adsabs/SciX_UAT_keywords huggingface dataset:
The Gas Accretion History of Low-mass Halos within the Cosmic Web from Cosmological Simulations

Using high-resolution hydrodynamical cosmological simulations, we study the gas accretion history of low-mass halos located in a field-like, low-density environment. We track their evolution individually from the early, pre-reionization era, through reionization, and beyond until z = 0. Before reionization, low-mass halos accrete cool cosmic-web gas at a very rapid rate, often reaching the highest gas mass they will ever have. But when reionization occurs, we see that almost all halos lose significant quantities of their gas content, although some respond less quickly than others. We find that the response rate is influenced by halo mass first, and secondarily by their internal gas density at the epoch of reionization. Reionization also fully ionizes the cosmic-web gas by z ∼ 6. As a result, the lowest mass halos (M ∼ 106 h-1 M⊙ at z = 6) can never again re-accrete gas from the cosmic web, and by z ∼ 5 have lost all their internal gas to ionization, resulting in a halt in star formation at this epoch. However, more massive halos can recover from their gas mass loss, and re-accrete ionized cosmic-web gas. We find the efficiency of this re-accretion is a function of halo mass first, followed by local surrounding gas density. Halos that are closer to the cosmic-web structure can accrete denser gas more rapidly. We find that our lower mass halos have a sweet spot for rapid, dense gas accretion at distances of roughly 1-5 virial radii from the most massive halos in our sample (>108 h-1 M⊙), as these tend to be embedded deeply within the cosmic web.

Keywords: galaxy formation; dwarf galaxies; galaxy evolution
Modeling Stellar Ca II H and K Emission Variations. I. Effect of Inclination on the S-index

The emission in the near-ultraviolet Ca II H and K lines is modulated by stellar magnetic activity. Although this emission, quantified via the S-index, has been serving as a prime proxy of stellar magnetic activity for several decades, many aspects of the complex relation between stellar magnetism and Ca II H and K emission are still unclear. The amount of measured Ca II H and K emission is suspected to be affected not only by the stellar intrinsic properties but also by the inclination angle of the stellar rotation axis. Until now, such an inclination effect on the S-index has remained largely unexplored. To fill this gap, we develop a physics-based model to calculate S-index, focusing on the Sun. Using the distributions of solar magnetic features derived from observations together with Ca II H and K spectra synthesized in non-local thermodynamic equilibrium, we validate our model by successfully reconstructing the observed variations of the solar S-index over four activity cycles. Further, using the distribution of magnetic features over the visible solar disk obtained from surface flux transport simulations, we obtain S-index time series dating back to 1700 and investigate the effect of inclination on S-index variability on both the magnetic activity cycle and the rotational timescales. We find that when going from an equatorial to a pole-on view, the amplitude of S-index variations decreases weakly on the activity cycle timescale and strongly on the rotational timescale (by about 22% and 81%, respectively, for a cycle of intermediate strength). The absolute value of the S-index depends only weakly on the inclination. We provide analytical expressions that model such dependencies.

Keywords: stellar activity; stellar chromospheres; solar faculae; plages; sunspots; radiative transfer
Neural Networks as Optimal Estimators to Marginalize Over Baryonic Effects

Many different studies have shown that a wealth of cosmological information resides on small, nonlinear scales. Unfortunately, there are two challenges to overcome to utilize that information. First, we do not know the optimal estimator that will allow us to retrieve the maximum information. Second, baryonic effects impact that regime significantly and in a poorly understood manner. Ideally, we would like to use an estimator that extracts the maximum cosmological information while marginalizing over baryonic effects. In this work we show that neural networks can achieve that when considering some simple scenarios. We made use of data where the maximum amount of cosmological information is known: power spectra and 2D Gaussian density fields. We also contaminate the data with simplified baryonic effects and train neural networks to predict the value of the cosmological parameters. For this data, we show that neural networks can (1) extract the maximum available cosmological information, (2) marginalize over baryonic effects, and (3) extract cosmological information that is buried in the regime dominated by baryonic physics. We also show that neural networks learn the priors of the data they are trained on, affecting their extrapolation properties. We conclude that a promising strategy to maximize the scientific return of cosmological experiments is to train neural networks on state-of-the-art numerical simulations with different strengths and implementations of baryonic effects.

