adsabs/SciX_UAT_keywords huggingface dataset:
Multiple Emission Lines of Hα Emitters at z ∼ 2.3 from the Broad- and Medium-band Photometry in the ZFOURGE Survey

We present a multiple emission line study of ∼1300 Hα emitters (HAEs) at z ∼ 2.3 in the ZFOURGE survey. In contrast to the traditional spectroscopic method, our sample is selected based on the flux excess in the ZFOURGE K s broadband data relative to the best-fit stellar continuum. Using the same method, we also extract the strong diagnostic emission lines for these individual HAEs: [O III] λ λ4959, 5007 and [O II] λ λ3726, 3729. Our measurements demonstrate good consistency with those obtained from spectroscopic surveys. We investigate the relationship between the equivalent widths (EWs) of these emission lines and various galaxy properties, including stellar mass, stellar age, star formation rate, specific star formation rate, and ionization state (O32). We have identified a discrepancy between HAEs at z ∼ 2.3 and typical local star-forming galaxies observed in the Sloan Digital Sky Survey, suggesting the evolution of lower gas-phase metallicity (Z) and higher ionization parameters (U) with redshift. Notably, we have observed a significant number of low-mass HAEs exhibiting exceptionally high EW[O III]. Their galaxy properties are comparable to those of extreme objects, such as extreme O3 emitters and Lyα emitters at z ≃ 2–3. Considering that these characteristics may indicate potential strong Lyman continuum leakage, higher-redshift analogs of the low-mass HAEs could be significant contributors to the cosmic reionization. Further investigations of this particular population are required to gain a clearer understanding of galaxy evolution and cosmic reionization.

Keywords: high-redshift galaxies; emission line galaxies; galaxy evolution
Stellar Collisions in the Galactic Center: Massive Stars, Collision Remnants, and Missing Red Giants

Like most galaxies, the Milky Way harbors a supermassive black hole (SMBH) at its center, surrounded by a nuclear star cluster. In this dense star cluster, direct collisions can occur between stars before they evolve off the main sequence. Using a statistical approach, we characterize the outcomes of these stellar collisions within the inner parsec of the Galactic center (GC). Close to the SMBH, where the velocity dispersion is larger than the escape speed from a Sun-like star, collisions lead to mass loss. We find that the stellar population within 0.01 pc is halved within about a billion years because of destructive collisions. Additionally, we predict a diffuse population of peculiar low-mass stars in the GC. These stars have been divested of their outer layers in the inner 0.01 pc before migrating to larger distances from the SMBH. Between 0.01 and 0.1 pc from the SMBH, collisions can result in mergers. Our results suggest that repeated collisions between lower-mass stars can produce massive (≳10 M ⊙) stars, and that there may be ~100 of them residing in this region. We provide predictions on the number of so-called G objects, dust- and gas-enshrouded stellar objects, that may result from main-sequence stellar collisions. Lastly, we comment on uncertainties in our model and possible connections between stellar collisions and the missing red giants in the GC.

Keywords: stellar dynamics; galactic center; star clusters; stellar mergers
Chasing Accreted Structures within Gaia DR2 Using Deep Learning

In previous work, we developed a deep neural network classifier that only relies on phase-space information to obtain a catalog of accreted stars based on the second data release of Gaia (DR2). In this paper, we apply two clustering algorithms to identify velocity substructure within this catalog. We focus on the subset of stars with line-of-sight velocity measurements that fall in the range of Galactocentric radii $r\in [6.5,9.5]\,{\rm{kpc}}$ and vertical distances $| z| \lt 3\,{\rm{kpc}}$ . Known structures such as Gaia Enceladus and the Helmi stream are identified. The largest previously unknown structure, Nyx, is a vast stream consisting of at least 200 stars in the region of interest. This study displays the power of the machine-learning approach by not only successfully identifying known features but also discovering new kinematic structures that may shed light on the merger history of the Milky Way.

