adsabs/SciX_UAT_keywords huggingface dataset:
Dynamical Interactions and Mass Loss within the Uranian System

The origin and evolution of planetary rings and moons remains an active area of study, particularly as they relate to the impact history and volatile inventory of the outer solar system. The Uranian system contains a complex system of rings that are coplanar with the highly inclined planetary equator relative to the orbital plane. Uranus also harbors five primary regular moons that play an important role in the distribution of material that surrounds the planet. Here we present the results of a dynamical simulation suite for the Uranian system, intended to explore the interaction between the five primary regular moons and particles within the system. We identify regions of extreme mass loss within 40 planetary radii of Uranus, including eccentricity excitation of particle orbits at resonance locations that can promote moonlet formation within the rings. We calculate a total dynamical particle mass-loss rate of 35% within 0.5 × 106 yr and 40% mass loss within 107 yr. We discuss the implications for postimpact material, including dynamical truncation of stable ring locations and/or locations of moon formation promoted by dynamical excitation of ring material.

Keywords: uranus; uranian satellites; orbital evolution; orbital resonances; orbits; dynamical evolution; planetary rings; solar system; solar system planets
Implications of an Extended Dark Energy Model with Massive Neutrinos

Recently there have been reports of finding a lower bound on the neutrino mass parameter (Σm ν ) when using the Atacama Cosmology Telescope (ACT) and SPTpol data; however, these bounds on the Σm ν are still weaker for most cases around the 1σ level. In this context, here in this work, we study the consequences of using an enlarged four parameter dynamical dark energy equation of state on the neutrino mass parameter as well as on the Hubble and S8 tensions. The four parameter dark energy equation of state incorporates a generic nonlinear monotonic evolution of the dark energy equation of state, where the four parameters are the early and the present value of the equation of state, the transition scale factor, and the sharpness of the transition. We report that with lensing-marginalized Planck + BAO + Pantheon and prior on absolute magnitude M B , and KIDS/Viking S 8 prior, the model favors a nonzero value for the neutrino mass parameter at most at the 1σ level ( ${\rm{\Sigma }}{m}_{\nu }={0.1847}_{-0.165}^{+0.0698}$ eV). In this case this model also brings down the Hubble tension to a 2.5σ level and the S8 tension to a ~1.5σ level. This model also provides tighter constraints on the value of the dark energy equation of state at present epoch w 0 ( ${w}_{0}=-{0.9901}_{-0.0766}^{+0.0561}$ ) in comparison to the Chevalier-Polarski and Linder-like parameterization.

Keywords: dark energy
Cold Gas in Massive Galaxies as a Critical Test of Black Hole Feedback Models

Black hole feedback has been widely implemented as the key recipe to quench star formation in massive galaxies in modern semianalytic models and hydrodynamical simulations. As the theoretical details surrounding the accretion and feedback of black holes continue to be refined, various feedback models have been implemented across simulations, with notable differences in their outcomes. Yet, most of these simulations have successfully reproduced some observations, such as the stellar mass function and star formation rate density in the local universe. We use the recent observation of the change in the neutral hydrogen gas mass (including both H2 and H I) with the star formation rate of massive central disk galaxies as a critical constraint of black hole feedback models across several simulations. We find that the predictions of IllustrisTNG agree with the observations much better than the other models tested in this work. This favors IllustrisTNG's treatment of active galactic nuclei (AGN)-where kinetic winds are driven by black holes at low accretion rates-as more plausible among those we test. In turn, this also indirectly supports the idea that the massive central disk galaxy population in the local universe was likely quenched by AGN feedback.

Keywords: galaxies
Amplification of Turbulence in Contracting Prestellar Cores in Primordial Minihalos

We investigate the amplification of turbulence through gravitational contraction of the primordial gas in minihalos. We perform numerical simulations to follow the cloud collapse, assuming polytropic equations of state for different initial turbulent Mach numbers and resolutions. We find that the turbulent velocity is amplified solely by gravitational contraction, and eventually becomes comparable to the sound speed, even for small initial turbulent Mach numbers ( ${{ \mathcal M }}_{0}\gtrsim 0.05$ ). We derive an analytic formula for the amplification of turbulent velocity in a collapsing cloud, and find that our numerical results are consistent with the formula. These results suggest that the turbulence can play an important role in collapsing clouds for general cases.

