adsabs/SciX_UAT_keywords huggingface dataset:
Stellar Abundances at the Center of Early-type Galaxies with Fine Structure

Our understanding of early-type galaxies (ETGs) has grown in the past decade with the advance of full-spectrum fitting techniques used to infer the properties of the stellar populations that make up the galaxy. We present ages, central velocity dispersions, and abundance ratios relative to Fe of C, N, O, Mg, Si, Ca, Ti, Cr, Mn, Co, Ni, Cu, Sr, Ba, and Eu, derived using full-spectrum fitting techniques for three ETGs, NGC 2865, NGC 3818, and NGC 4915. Each of these three galaxies were selected because they have optical, disturbed structures (fine structure) that are linked to major merger events that occurred 1, 7, and 6 Gyr ago, respectively. Two of the ETGs, NGC 3818 and NGC 4915, show chemical signatures similar to ETGs without fine structure, which is consistent with a gas-poor merger of elliptical galaxies in which substantial star formation is not expected. For NGC 2865, we find a statistically higher abundance of Ca (an α element) and Cr and Mn (Fe-peak elements). We show that for NGC 2865, a simple gas-rich merger scenario fails to explain the larger abundance ratios compared to ETGs without fine structure. These three ETGs with fine structure exhibit a range of abundances, suggesting ETGs with fine structure can form via multiple pathways and types of galaxy mergers.

Keywords: early-type galaxies; chemical abundances; chemical enrichment; spectroscopy
Reconnection Rate and Transition from Ion-coupled to Electron-only Reconnection

Standard collisionless magnetic reconnection couples with both electron and ion dynamics. Recently, a new type of magnetic reconnection, electron-only magnetic reconnection without ion outflow, has been observed, and its reconnection rate has been found to be much higher than that in ion-coupled reconnection. In this paper, using 2D particle-in-cell simulations, we find that when the ion gyroradius is much smaller than the size of the simulation domain, magnetic reconnection is standard with ion outflows. As the ion gyroradius increases, the ion response gradually weakens, and the reconnection rate becomes higher. Electron-only reconnection occurs when the ion gyroradius is comparable to the size of the simulation domain. This trend applies to both strong and weak guide field situations. Therefore, the key factor that controls the transition from ion-coupled reconnection to electron-only reconnection is the ratio between the ion gyroradius and the size of the simulation domain. We further show that, in electron-only reconnection, when the initial electron current sheet is thinner, the reconnection rate and the electron outflow speed are higher.

Keywords: plasma physics; space plasmas; planetary magnetospheres
Silicon and Hydrogen Chemistry under Laboratory Conditions Mimicking the Atmosphere of Evolved Stars

Silicon is present in interstellar dust grains, meteorites and asteroids, and to date 13 silicon-bearing molecules have been detected in the gas phase toward late-type stars or molecular clouds, including silane and silane derivatives. In this work, we have experimentally studied the interaction between atomic silicon and hydrogen under physical conditions mimicking those in the atmosphere of evolved stars. We have found that the chemistry of Si, H, and H2 efficiently produces silane (SiH4), disilane (Si2H6) and amorphous hydrogenated silicon (a-Si:H) grains. Silane has been definitely detected toward the carbon-rich star IRC +10216, while disilane has not been detected in space yet. Thus, based on our results, we propose that gas-phase reactions of atomic Si with H and H2 are a plausible source of silane in C-rich asymptotic giant branch stars, although its contribution to the total SiH4 abundance may be low in comparison with the suggested formation route by catalytic reactions on the surface of dust grains. In addition, the produced a-Si:H dust analogs decompose into SiH4 and Si2H6 at temperatures above 500 K, suggesting an additional mechanism of formation of these species in envelopes around evolved stars. We have also found that the exposure of these dust analogs to water vapor leads to the incorporation of oxygen into Si-O-Si and Si-OH groups at the expense of SiH moieties, which implies that if this kind of grain is present in the interstellar medium, it will probably be processed into silicates through the interaction with water ices covering the surface of dust grains.