Keywords: cosmology
Modeling Solids in Nuclear Astrophysics with Smoothed Particle Hydrodynamics

Smoothed particle hydrodynamics (SPH) is a frequently applied tool in computational astrophysics to solve the fluid dynamics equations governing the systems under study. For some problems, for example when involving asteroids and asteroid impacts, the additional inclusion of material strength is necessary in order to accurately describe the dynamics. In compact stars, that is white dwarfs and neutron stars, solid components are also present. Neutron stars have a solid crust, which is the strongest material known in nature. However, their dynamical evolution, when modeled via SPH or other computational fluid dynamics codes, is usually described as a purely fluid dynamics problem. Here, we present the first 3D simulations of neutron star crustal toroidal oscillations including material strength with the Los Alamos National Laboratory SPH code FleCSPH. In the first half of the paper, we present the numerical implementation of solid material modeling together with standard tests. The second half is on the simulation of crustal oscillations in the fundamental toroidal mode. Here, we dedicate a large fraction of the paper to approaches that can suppress numerical noise in the solid. If not minimized, the latter can dominate the crustal motion in the simulations.

Keywords: neutron stars; nuclear astrophysics; hydrodynamical simulations; astrophysical fluid dynamics; computational methods
Keck Infrared Transient Survey. I. Survey Description and Data Release 1

We present the Keck Infrared Transient Survey, a NASA Key Strategic Mission Support program to obtain near-infrared (NIR) spectra of astrophysical transients of all types, and its first data release, consisting of 105 NIR spectra of 50 transients. Such a data set is essential as we enter a new era of IR astronomy with the James Webb Space Telescope (JWST) and the upcoming Nancy Grace Roman Space Telescope (Roman). NIR spectral templates will be essential to search JWST images for stellar explosions of the first stars and to plan an effective Roman SN Ia cosmology survey, both key science objectives for mission success. Between 2022 February and 2023 July, we systematically obtained 274 NIR spectra of 146 astronomical transients, representing a significant increase in the number of available NIR spectra in the literature. Here, we describe the first release of data from the 2022A semester. We systematically observed three samples: a flux-limited sample that includes all transients <17 mag in a red optical band (usually ZTF r or ATLAS o bands); a volume-limited sample including all transients within redshift z < 0.01 (D ≈ 50 Mpc); and an SN Ia sample targeting objects at phases and light-curve parameters that had scant existing NIR data in the literature. The flux-limited sample is 39% complete (60% excluding SNe Ia), while the volume-limited sample is 54% complete and is 79% complete to z = 0.005. Transient classes observed include common Type Ia and core-collapse supernovae, tidal disruption events, luminous red novae, and the newly categorized hydrogen-free/helium-poor interacting Type Icn supernovae. We describe our observing procedures and data reduction using PypeIt, which requires minimal human interaction to ensure reproducibility.

Keywords: supernovae; transient sources; spectroscopy; infrared astronomy; surveys; type ia supernovae; tidal disruption
The Formation of Hard Very High Energy Spectra from Gamma-ray Burst Afterglows via Two-zone Synchrotron Self-Compton Emission

Electron Compton scattering of target photons into the gamma-ray energy band (inverse Compton scattering; IC) is commonly expected to dominate the very high energy (VHE) spectra in gamma-ray bursts (GRBs) especially during the afterglow phase. For sufficiently large center-of-mass energies in these collisions, the effect of the electron recoil starts reducing the scattering cross-section (the Klein-Nishina regime). The IC spectra generated in the Klein-Nishina regime is softer and has a smaller flux level compared to the synchrotron spectra produced by the same electrons. The detection of afterglow emission from nearby GRB190829A in the VHE domain with H.E.S.S. has revealed an unexpected feature: the slope of the VHE spectrum matches well the slope of the X-ray spectra, despite expectations that, for the IC production process, the impact of the Klein-Nishina effect should be strong. The multi-wavelength spectral energy distribution appears to be inconsistent with predictions of one-zone synchrotron-self-Compton models. We study the possible impact of two-zone configuration on the properties of IC emission when the magnetic field strength differs considerably between the two zones. Synchrotron photons from the strong magnetic field zone provide the dominant target for cooling of the electrons in the weak magnetic field zone, which results in a formation of hard electron distribution and consequently of a hard IC emission. We show that the two-zone model can provide a good description of the Swift's X-ray Telescope and VHE H.E.S.S. data.