Keywords: population iii stars; early universe; hydrodynamics; collapsing clouds
Magnetic Field Strength Effects on Nucleosynthesis from Neutron Star Merger Outflows

Magnetohydrodynamic turbulence drives the central engine of post-merger remnants, potentially powering both a nucleosynthetically active disk wind and the relativistic jet behind a short gamma-ray burst. We explore the impact of the magnetic field on this engine by simulating three post-merger black hole accretion disks using general relativistic magnetohydrodynamics with Monte Carlo neutrino transport, in each case varying the initial magnetic field strength. We find increasing ejecta masses associated with increasing magnetic field strength. We find that a fairly robust main r-process pattern is produced in all three cases, scaled by the ejected mass. Changing the initial magnetic field strength has a considerable effect on the geometry of the outflow and hints at complex central engine dynamics influencing lanthanide outflows. We find that actinide production is especially sensitive to magnetic field strength, with the overall actinide mass fraction calculated at 1 Gyr post-merger increasing by more than a factor of 6 with a tenfold increase in magnetic field strength. This hints at a possible connection to the variability in actinide enhancements exhibited by metal-poor, r-process-enhanced stars.

Keywords: r-process; nuclear astrophysics; accretion; magnetohydrodynamical simulations; magnetohydrodynamics; magnetic fields; neutron stars; nucleosynthesis
Toward Solving the Puzzle: Dissecting the Complex Merger A521 with Multiwavelength Data

A521 has been a subject of extensive panchromatic studies from X-ray to radio. The cluster possesses a number of remarkable features, including a bright radio relic with a steep spectrum, more than three distinct galaxy groups forming a filament, and two disturbed X-ray peaks at odds with the distant position and tilted orientation of the radio relic. These lines of evidence indicate a complex merger. In this paper, we present a multiwavelength study of A521 based on Subaru optical, Hubble Space Telescope infrared, Chandra X-ray, Giant Metrewave Radio Telescope radio, and Multiple Mirror Telescope optical spectroscopic observations. Our weak-lensing (WL) analysis with improved systematics control reveals that A521 is mainly composed of three substructures aligned in the northwest to southeast orientation. These WL mass substructures are remarkably well-aligned with the cluster optical luminosity distribution constructed from our new enhanced cluster member catalog. These individual substructure masses are determined by simultaneously fitting three Navarro-Frenk-White profiles. We find that the total mass of A521 modeled by the superposition of the three halos is ${13.0}_{-1.3}^{+1.0}\times {10}^{14}{M}_{\odot }$ , a factor of 2 higher than the previous WL measurement. With these WL mass constraints combined with X-ray and radio features, we consider two merging scenarios, carry out the corresponding numerical simulations, and discuss the strengths and weaknesses of each case.

Keywords: galaxy clusters; abell clusters; intracluster medium; gravitational lensing
Atmospheric Erosion by Giant Impacts onto Terrestrial Planets

We examine the mechanisms by which the atmosphere can be eroded by giant impacts onto Earth-like planets with thin atmospheres, using 3D smoothed particle hydrodynamics simulations with sufficient resolution to directly model the fate of low-mass atmospheres. We present a simple scaling law to estimate the fraction lost for any impact angle and speed in this regime. In the canonical Moon-forming impact, only around 10% of the atmosphere would have been lost from the immediate effects of the collision. There is a gradual transition from removing almost none to almost all of the atmosphere for a grazing impact as it becomes more head-on or increases in speed, including complex, nonmonotonic behavior at low impact angles. In contrast, for head-on impacts, a slightly greater speed can suddenly remove much more atmosphere. Our results broadly agree with the application of 1D models of local atmosphere loss to the ground speeds measured directly from our simulations. However, previous analytical models of shock-wave propagation from an idealized point-mass impact significantly underestimate the ground speeds and hence the total erosion. The strong dependence on impact angle and the interplay of multiple nonlinear and asymmetrical loss mechanisms highlight the need for 3D simulations in order to make realistic predictions.