Keywords: milky way dynamics; galaxy dynamics; astrometry; neural networks; star clusters
A Census of the Extended Neutral Hydrogen around 18 MHONGOOSE Galaxies

We present the analysis of the diffuse, low column density H I environment of 18 MHONGOOSE galaxies. We obtained deep observations with the Robert C. Byrd Green Bank Telescope and reached down to a 3σ column density detection limit of NHI = 6.3 × 1017 cm-2 over a 20 km s-1 line width. We analyze the environment around these galaxies, with a focus on H I gas that reaches column densities below NHI = 1019 cm-2. We calculate the total amount of H I gas in and around the galaxies, revealing that nearly all of these galaxies contained excess H I outside of their disks. We quantify the amount of diffuse gas in the maps of each galaxy, defined by H I gas with column densities below 1019 cm-2, and find a large spread in percentages of diffuse gas. However, by binning the percentage of diffuse H I into quarters, we find that the bin with the largest number of galaxies is the lowest quartile (0%-25% diffuse H I). We identified several galaxies that may be undergoing gas accretion onto the galaxy disk using multiple methods of analysis, including azimuthally averaging column densities beyond the disk, and identifying structure within our integrated intensity (moment 0) maps. We measured H I mass outside the disks of most of our galaxies, with rising cumulative flux even at large radii. We also find a strong correlation between the fraction of diffuse gas in a galaxy and its baryonic mass, and we test this correlation using both Spearman and Pearson correlation coefficients. We see evidence of a dark matter halo mass threshold of Mhalo ∼ 1011.1 M⊙ in which galaxies with high fractions of diffuse H I all reside below. It is in this regime that cold-mode accretion should dominate. Finally, we suggest a rotation velocity of vrot ∼ 80 km s-1 as an upper threshold to find diffuse-gas-dominated galaxies.

Keywords: circumgalactic medium; extragalactic astronomy; galaxy evolution; galaxy accretion; galaxy structure
Gas-dynamical Mass Measurements of the Supermassive Black Holes in the Early-type Galaxies NGC 4786 and NGC 5193 from ALMA and HST Observations

We present molecular gas-dynamical mass measurements of the central black holes in the giant elliptical galaxies NGC 4786 and NGC 5193, based on CO (2‑1) observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope near-infrared imaging. The central region in each galaxy contains a circumnuclear disk that exhibits orderly rotation with projected line-of-sight velocities of ∼270 km s‑1. We build gas-dynamical models for the rotating disk in each galaxy and fit them directly to the ALMA data cubes. At 0.″31 resolution, the ALMA observations do not fully resolve the black hole sphere of influence (SOI), and neither galaxy exhibits a central rise in rotation speed, indicating that emission from deep within the SOI is not detected. As a result, our models do not tightly constrain the central black hole mass in either galaxy, but they prefer the presence of a central massive object in both galaxies. We measure the black hole mass to be $({M}_{\mathrm{BH}}/{10}^{8}\,{M}_{\odot })=5.0\pm 0.2\,[1\sigma \,\mathrm{statistical}]{\,}_{-1.3}^{+1.4}\,[\mathrm{systematic}]$ in NGC 4786 and $({M}_{\mathrm{BH}}/{10}^{8}\,{M}_{\odot })=1.4\pm 0.03\,[1\sigma \,\mathrm{statistical}{]}_{-0.1}^{+1.5}\,[\mathrm{systematic}]$ in NGC 5193. The largest component of each measurement's error budget is from the systematic uncertainty associated with the extinction correction in the host galaxy models. This underscores the importance of assessing the impact of dust attenuation on the inferred M BH. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs 15226 and 15909.

