; black hole physics
Does Matter Matter? Using the Mass Distribution to Distinguish Neutron Stars and Black Holes

Gravitational-wave detectors have opened a new window through which we can observe black holes (BHs) and neutron stars (NSs). Analyzing the 11 detections from LIGO/Virgo's first gravitational-wave catalog, GWTC-1, we investigate whether the power-law fit to the BH mass spectrum can also accommodate the binary neutron star (BNS) event GW170817, or whether we require an additional feature, such as a mass gap in between the NS and BH populations. We find that with respect to the power-law fit to binary black hole (BBH) masses, GW170817 is an outlier at the 0.13% level, suggesting a distinction between NS and BH masses. A single power-law fit across the entire mass range is in mild tension with (a) the detection of one source in the BNS mass range (∼1-2.5 M⊙), (b) the absence of detections in the "mass-gap" range (∼2.5-5 M⊙), and (c) the detection of 10 sources in the BBH mass range (≳5 M⊙). Instead, the data favor models with a feature between NS and BH masses, including a mass gap (Bayes factor of 4.6) and a break in the power law, with a steeper slope at NS masses compared to BH masses (91% credibility). We estimate the merger rates of compact binaries based on our fit to the global mass distribution, finding ${{R}}_{{\rm{B}}{\rm{N}}{\rm{S}}}={871}_{-805}^{+3015}$ and ${{ \mathcal R }}_{\mathrm{BBH}}={47.5}_{-28.8}^{+57.9}\ {\mathrm{Gpc}}^{-3}\ {\mathrm{yr}}^{-1}$ . We conclude that, even in the absence of any prior knowledge of the difference between NSs and BHs, the gravitational-wave data alone already suggest two distinct populations of compact objects.

Keywords: astrophysical black holes; compact objects; stellar mass black holes; neutron stars; gravitational wave astronomy; gravitational waves; astrostatistics
On the Abundances of Lanthanides in HgMn Stars

Little is known about the abundances of lanthanides in the Chemically Peculiar HgMn stars. Evidence is presented in this Note that they are not important absorbers in the classical HgMn stars μ Lep and β Scl. A fully consistent abundance analysis of lanthanides on a single temperature scale, using the same atomic data and including hyperfine structure for a larger number of HgMn stars is necessary.

Keywords: chemically peculiar stars; mercury-manganese stars
Choked Precessing Jets in Tidal Disruption Events and High-energy Neutrinos

It has been suggested that relativistic jets might have been commonly formed in tidal disruption events (TDEs), but those with relatively weak power could be choked by the surrounding envelope. The discovery of high-energy neutrinos possibly associated with some normal TDEs may support this picture in the hypothesis that the neutrinos are produced by choked jets. Recently, it was noted that disrupted stars generally have misaligned orbits with respect to the supermassive black hole spin axis, and highly misaligned precessing jets are more likely to be choked. Here we revisit the jet breakout condition for misaligned precessing jets by considering that the jet could be collimated by the cocoon pressure while propagating in the disk wind envelope. The jet head opening angle decreases as the jet propagates in the envelope, but the minimum power of a successful jet remains unchanged in terms of the physical jet power. We further calculate the neutrino flux from choked precessing jets, assuming that the cocoon energy does not exceed the kinetic energy of the disk wind. We find that neutrino flux from highly misaligned choked jets is sufficient to explain the neutrinos from AT2019aalc, while it is marginal to explain the neutrinos from AT2019dsg and AT2019fdr. The latter could be produced by weakly misaligned choked jets, since the duty cycle that the jet sweeps across increases as the misaligned angle decreases. We also show that the population of choked TDE jets could contribute to ∼10% of the observed diffuse neutrino flux measured by IceCube.

Keywords: neutrino astronomy; tidal disruption; relativistic jets
A New Planet Candidate Detected in a Dust Gap of the Disk around HD 163296 through Localized Kinematic Signatures: An Observational Validation of the DISCMINER

We report the robust detection of coherent, localized deviations from Keplerian rotation possibly associated with the presence of two giant planets embedded in the disk around HD 163296. The analysis is performed using the DISCMINER channel map modeling framework on 12CO J = 2-1 DSHARP data. Not only orbital radius but also azimuth of the planets are retrieved by our technique. One of the candidate planets, detected at R = 94 ± 6 au, ϕ = 50° ± 3° (P94), is near the center of one of the gaps in dust continuum emission and is consistent with a planet mass of 1 M Jup. The other planet, located at R = 261 ± 4 au, ϕ = 57° ± 1° (P261), is in the region where a velocity kink was previously observed in 12CO channel maps. Also, we provide a simultaneous description of the height and temperature of the upper and lower emitting surfaces of the disk and propose the line width as a solid observable to track gas substructure. Using azimuthally averaged line width profiles, we detect gas gaps at R = 38, 88, and 136 au, closely matching the location of their dust and kinematical counterparts. Furthermore, we observe strong azimuthal asymmetries in line widths around the gas gap at R = 88 au, possibly linked to turbulent motions driven by the P94 planet. Our results confirm that the DISCMINER is capable of finding localized, otherwise unseen velocity perturbations thanks to its robust statistical framework, but also that it is well suited for studies of the gas properties and vertical structure of protoplanetary disks.