Keywords: hydrodynamical simulations; earth atmosphere; planetary atmospheres; impact phenomena
Spatially Quasi-periodic Finger-like Auroras during Substorms

North-south-aligned discrete auroras are common phenomena during substorms. A quasi-periodic form of such auroras distributed azimuthally in the nightside resembles a finger-like morphology. They were noticed in sawtooth-time substorms, but have not yet been paid much attention during other geomagnetic times. In this study, we investigate the longitudinal periodicity of those auroras for different types of substorms using IMAGE data from 2001 to 2003. Using an automated detection algorithm, we identified multiple north-south-aligned thin auroral structures in auroral images and found that their average center and length in latitude, and longitudinal wavelength (∼25°) are essentially the same. However, the occurrent rates for finger-like auroras are substantially different, 83%, 64%, and 18% for sawtooth-time substorms, storm-time substorms and isolated substorms, respectively. Therefore, statistical results indicate that finger-like auroras occur in favor of geomagnetically more active times. Combining our data analysis and previous simulations, we suggest that interchange instability is a possible mechanism of spatially quasi-periodic finger-like auroras when a substorm injection happens in a very wide local time. It is particularly important to point out that the sawtooth events not only have a temporal periodicity as defined in particle injections, but also have a spatial periodicity as observed in auroral morphology for the majority of them.

Keywords: magnetic fields; space plasmas; magnetohydrodynamics
NuSTAR Observation of Energy Release in 11 Solar Microflares

Solar flares are explosive releases of magnetic energy. Hard X-ray (HXR) flare emission originates from both hot (millions of Kelvin) plasma and nonthermal accelerated particles, giving insight into flare energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR) utilizes direct-focusing optics to attain much higher sensitivity in the HXR range than that of previous indirect imagers. This paper presents 11 NuSTAR microflares from two active regions (AR 12671 on 2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and energetic properties of each are discussed in context with previously published HXR brightenings. They are seen to display several "large flare" properties, such as impulsive time profiles and earlier peak times in higher-energy HXRs. For two events where the active region background could be removed, microflare emission did not display spatial complexity; differing NuSTAR energy ranges had equivalent emission centroids. Finally, spectral fitting showed a high-energy excess over a single thermal model in all events. This excess was consistent with additional higher-temperature plasma volumes in 10/11 microflares and only with an accelerated particle distribution in the last. Previous NuSTAR studies focused on one or a few microflares at a time, making this the first to collectively examine a sizable number of events. Additionally, this paper introduces an observed variation in the NuSTAR gain unique to the extremely low livetime (<1%) regime and establishes a correction method to be used in future NuSTAR solar spectral analysis.

Keywords: the sun; solar flare spectra; solar x-ray flares; non-thermal radiation sources; solar flares; solar physics
Galaxy Morphology Network: A Convolutional Neural Network Used to Study Morphology and Quenching in ∼100,000 SDSS and ∼20,000 CANDELS Galaxies

We examine morphology-separated color-mass diagrams to study the quenching of star formation in ∼100,000 (z ∼ 0) Sloan Digital Sky Survey (SDSS) and ∼20,000 (z ∼ 1) Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) galaxies. To classify galaxies morphologically, we developed Galaxy Morphology Network (GAMORNET), a convolutional neural network that classifies galaxies according to their bulge-to-total light ratio. GAMORNET does not need a large training set of real data and can be applied to data sets with a range of signal-to-noise ratios and spatial resolutions. GAMORNET's source code as well as the trained models are made public as part of this work. We first trained GAMORNET on simulations of galaxies with a bulge and a disk component and then transfer learned using ∼25% of each data set to achieve misclassification rates of ≲5%. The misclassified sample of galaxies is dominated by small galaxies with low signal-to-noise ratios. Using the GAMORNET classifications, we find that bulge- and disk-dominated galaxies have distinct color-mass diagrams, in agreement with previous studies. For both SDSS and CANDELS galaxies, disk-dominated galaxies peak in the blue cloud, across a broad range of masses, consistent with the slow exhaustion of star-forming gas with no rapid quenching. A small population of red disks is found at high mass (∼14% of disks at z ∼ 0 and 2% of disks at z ∼ 1). In contrast, bulge-dominated galaxies are mostly red, with much smaller numbers down toward the blue cloud, suggesting rapid quenching and fast evolution across the green valley. This inferred difference in quenching mechanism is in agreement with previous studies that used other morphology classification techniques on much smaller samples at z ∼ 0 and z ∼ 1.