Keywords: supermassive black holes; millimeter astronomy; submillimeter astronomy; astronomy data modeling; molecular gas; early-type galaxies; galaxy kinematics
Distinguishing Active Galactic Nuclei Feedback Models with the Thermal Sunyaev-Zel'dovich Effect

Current models of galaxy formation require strong feedback from active galactic nuclei (AGN) to explain the observed lack of star formation in massive galaxies since z ≈ 2, but direct evidence of this energy input is limited. We use the SIMBA cosmological galaxy formation simulations to assess the ability of thermal Sunyaev-Zel'dovich (tSZ) measurements to provide such evidence, by mapping the pressure structure of the circumgalactic medium around massive z ≈ 0.2-1.5 galaxies. We undertake a stacking approach to calculate the total tSZ signal and its radial profile in simulations with varying assumptions of AGN feedback, and we assess its observability with current and future telescopes. By convolving our predictions with the 2.'1 beam of the Atacama Cosmology Telescope, we show that current observations at z ≈ 1 are consistent with SIMBA's fiducial treatment of AGN feedback and inconsistent with SIMBA models without feedback. At z ≈ 0.5, observational signals lie between SIMBA run with and without AGN feedback, suggesting AGN in SIMBA may inject too much energy at late times. By convolving our data with a 9.″5 beam corresponding to the TolTEC camera on the Large Millimeter Telescope Alfonso Serrano, we predict a unique profile for AGN feedback that can be distinguished with future higher-resolution measurements. Finally, we explore a novel approach to quantify the nonspherically symmetric features surrounding our galaxies by plotting radial profiles representing the component of the stack with m-fold symmetry.

Keywords: sunyaev-zeldovich effect; cosmic microwave background radiation; galaxy evolution; quasars; large-scale structure of the universe; hydrodynamical simulations; intergalactic medium; extragalactic astronomy
A Model to Predict the Size of Regolith Clumps on Planetary Bodies

Prior investigations of the behavior of regolith on the surface of planetary bodies has considered the motion and interactions of individual grains. Recent work has shown the significance of cohesion in understanding the behavior of planetary regolith, especially on small, airless bodies. Surficial regolith grains may detach from a planetary body due to a variety of phenomena, including aeolian effects, spacecraft operations, micrometeoroid bombardment, and electrostatic lofting. It is well known in terrestrial powder handling that cohesive powders tend to form clumps. We present a theory for the size of regolith clumps that are likely to form and be easier to detach from a surface than their constituent grains, assuming monodisperse, spherical grains. The model predictions are significant for our interpretation of the surface of asteroids, as well as understanding a variety of phenomena on planetary bodies and designing of sampling spacecraft.

Keywords: asteroid surfaces
The JWST Resolved Stellar Populations Early Release Science Program. II. Survey Overview

We present the JWST Resolved Stellar Populations Early Release Science (ERS) program. We obtained 27.5 hr of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultrafaint dwarf galaxy Draco II, and star-forming dwarf galaxy WLM), which span factors of ~105 in luminosity, ~104 in distance, and ~105 in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color-magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen-burning limit in M92 (<0.08 M ⊙; M F090W ~ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 M ⊙; M F090W ~ +12.1), and reach ~1.5 mag below the oldest main-sequence turnoff in WLM (M F090W ~ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though they are ~0.05 mag too blue compared to M92 F090W - F150W data. Our CMDs show detector-dependent color offsets ranging from ~0.02 mag in F090W - F150W to ~0.1 mag in F277W - F444W; these appear to be due to differences in the zero-point calibrations among the detectors. The NIRCam ETC (v2.0) matches the signal-to-noise ratios based on photon noise in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for the Hubble Space Telescope. We release the point-source photometry package DOLPHOT, optimized for NIRCam and NIRISS, for the community.