Keywords: protoplanetary disks; planetary-disk interactions; exoplanet detection methods
Investigating the Multiband Nonthermal Radiative Properties of HESS J1420-607

HESS J1420-607 is a γ-ray emitting source associated with the pulsar wind nebula (PWN) powered by the energetic pulsar PSR J1420-6048. Based on 14 yr of data obtained with the Fermi Large Area Telescope, we re-analyzed its GeV γ-ray radiative properties, resulting in detailed spectra obtained within the band 10-200 GeV. Moreover, we use a one-zone time-dependent model for the multiband nonthermal emission from pulsar wind nebulae to investigate the radiative properties of the nebula associated with HESS J1420-607. Assuming that the electrons/positrons are injected into the PWN with a broken power law spectrum with indexes of ~1.6 and ~2.7, as well as a break Lorentz factor of ~5 × 106, the results indicate that the multi-wavelength spectral energy distribution is consistent with the detected fluxes in both X-rays and γ-rays. The results support that the γ-rays detected can be produced via inverse Compton scattering of the energetic electrons/positrons within the PWN.

Keywords: pulsar wind nebulae; nebulae; supernova remnants; gamma-ray sources
Hidden Companions to Intermediate-mass Stars. VII. Discovery of a 0.76 M ⊙, 39 au Companion to the Ap Star HIP 88866 = π Pavonis

HIP 88866 = π Pavonis is a nearby chemically peculiar Ap star. Here we report the discovery of a companion with an H band contrast ΔH = 3.63 at a projected separation ρ = 959 mas ↔ 39 au based on the acquisition camera image of a VLTI/GRAVITY observation. Isochrone fitting yields masses M A = 1.80 M ⊙ and M B = 0.76 M ⊙ and an age of 1.4 Gyr. However, even for a face-on orbit the companion cannot fully account for the GaiaDR3-Hipparcos proper motion change of π Pav. We present constraints on the nature and location of a putative additional closer companion based on the lack of its detection in the interferometric data. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Keywords: multiple stars; ap stars; optical interferometry
Detection of δ Scuti Pulsators in the Eclipsing Binaries Observed by TESS

Based on 2 minute cadence TESS data from sectors 1-50, we report the results of the systematic extraction of δ Scuti-type pulsations in the 6431 eclipsing binaries with orbital periods shorter than 13 days. A total number of 242 pulsators were found in those systems, including 143 new discoveries. We examined their pulsation properties based on the H-R diagram and the relationships between the dominant pulsation period P dom, orbital period P orb, and effective temperature T eff. As a consequence, 216 targets are likely δ Scuti stars (123 new), 11 likely γ Doradus-δ Scuti hybrid stars (8 new), 5 likely β Cephei stars (4 new), 4 likely δ Scuti-γ Doradus hybrid stars (3 new), 3 likely Maia stars (3 new), 2 likely pulsating red giants (1 new), and a new unclassified star. As for the six new δ Scuti pulsators in eclipsing binaries with P orb < 0.65 days, we found that three of them significantly exceed the upper limits of the P dom/P orb ratio. This may indicate that P dom and P orb are uncorrelated for them. Finally, we statistically analyzed the dominant pulsation periods of the 216 δ Scuti stars in eclipsing binaries. Those stars concentrate around 225 μHz and the proportion of stars in the high-frequency region is significantly higher than that of single stars, which could be ascribed to the mass-transfer process.

Keywords: asteroseismology; pulsating variable stars; delta scuti variable stars; stellar oscillations
MSWIM2D: Two-dimensional Outer Heliosphere Solar Wind Modeling

The vast size of the Sun's heliosphere, combined with sparse spacecraft measurements over that large domain, makes numerical modeling a critical tool to predict solar wind conditions where there are no measurements. This study models the solar wind propagation in 2D using the BATSRUS MHD solver to form the MSWIM2D data set of solar wind in the outer heliosphere. Representing the solar wind from 1 to 75 au in the ecliptic plane, a continuous model run from 1995-present has been performed. The results are available for free at http://csem.engin.umich.edu/mswim2d/. The web interface extracts output at desired locations and times. In addition to solar wind ions, the model includes neutrals coming from the interstellar medium to reproduce the slowing of the solar wind in the outer heliosphere and to extend the utility of the model to larger radial distances. The inclusion of neutral hydrogen is critical to recreating the solar wind accurately outside of ~4 au. The inner boundary is filled by interpolating and time-shifting in situ observations from L1 and STEREO spacecraft when available. Using multiple spacecraft provides a more accurate boundary condition than a single spacecraft with time shifting alone. Validations of MSWIM2D are performed using MAVEN and New Horizons observations. The results demonstrate the efficacy of this model to propagate the solar wind to large distances and obtain practical, useful solar wind predictions. For example, the rms error of solar wind speed prediction at Mars is only 66 km s-1 and at Pluto is a mere 25 km s-1.

Keywords: solar wind; heliosphere; magnetohydrodynamics; pluto; mars
Discovering New Strong Gravitational Lenses in the DESI Legacy Imaging Surveys

We have conducted a search for new strong gravitational lensing systems in the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys' Data Release 8. We use deep residual neural networks, building on previous work presented by Huang et al. These surveys together cover approximately one-third of the sky visible from the Northern Hemisphere, reaching a z-band AB magnitude of ∼22.5. We compile a training sample that consists of known lensing systems as well as non-lenses in the Legacy Surveys and the Dark Energy Survey. After applying our trained neural networks to the survey data, we visually inspect and rank images with probabilities above a threshold. Here we present 1210 new strong lens candidates.

Keywords: strong gravitational lensing; high-redshift galaxies; agn host galaxies; galaxies; galaxy clusters; galaxy groups; quasars