Keywords: interstellar dust; interstellar dust processes; silicate grains; laboratory astrophysics; astrochemistry
10 Yr Transformation of the Obscuring Wind in NGC 5548

A decade ago, the archetypal Seyfert-1 galaxy NGC 5548 was discovered to have undergone major spectral changes. The soft X-ray flux had dropped by a factor of 30 while new broad and blueshifted UV absorption lines appeared. This was explained by the emergence of a new obscuring wind from the accretion disk. Here we report on the striking long-term variability of the obscuring disk wind in NGC 5548 including new observations taken in 2021-2022 with the Swift Observatory and the Hubble Space Telescope's Cosmic Origins Spectrograph. The X-ray spectral hardening as a result of obscuration has declined over the years, reaching its lowest in 2022, at which point we find the broad C IV UV absorption line to have nearly vanished. The associated narrow low-ionization UV absorption lines, produced previously when shielded from the X-rays, are also remarkably diminished in 2022. We find a highly significant correlation between the variabilities of the X-ray hardening and the equivalent width of the broad C IV absorption line, demonstrating that X-ray obscuration is inherently linked to disk winds. We derive for the first time a relation between the X-ray and UV covering fractions of the obscuring wind using its long-term evolution. The diminished X-ray obscuration and UV absorption are likely caused by an increasingly intermittent supply of outflowing streams from the accretion disk. This results in growing gaps and interstices in the clumpy disk wind, thereby reducing its covering fractions.

Keywords: accretion; active galactic nuclei; broad-absorption line quasar; high resolution spectroscopy; x-ray active galactic nuclei
Directly Deriving Parameters from SDSS Photometric Images

Stellar atmospheric parameters (effective temperature, surface gravity, and metallicity) are fundamental for understanding the formation and evolution of stars and galaxies. Photometric data can provide a low-cost way to estimate these parameters, but traditional methods based on photometric magnitudes have many limitations. In this paper, we propose a novel model called Bayesian Convit, which combines an approximate Bayesian framework with a deep-learning method, namely Convit, to derive stellar atmospheric parameters from Sloan Digital Sky Survey images of stars and effectively provide corresponding confidence levels for all the predictions. We achieve high accuracy for T eff and [Fe/H], with σ(T eff) = 172.37 K and σ([Fe/H]) = 0.23 dex. For $\mathrm{log}g$ , which is more challenging to estimate from image data, we propose a two-stage approach: (1) classify stars into two categories based on their $\mathrm{log}g$ values (>4 dex or <4 dex) and (2) regress separately these two subsets. We improve the estimation accuracy of stars with $\mathrm{log}g\gt 4$ dex significantly to $\sigma (\mathrm{log}g\gt 4)=0.052$ dex, which are comparable to those based on spectral data. The final joint result is $\sigma (\mathrm{log}g)=0.41$ dex. Our method can be applied to large photometric surveys like Chinese Space Station Telescope and Large Synoptic Survey Telescope.

Keywords: astronomy image processing; stellar photometry; stellar abundances; neural networks; bayes' theorem
Long-term Dynamical Stability in the Outer Solar System. I. The Regular and Chaotic Evolution of the 34 Largest Trans-Neptunian Objects

We carried out an extensive analysis of the stability of the outer solar system, making use of the frequency analysis technique over short-term integrations of nearly 100,000 test particles, as well as a statistical analysis of 200 1 Gyr long numerical simulations, which consider the mutual perturbations of the giant planets and the 34 largest trans-Neptunian objects (we have called all 34 objects "dwarf planets," DPs, even if probably only the largest of them are true DPs). From the frequency analysis, we produced statistical diffusion maps for a wide region of the a-e phase-space plane; we also present the average diffusion time for orbits as a function of perihelion. We later turned our attention to the 34 DPs, making an individualized analysis for each of them and producing a first approximation of their future stability. From the 200 distinct realizations of the orbital evolution of the 34 DPs, we classified the sample into three categories, including 17 stable, 11 unstable, and 6 resonant objects; we also found that, statistically, two objects from the sample will leave the trans-Neptunian region within the next gigayear, most likely being ejected from the solar system, but with a nonnegligible probability of going inside the orbit of Neptune, either to collide with a giant planet or even falling to the inner solar system, where our simulations are no longer able to resolve their continuous evolution.