Keywords: stellar photometry; local group; stellar populations; hertzsprung russell diagram; james webb space telescope
Benzene Vapor Pressures at Titan Temperatures: First Microbalance Results

The vapor pressure of crystalline benzene (C6H6) has been measured for the first time with a quartz-crystal microbalance under ultrahigh vacuum conditions from about 135 to 160 K, temperatures relevant for Titan's atmosphere. Good agreement is found with the most recent thermodynamic analysis of higher-temperature literature results, but there is less satisfactory agreement with recently published low-temperature data obtained with a different laboratory method. An enthalpy of sublimation of 49.7 ± 0.1 kJ mol-1 for benzene is reported, and a few brief comments are made concerning the connections between our new data and Titan's atmosphere. Supporting our benzene results are new vapor-pressure measurements for crystalline H2O ice and crystalline cyclohexane (C6H12). The latter are the first of their type and enable the two sets of recently published vapor pressures for solid benzene to be brought into close agreement.

Keywords: titan; astrochemistry; experimental techniques
A CO Survey of SpARCS Star-forming Brightest Cluster Galaxies: Evidence for Uniformity in BCG Molecular Gas Processing across Cosmic Time

We present ALMA CO (2-1) detections of 24 star-forming brightest cluster galaxies (BCGs) over 0.2 < z < 1.2, constituting the largest and most distant sample of molecular gas measurements in BCGs to date. The BCGs are selected from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) to be IR-bright and therefore star-forming. We find that molecular gas is common in star-forming BCGs, detecting CO at a detection rate of 80% in our target sample of 30 objects. We additionally provide measurements of the star formation rate and stellar mass, calculated from existing MIPS 24 μm and IRAC 3.6 μm fluxes, respectively. We find these galaxies have molecular gas masses of 0.7-11.0 × 1010 M⊙, comparable to other BCGs in this redshift range, and specific star formation rates that trace the main sequence of Elbaz et al. We compare our BCGs to those of the lower-redshift, cooling-flow BCG sample assembled by Edge and find that at z ≲ 0.6 the two samples show very similar correlations between their gas masses and specific SFRs. We suggest that, in this redshift regime, the ∼10% of BCGs that are star-forming process accreted molecular gas into stars through means that are agnostic to both their redshift and their cluster mass.

Keywords: galaxy clusters; galactic and extragalactic astronomy; brightest cluster galaxies; galaxy evolution; molecular gas
Condensation of Atomic Carbon: Possible Routes toward Glycine

Many organic molecules including amino acids and nucleobases are expected to be formed in astrophysical environments. In this article, we used both experimental and computational approaches to test the possibility of the glycine formation in the interstellar medium via C atom addition to ice mantels of dust particles. The reactions of C atoms with NH3 and H2 were studied experimentally. These reactions are found to be highly exothermic and barrierless, leading to the formation of the products CH2NH and HCH. These product molecules are formed in excited states and therefore could immediately take part even in chemical reactions with energy barriers. The CH2NH molecule is formed in the long-lived triplet state, which is above the most energetically favorable singlet state of about 20,918 cm-1 (∼250 kJ mol-1). Therefore, based on the results of quantum chemical computations the following two pathways can take place at low temperature. The first one is C + H2 → HCH followed by NH3 + HCH + CO2 → glycine. The second one is C + NH3 → CH2NH followed by CH2NH + CO + H2O → glycine or CH2NH + CO2 + H2 → glycine. The first pathway was also tested experimentally by adding C atoms to ice clusters containing H2, NH3, and CO2 molecules. The detection of the main mass peak of glycine supported the feasibility of the proposed pathway.

Keywords: interstellar dust processes; astrophysical dust processes; pre-biotic astrochemistry; astrochemistry; astrobiology; dark interstellar clouds
On the Seasonal Variations of the Ion Precipitation Down to the Upper Atmosphere of Mars

We investigate the seasonal variations of ion precipitation, utilizing observations from the Mars Atmosphere and Volatile Evolution mission spanning from 2014 January 4 to 2023 February 14. Our analysis reveals that a diminishing pattern characterizes the transition from Mars season L s 0°-180° to Mars season L s 180°-360°, manifesting as a reduction in precipitating ion fluxes. Additionally, we discern a significant influence of the crustal magnetic field on the seasonal variations in precipitating ion fluxes. Intriguingly, within regions where the crustal magnetic field exhibits a strong quasi-horizontal orientation, opposite seasonal trends become evident. The underlying physical mechanism driving these seasonal variations in ion precipitation is probably attributed to the mass loading effect that may decelerate the solar wind and influence the magnetic pileup. A detailed investigation is further demanded in the future.