Keywords: non-thermal radiation sources; gamma-ray transient sources; gamma-ray bursts; gamma-ray astronomy; particle astrophysics; high energy astrophysics; x-ray sources
Cosmicflows-4

With Cosmicflows-4, distances are compiled for 55,877 galaxies gathered into 38,065 groups. Eight methodologies are employed, with the largest numbers coming from the correlations between the photometric and kinematic properties of spiral galaxies (TF) and elliptical galaxies (FP). Supernovae that arise from degenerate progenitors (type Ia SNe) are an important overlapping component. Smaller contributions come from distance estimates from the surface brightness fluctuations of elliptical galaxies and the luminosities and expansion rates of core-collapse supernovae (SNe II). Cepheid period-luminosity relation and tip of the red giant branch observations founded on local stellar parallax measurements along with the geometric maser distance to NGC 4258 provide the absolute scaling of distances. The assembly of galaxies into groups is an important feature of the study in facilitating overlaps between methodologies. Merging between multiple contributions within a methodology and between methodologies is carried out with Bayesian Markov chain Monte Carlo procedures. The final assembly of distances is compatible with a value of the Hubble constant of H 0 = 74.6 km s-1 Mpc-1 with the small statistical error of ±0.8 km s-1 Mpc-1 but a large potential systematic error of ~3 km s-1 Mpc-1. Peculiar velocities can be inferred from the measured distances. The interpretation of the field of peculiar velocities is complex because of large errors on individual components and invites analyses beyond the scope of this study.

Keywords: distance indicators; galaxy distances; large-scale structure of the universe; observational cosmology; hubble constant
Tethys's Heat Fluxes Varied with Time in the Ithaca Chasma and Telemus Basin Region

We investigated how lithospheric heat fluxes varied temporally and spatially on the Saturnian moon Tethys, focusing on the region of Ithaca Chasma that overprints Telemus Impact Basin. Our results, derived from flexure associated with Ithaca, indicate elastic thicknesses of 4.1 ± 0.3 km to 6.4 ± 0.4 km and heat fluxes ranging from 12 to 39 mW m-2 assuming a nonporous pure H2O ice lithosphere. Our results for Ithaca's south limb are similar to previous estimates within the north limb, indicating consistent heat fluxes across a large spatial extent in this area. However, our estimates are lower than those for the older Telemus Basin (>60 mW m-2), revealing evidence that Tethys experienced a substantial temporal variation in heat fluxes in this region. Heat fluxes reflected by Ithaca are similar to previous estimates for Tethys's two youngest impact basins, Melanthius and Odysseus, suggesting that Ithaca may also be relatively young. If Tethys's lithosphere is porous, then our heat flux estimates for Ithaca Chasma drop to 12-38 mW m-2, 11-35 mW m-2, and 10-33 mW m-2 for 5%, 15%, and 25% porosities, respectively. If Tethys's lithosphere includes ~10% NH3-hydrates, then the estimates are 5-16 mW m-2, 5-15 mW m-2, 4-14 mW m-2, and 4-13 mW m-2 for 0%, 5%, 15%, and 25% porosities, respectively. Although we find that some ground-based reflectance spectra hint at 2.2 μm bands that may result from NH3-bearing species, the detected features are weak and may not result from surface constituents. Consequently, our heat flux estimates that assume a pure H2O ice lithosphere are likely more accurate.