Keywords: galaxies; galaxy classification systems; galaxy evolution; galaxy quenching; astronomy data analysis; convolutional neural networks; neural networks
H I in Molecular Clouds: Irradiation by FUV Plus Cosmic Rays

We extend the analytic theory presented by Sternberg et al. and Bialy & Sternberg for the production of atomic hydrogen (H I) via far-ultraviolet (FUV) photodissociation at the boundaries of dense interstellar molecular (H2) clouds to also include the effects of penetrating (low-energy) cosmic rays (CRs) for the growth of the total H I column densities. We compute the steady-state abundances of the H I and H2 in one-dimensional gas slabs in which the FUV photodissociation rates are reduced by depth-dependent H2 self-shielding and dust absorption and the CR ionization rates are either constant or reduced by transport effects. The solutions for the H I and H2 density profiles and the integrated H I columns depend primarily on the ratios I UV/Rn and ζ/Rn, where I UV is the intensity of the photodissociating FUV field, ζ is the H2 CR ionization rate, n is the hydrogen gas density, and R is the dust surface H2 formation rate coefficient. We present computations for a wide range of FUV field strengths, CR ionization rates, and dust-to-gas ratios. We develop analytic expressions for the growth of the H I column densities. For Galactic giant molecular clouds (GMCs) with multiphased (warm/cold) H I envelopes, the interior CR zones will dominate the production of the H I only if $\zeta \gtrsim 4.5\times {10}^{-16}\times {({M}_{\mathrm{GMC}}/{10}^{6}\ {M}_{\odot })}^{-1/2}$ s-1, where M GMC is the GMC mass, and including attenuation of the CR fluxes. For most Galactic GMCs and conditions, FUV photodissociation dominates over CR ionization for the production of the H I column densities. Furthermore, the CRs do not affect the H I-to-H2 transition points.

Keywords: interstellar atomic gas; molecular clouds; galactic cosmic rays; interstellar dust extinction; radiative transfer; neutral hydrogen clouds; giant molecular clouds
Depth-to-diameter Ratios of Fresh Craters on the Moon and Implications for Surface Age Estimates

The depth-to-diameter (d/D) ratios of small lunar craters (D < 400 m) can be used to determine important properties of the upper regolith, specifically material strength or thickness. The d/D is also an important component of topographic diffusion models that describe how different erosive processes influence and change the topography of a surface over time, and these models have been applied to estimate surface ages. These models must make assumptions regarding rates of erosion and the initial d/D of a crater. Previous works investigating d/D of small craters, which use various methodologies to calculate depth, typically assume that a fresh appearing crater is a young crater. Work presented here provides d/D measurements of known—rather than assumed—young, meter-scale craters to provide better constraints on small crater depths and to help further our understanding of lunar surface ages and upper regolith properties. Given the interest in impact crater modification at small, human scales on the Moon and the wide range of assumptions built into topographic diffusion models and their predictions, understanding whether the results for initial d/D from past work hold up under different analyses is critical. We observed no distinct trends in d/D for small, young craters and report a wide range of d/D from 0.08 to 0.215, in contrast with past work that derived different averages based on crater size. The variation in d/D may correspond to heterogeneous regolith properties or be a result of a data source artifact.