Keywords: dwarf planets; trans-neptunian objects; solar system; n-body simulations; kuiper belt
Magnetized Accretion Disks with Outflows for Changing-look AGNs

Changing-look active galactic nuclei (CL-AGNs) challenge the standard accretion theory, owing to their rapid variability. Recent numerical simulations have shown that, for the sub-Eddington accretion case, the disk is magnetic pressure-dominated, thermally stable, and geometrically thicker than the standard disk. In addition, outflows were found in the simulations. Observationally, high blueshifted velocities absorption lines indicate that outflows exist in AGNs. In this work, based on the simulation results, we investigate the magnetic pressure-dominated disk, and find that the accretion timescale is significantly shorter than that of the standard thin disk. However, such a timescale is still longer than that of the CL-AGNs. Moreover, if the role of outflows is taken into account, then the accretion timescale can be shortened even further. By the detailed comparison of the theoretical accretion timescale with the observations, we propose that the magnetic pressure-dominated disk incorporating outflows can be responsible for the rapid variability of CL-AGNs.

Keywords: accretion; active galactic nuclei; galaxy accretion disks; magnetic fields
The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). IV. Star Cluster Catalog

We construct a catalog of star clusters from Hubble Space Telescope images of the inner disk of the Triangulum Galaxy (M33) using image classifications collected by the Local Group Cluster Search, a citizen science project hosted on the Zooniverse platform. We identify 1214 star clusters within the Hubble Space Telescope imaging footprint of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Comparing this catalog to existing compilations in the literature, 68% of the clusters are newly identified. The final catalog includes multiband aperture photometry and fits for cluster properties via integrated light spectral energy distribution fitting. The cluster catalog's 50% completeness limit is ~1500 M ☉ at an age of 100 Myr, as derived from comprehensive synthetic cluster tests.

Keywords: star clusters; triangulum galaxy; catalogs
On the Origin of Infrared Bands Attributed to Tryptophan in Spitzer Observations of IC 348

Infrared emission features toward interstellar gas of the IC 348 star cluster in Perseus have been recently proposed to originate from the amino acid tryptophan. The assignment was based on laboratory infrared spectra of tryptophan pressed into pellets, a method which is known to cause large frequency shifts compared to the gas phase. We assess the validity of the assignment based on the original Spitzer data as well as new data from JWST. In addition, we report new spectra of tryptophan condensed in para-hydrogen matrices to compare with the observed spectra. The JWST MIRI data do not show evidence for tryptophan, despite deeper integration toward IC 348. In addition, we show that several of the lines attributed to tryptophan are likely due to instrumental artifacts. This, combined with the new laboratory data, allows us to conclude that there is no compelling evidence for the tryptophan assignment.

Keywords: interstellar medium; interstellar molecules; astrochemistry; laboratory astrophysics
Multimessenger Constraints on Magnetic Fields in Merging Black Hole-Neutron Star Binaries

The LIGO-Virgo-KAGRA Collaboration recently detected gravitational waves (GWs) from the merger of black hole-neutron star (BHNS) binary systems GW200105 and GW200115. No coincident electromagnetic (EM) counterparts were detected. While the mass ratio and BH spin in both systems were not sufficient to tidally disrupt the NS outside the BH event horizon, other, magnetospheric mechanisms for EM emission exist in this regime and depend sensitively on the NS magnetic field strength. Combining GW measurements with EM flux upper limits, we place upper limits on the NS surface magnetic field strength above which magnetospheric emission models would have generated an observable EM counterpart. We consider fireball models powered by the black hole battery mechanism, where energy is output in gamma rays over ≲1 s. Consistency with no detection by Fermi-GBM or INTEGRAL SPI-ACS constrains the NS surface magnetic field to ≲1015 G. Hence, joint GW detection and EM upper limits rule out the theoretical possibility that the NSs in GW200105 and GW200115, and the putative NS in GW190814, retain dipolar magnetic fields ≳1015 G until merger. They also rule out formation scenarios where strongly magnetized magnetars quickly merge with BHs. We alternatively rule out operation of the BH-battery-powered fireball mechanism in these systems. This is the first multimessenger constraint on NS magnetic fields in BHNS systems and a novel approach to probe fields at this point in NS evolution. This demonstrates the constraining power that multimessenger analyses of BHNS mergers have on BHNS formation scenarios, NS magnetic field evolution, and the physics of BHNS magnetospheric interactions.