Keywords: planetary science; saturnian satellites; thermal properties (ice); planetary thermal histories; ice spectroscopy
On the Determining Physical Factor of Jet-related Coronal Mass Ejections' Morphology in the High Corona

A solar jet can often cause coronal mass ejections (CMEs) with different morphologies in the high corona, for example, jet-like CMEs, bubble-like CMEs, and so-called twin CMEs that include a pair of simultaneous jet-like and bubble-like CMEs. However, what determines the morphology of a jet-related CME is still an open question. Using high spatiotemporal resolution stereoscopic observations taken by the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory from 2010 October to 2012 December, we performed a statistical study of jet-related CMEs to study the potential physical factors that determine the morphology of CMEs in the outer corona. Our statistical sample includes 16 jet-related CME events of which seven are twin CME events and nine are jet-like narrow CMEs. We find that all CMEs in our sample were accompanied by filament-driven blowout jets and Type III radio bursts during their initial formation and involved magnetic reconnection between filament channels and the surrounding magnetic fields. Most of our cases occurred in a fan-spine magnetic configuration. Our study suggests that the bubble-like components of twin CMEs lacking an obvious core are related to the expansion of the closed-loop systems next to the fan-spine topology, while the jet-like component is from the coronal extension of the jet plasma along open fields. Based on the statistical results, we conclude that the morphology of jet-related CMEs in the high corona may be related to the filament length and the initial magnetic null point height of the fan-spine structures.

Keywords: solar activity; solar coronal mass ejections; solar magnetic reconnection
Escaping Outflows from Disintegrating Exoplanets: Day-side versus Night-side Escape

Ultrahot disintegrating exoplanets have been detected with tails trailing behind and/or shooting ahead of them. These tails are believed to be made of dust that are formed out of the supersonic escaping flow that emanated from the permanent day side. Conserving angular momentum, this day-side escape flux would lead the planet in orbit. In order to explain the trailing tails in observation, radiation pressure, a repulsive force pushing the escape flow away from the host star, is considered to be necessary. We here investigate whether escape could be deflected to head away from the host star by the pressure gradient force. We demonstrate in an idealized framework that escape flux from the night side can occur, and sometimes, can be even stronger than the escape from the day-side. The night-side escape infers that escape flow could trail behind the planet in orbit by virtue of angular momentum conservation even without radiation pressure. We also find analytical approximations for both day-side and night-side escape fluxes, which may be applied to study planetary evolution of disintegrating planets.

Keywords: exoplanet evolution; exoplanet atmospheres; exoplanet surfaces; exoplanets
Demographics of the M-star Multiple Population in the Orion Nebula Cluster

We present updated results constraining multiplicity demographics for the stellar population of the Orion Nebula Cluster (ONC, a high-mass, high-density star-forming region), across primary masses 0.08-0.7 M ⊙. Our study utilizes archival Hubble Space Telescope data obtained with the Advanced Camera for Surveys using multiple filters (GO-10246). Previous multiplicity surveys in low-mass, low-density associations like Taurus identify an excess of companions to low-mass stars roughly twice that of the Galactic field and find the mass ratio distribution consistent with the field. Previously, we found the companion frequency to low-mass stars in the ONC is consistent with the Galactic field over mass ratios = 0.6-1.0 and projected separations = 30-160 au, without placing constraints on the mass ratio distribution. In this study, we investigate the companion population of the ONC with a double point-spread function (PSF) fitting algorithm sensitive to separations larger than 10 au (0.″025) using empirical PSF models. We identified 44 companions (14 new), and with a Bayesian analysis we estimate the companion frequency to low-mass stars in the ONC = 0.13 ${}_{-0.03}^{+0.05}$ and the index of the power-law fit to the mass ratio distribution = 2.08 ${}_{-0.85}^{+1.03}$ over all mass ratios and projected separations of 10-200 au. We find the companion frequency in the ONC is consistent with the Galactic field population, likely from states of high transient stellar density, and a probability of 0.002 that it is consistent with that of Taurus. We also find the ONC mass ratio distribution is consistent with the field and Taurus, potentially indicative of its primordial nature, a direct outcome of the star formation process.