Keywords: lunar craters; the moon
Simulating the Eclipsing Binary Yields of the Rubin Observatory in the Galactic Field and Star Clusters

We present a study of the detection and recovery efficiency of the Rubin Observatory for detached eclipsing binaries (EBs) in the galactic field, globular clusters (GCs), and open clusters (OCs), with a focus on comparing two proposed observing strategies: a standard cadence (baseline) and a cadence that samples the galactic plane more evenly (colossus). We generate realistic input binary populations in all observing fields of the Rubin Observatory, simulate the expected observations in each filter, and attempt to characterize the EBs using these simulated observations. In our models, we predict that the baseline cadence will enable the Rubin Observatory to observe about three million EBs; our technique could recover and characterize nearly one million of these in the field and thousands within star clusters. If the colossus cadence is used, the number of recovered EBs would increase by an overall factor of about 1.7 in the field and in globular clusters, and a factor of about 3 in open clusters. Including semidetached and contact systems could increase the number of recovered EBs by an additional factor of about 2.5 to 3. Regardless of the cadence, observations from the Rubin Observatory could reveal statistically significant physical distinctions between the distributions of EB orbital elements between the field, GCs, and OCs. Simulations such as these can be used to bias correct the sample of Rubin Observatory EBs to study the intrinsic properties of the full binary populations in the field and star clusters.

Keywords: open star clusters; globular star clusters; eclipsing binary stars; time series analysis; stellar photometry; astronomy data modeling; stellar populations; stellar astronomy
Compact Bright Radio-loud AGNs. III. A Large VLBA Survey at 43 GHz

We present the results from the 43 GHz Very Long Baseline Array (VLBA) observations of 124 compact radio-loud active galactic nuclei (AGNs) that were conducted between 2014 November and 2016 May. The typical dimensions of the restoring beam in each image are about 0.5 mas × 0.2 mas. The highest resolution of 0.2 mas corresponds to a physical size of 0.02 pc for the lowest redshift source in the sample. The 43 GHz very long baseline interferometry (VLBI) images of 97 AGNs are presented for the first time. We study the source compactness on milliarcsecond and submilliarcsecond scales, and suggest that 95 sources in our sample are suitable for future space VLBI observations. By analyzing our data supplemented with other VLBA AGN surveys from the literature, we find that the core brightness temperature increases with increasing frequency below a break frequency ∼7 GHz, and decreases between ∼7 and 240 GHz but increases again above 240 GHz in the rest frame of the sources. This indicates that the synchrotron opacity changes from optically thick to thin. We also find a strong statistical correlation between radio and γ-ray flux densities. Our correlation is tighter than those in the literature derived from lower-frequency VLBI data, suggesting that the γ-ray emission is produced more cospatially with the 43 GHz VLBA core emission. This correlation can also be extrapolated to the unbeamed AGN population, implying that a universal γ-ray production mechanism might be at work for all types of AGNs.

Keywords: very long baseline interferometry; active galaxies; surveys; radio loud quasars; jets
Optical- and UV-continuum Morphologies of Compact Radio Source Hosts

We present the first systematic search for UV signatures from radio source-driven active galactic nuclei (AGN) feedback in Compact Steep Spectrum (CSS) radio galaxies. Owing to their characteristic sub-galactic jets (1–20 kpc projected linear sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback via jet-triggered star formation. The sample consists of seven powerful CSS galaxies, and two galaxies host to radio sources >20 kpc as the control, at low to intermediate redshifts (z < 0.6). Our new Hubble Space Telescope images show extended UV continuum emission in six out of seven CSS galaxies, with five CSS hosts exhibiting UV knots cospatial and aligned along the radio-jet axis. Young (≲ 10 Myr), massive (≳ 5 M ⊙) stellar populations are likely to be the dominant source of the blue excess emission in radio galaxies at these redshifts. Hence, the radio-aligned UV regions could be attributed to jet-induced starbursts. Lower near-UV star formation rates compared to other indicators suggest low scattered AGN light contribution to the observed UV. Dust attenuation of UV emission appears unlikely from high internal extinction correction estimates in most sources. Comparison with evolutionary synthesis models shows that our observations are consistent with recent (∼1‑8 Myr old) star-forming activity likely triggered by current or an earlier episode of radio emission, or by a confined radio source that has frustrated growth, due to a dense environment. While follow-up spectroscopic and polarized light observations are needed to constrain the activity-related components in the observed UV, the detection of jet-induced star formation is a confirmation of an important prediction of the jet feedback paradigm.

Keywords: agn host galaxies; radio galaxies; active galactic nuclei; radio active galactic nuclei; radio jets