Keywords: gravitational wave astronomy; neutron stars; magnetic fields; gamma-ray sources
Resonances in a Coronal Loop Driven by Torsional Alfvén Waves Propagating from the Photosphere

There is increasing evidence that magnetohydrodynamic waves play an important role in the propagation and dissipation of energy in the solar atmosphere. Here we investigate how torsional Alfvén waves driven at the photosphere can transport energy to an overlying coronal magnetic loop and explore their ability to heat the plasma. We consider a coronal loop whose feet are embedded in the partially ionized chromosphere. A broadband driver at the photosphere excites torsional Alfvén waves that propagate upward to the coronal loop. By means of numerical computations under the stationary-state assumption, we study the transmission of wave energy to the loop and the heating associated with ohmic diffusion and ion-neutral collisions. We find that wave transmission to the loop is heavily affected by the presence of cavity resonances when the frequency of the driver matches an eigenfrequency of the loop. A tremendous amount of wave energy is channeled to the coronal loop for those particular frequencies. The transmitted energy surpasses by many orders of magnitude the requirements to balance thermal radiation. However, dissipation is so weak in the coronal plasma that only a tiny percentage of the energy budget is converted into heat, which is not enough to compensate for radiative losses. Most of the energy simply leaks back to the chromosphere. Conversely, dissipation is much more efficient in the lower atmosphere, and wave heating can locally balance a significant fraction of radiation in the chromosphere. We argue that nonlinear effects such as turbulence triggered by the Kelvin-Helmholtz instability should enhance the heating efficiency at coronal heights.

Keywords: solar physics
Further Evidence of Modified Spin-down in Sun-like Stars: Pileups in the Temperature-Period Distribution

We combine stellar surface rotation periods determined from NASA's Kepler mission with spectroscopic temperatures to demonstrate the existence of pileups at the long-period and short-period edges of the temperature-period distribution for main-sequence stars with temperatures exceeding ~5500 K. The long-period pileup is well described by a curve of constant Rossby number, with a critical value of Rocrit ≲ Ro⊙. The long-period pileup was predicted by van Saders et al. as a consequence of weakened magnetic braking, in which wind-driven angular momentum losses cease once stars reach a critical Rossby number. Stars in the long-period pileup are found to have a wide range of ages (~2-6 Gyr), meaning that, along the pileup, rotation period is strongly predictive of a star's surface temperature but weakly predictive of its age. The short-period pileup, which is also well described by a curve of constant Rossby number, is not a prediction of the weakened magnetic braking hypothesis but may instead be related to a phase of slowed surface spin-down due to core-envelope coupling. The same mechanism was proposed by Curtis et al. to explain the overlapping rotation sequences of low-mass members of differently aged open clusters. The relative dearth of stars with intermediate rotation periods between the short- and long-period pileups is also well described by a curve of constant Rossby number, which aligns with the period gap initially discovered by McQuillan et al. in M-type stars. These observations provide further support for the hypothesis that the period gap is due to stellar astrophysics, rather than a nonuniform star formation history in the Kepler field.

Keywords: stellar rotation; solar analogs; stellar evolution; stellar magnetic fields; stellar winds
Direct Measurement of the Solar-wind Taylor Microscale Using MMS Turbulence Campaign Data

Using the novel Magnetospheric Multiscale (MMS) mission data accumulated during the 2019 MMS Solar Wind Turbulence Campaign, we calculate the Taylor microscale (λT) of the turbulent magnetic field in the solar wind. The Taylor microscale represents the onset of dissipative processes in classical turbulence theory. However, an accurate estimation of the Taylor scale from spacecraft data is usually difficult due to low time cadence, the effect of time decorrelation, and other factors. Previous reports were based either entirely on the Taylor frozen-in approximation, which conflates time dependence, or were obtained using multiple data sets, which introduces sample-to-sample variation of plasma parameters, or had interspacecraft distances that were larger than the present study. The unique configuration of linear formation with logarithmic spacing of the four MMS spacecraft, during the campaign, enables a direct evaluation of the λT from a single data set, independent of the Taylor frozen-in approximation. A value of λT ≈ 7000 km is obtained, which is about three times larger than the previous estimates.