Keywords: star formation; star forming regions; binary stars; visual binary stars; hubble space telescope; low mass stars
A Coronal Mass Ejection and Magnetic Ejecta Observed In Situ by STEREO-A and Wind at 55° Angular Separation

We present an analysis of in situ and remote-sensing measurements of a coronal mass ejection (CME) that erupted on 2021 February 20 and impacted both the Solar TErrestrial RElations Observatory (STEREO)-A and the Wind spacecraft, which were separated longitudinally by 55°. Measurements on 2021 February 24 at both spacecraft are consistent with the passage of a magnetic ejecta (ME), making this one of the widest reported multispacecraft ME detections. The CME is associated with a low-inclined and wide filament eruption from the Sun's southern hemisphere, which propagates between STEREO-A and Wind around E34. At STEREO-A, the measurements indicate the passage of a moderately fast (~425 km s-1) shock-driving ME, occurring 2-3 days after the end of a high speed stream (HSS). At Wind, the measurements show a faster (~490 km s-1) and much shorter ME, not preceded by a shock nor a sheath, and occurring inside the back portion of the HSS. The ME orientation measured at both spacecraft is consistent with a passage close to the legs of a curved flux rope. The short duration of the ME observed at Wind and the difference in the suprathermal electron pitch-angle data between the two spacecraft are the only results that do not satisfy common expectations. We discuss the consequence of these measurements on our understanding of the CME shape and extent and the lack of clear signatures of the interaction between the CME and the HSS.

Keywords: interplanetary physics; solar coronal mass ejections; heliosphere; interplanetary magnetic fields
On the Nature of GW190814 and Its Impact on the Understanding of Supranuclear Matter

The observation of a compact object with a mass of 2.50-2.67M⊙ on 2019 August 14, by the LIGO Scientific and Virgo collaborations (LVC) has the potential to improve our understanding of the supranuclear equation of state. While the gravitational-wave analysis of the LVC suggests that GW190814 likely was a binary black hole system, the secondary component could also have been the heaviest neutron star observed to date. We use our previously derived nuclear-physics-multimessenger astrophysics framework to address the nature of this object. Based on our findings, we determine GW190814 to be a binary black hole merger with a probability of >99.9%. Even if we weaken previously employed constraints on the maximum mass of neutron stars, the probability of a binary black hole origin is still ∼81%. Furthermore, we study the impact that this observation has on our understanding of the nuclear equation of state by analyzing the allowed region in the mass-radius diagram of neutron stars for both a binary black hole or neutron star-black hole scenario. We find that the unlikely scenario in which the secondary object was a neutron star requires rather stiff equations of state with a maximum speed of sound ${c}_{s}\geqslant \sqrt{0.6}$ times the speed of light, while the binary black hole scenario does not offer any new insight.

Keywords: compact objects; neutron stars; nuclear astrophysics; nuclear physics; neutron star cores; stellar mergers; gravitational waves
No Detectable Kilonova Counterpart is Expected for O3 Neutron Star-Black Hole Candidates

We analyze the tidal disruption probability of potential neutron star-black hole (NSBH) merger gravitational-wave (GW) events, including GW190426_152155, GW190814, GW200105_162426, and GW200115_042309, detected during the third observing run of the LIGO/Virgo Collaboration and the detectability of kilonova emission in connection with these events. The posterior distributions of GW190814 and GW200105_162426 show that they must be plunging events, and hence no kilonova signal is expected from these events. With the stiffest NS equation of state allowed by the constraint of GW170817 taken into account, the probability that GW190426_152155 and GW200115_042309 can make tidal disruption is ~24% and ~3%, respectively. However, the predicted kilonova brightness is too faint to be detected for present follow-up search campaigns, which explains the lack of electromagnetic (EM) counterpart detection after triggers of these GW events. Based on the best-constrained population synthesis simulation results, we find that disrupted events account for only ≲20% of cosmological NSBH mergers, since most of the primary BHs could have low spins. The associated kilonovae for those disrupted events will still be difficult for LSST to discover after GW triggers in the future because of their low brightness and larger distances. For future GW-triggered multimessenger observations, potential short-duration gamma-ray bursts and afterglows are more probable EM counterparts of NSBH GW events.

Keywords: gravitational waves; neutron stars; black holes