Keywords: interplanetary turbulence; solar wind; space plasmas; magnetohydrodynamics; plasma astrophysics
Predicting Stellar Masses of the First Galaxies Using Graph Neural Networks

Theoretical models of galaxy formation and evolution are primarily investigated through cosmological simulations and semi-analytical models. The former method consumes ${ \mathcal O }({10}^{6})$ core-hours explicitly modeling the dynamics of the galaxies, whereas the latter method only requires ${ \mathcal O }({10}^{3})$ core-hours foregoing directly simulating internal structure for computational efficiency. In this work, we present a proof-of-concept machine learning regression model, using a graph neural network architecture, to predict the stellar mass of high-redshift galaxies solely from their dark matter merger trees, trained from a radiation hydrodynamics cosmological simulation of the first galaxies.

Keywords: neural networks; high-redshift galaxies; galaxies; dark matter; stellar masses
Mass Estimation of Galaxy Clusters with Deep Learning. I. Sunyaev-Zel'dovich Effect

We present a new application of deep learning to infer the masses of galaxy clusters directly from images of the microwave sky. Effectively, this is a novel approach to determining the scaling relation between a cluster's Sunyaev-Zel'dovich (SZ) effect signal and mass. The deep-learning algorithm used is mResUNet, which is a modified feed-forward deep-learning algorithm that broadly combines residual learning, convolution layers with different dilation rates, image regression activation, and a U-Net framework. We train and test the deep-learning model using simulated images of the microwave sky that include signals from the cosmic microwave background, dusty and radio galaxies, and instrumental noise as well as the cluster's own SZ signal. The simulated cluster sample covers the mass range 1 × 1014 M⊙ < M200c < 8 × 1014 M⊙ at z = 0.7. The trained model estimates the cluster masses with a 1σ uncertainty ΔM/M ≤ 0.2, consistent with the input scatter on the SZ signal of 20%. We verify that the model works for realistic SZ profiles even when trained on azimuthally symmetric SZ profiles by using the Magneticum hydrodynamical simulations.

Keywords: galaxy clusters; cosmic microwave background radiation; convolutional neural networks; sunyaev-zeldovich effect; large-scale structure of the universe; sky surveys
Effects of Multiscale Plasma Waves on Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks

Radio relics associated with merging galaxy clusters indicate the acceleration of relativistic electrons in merger-driven shocks with low sonic Mach numbers (Ms ≲ 3) in the intracluster medium (ICM). Recent studies have suggested that electron injection to diffusive shock acceleration (DSA) could take place through the so-called Fermi-like acceleration in the shock foot of β = Pgas/PB ≈ 20-100 shocks and the stochastic shock drift acceleration (SSDA) in the shock transition of β ≈ 1-5 shocks. Here, we explore how the SSDA can facilitate electron preacceleration in weak quasi-perpendicular (Q⊥) shocks in β ≈ 20-100 plasmas by performing particle-in-cell simulations in a two-dimensional domain large enough to properly encompass ion-scale waves. We find that in supercritical shocks with ${M}_{{\rm{s}}}\gtrsim {M}_{\mathrm{AIC}}^{* }\sim 2.3$ , multiscale waves are excited by the ion and electron temperature anisotropies in the downstream of the shock ramp, and that through stochastic pitch-angle scattering off the induced waves, electrons are confined in the shock transition for an extended period. Gaining energy through the gradient-drift along the motional electric field, electrons could be preaccelerated all the way to injection to DSA at such ICM shocks. Our findings imply that the electron DSA process at weak ICM shocks could explain the origin of radio relics. However, a further investigation of electron acceleration at subcritical shocks with Ms < 2.3 is called for, since the Mach numbers of some observed radio relic shocks derived from radio or X-ray observations are as low as Ms ~ 1.5.

Keywords: shocks; cosmic rays; galaxy clusters