Keywords: mars; planetary ionospheres; planetary atmospheres
Wrinkles in Time. I. Rapid Rotators Found in High-eccentricity Orbits

Recent space-based missions have ushered in a new era of observational astronomy, where high-cadence photometric light curves for thousands to millions of stars in the solar neighborhood can be used to test and apply stellar age-dating methods, including gyrochronology. Combined with precise kinematics, these data allow for powerful new insights into our understanding of the Milky Way's dynamical history. Using TESS data, we build a series of rotation period measurement and confirmation pipelines and test them on 1560 stars across five benchmark samples: the Pleiades, Pisces-Eridanus, Praesepe, the Hyades, and field stars from the MEarth Project. Our pipelines' recovery rates across these groups are, on average, 89%. We then apply these pipelines to 4085 likely single stars with TESS light curves in two interesting regions of Galactic action space. We identify 141 unique, rapidly rotating stars in highly eccentric orbits in the disk, some of which appear as rotationally young as the 120 Myr old Pleiades. Pending spectroscopic analysis to confirm their youth, this indicates that these stars were subject to fast-acting dynamical phenomena, the origin of which will be investigated in later papers in this series.

Keywords: stellar rotation; milky way dynamics; stellar kinematics; stellar ages
Alternative High-plasma Beta Regimes of Electron Heat-flux Instabilities in the Solar Wind

Heat transport in the solar wind is dominated by suprathermal electron populations, i.e., a tenuous halo and a field-aligned beam/strahl, with high energies and antisunward drifts along the magnetic field. Their evolution may offer plausible explanations for the rapid decrease of the heat flux with the solar wind expansion, and self-generated instabilities, or so-called "heat flux instabilities" (HFIs), are typically invoked to explain this evolution. This Letter provides a unified description of the full spectrum of HFIs, as prescribed by the linear kinetic theory for high beta conditions (βe ≫ 0.1) and different relative drifts (U) of the suprathermals. HFIs of different natures are examined, i.e., electromagnetic, electrostatic or hybrid, propagating parallel or obliquely to the magnetic field, etc., as well as their regimes of interplay (co-existence) or dominance. These alternative regimes of HFIs complement each other and may be characteristic of different relative drifts of suprathermal electrons and various conditions in the solar wind, e.g., in the slow or fast winds, streaming interaction regions, and interplanetary shocks. Moreover, these results strongly suggest that heat flux regulation may not involve just one but several HFIs, concomitantly or successively in time. Conditions for a single, well-defined instability with major effects on the suprathermal electrons and, implicitly, the heat flux, seem to be very limited. Whistler HFIs are more likely to occur but only for minor drifts (as also reported by recent observations), which may explain a modest implication in their regulation, shown already in quasilinear studies and numerical simulations.

Keywords: solar wind; plasma astrophysics; space plasmas
Puffed-up Edges of Planet-opened Gaps in Protoplanetary Disks. I. Hydrodynamic Simulations

Dust gaps and rings appear ubiquitous in bright protoplanetary disks. Disk-planet interaction with dust trapping at the edges of planet-induced gaps is one plausible explanation. However, the sharpness of some observed dust rings indicate that sub-millimeter-sized dust grains have settled to a thin layer in some systems. We test whether or not such dust around gas gaps opened by planets can remain settled by performing three-dimensional, dust-plus-gas simulations of protoplanetary disks with an embedded planet. We find planets massive enough to open gas gaps stir small, sub-millimeter-sized dust grains to high disk elevations at the gap edges, where the dust scale height can reach ∼70% of the gas scale height. We attribute this dust "puff up" to the planet-induced meridional gas flows previously identified by Fung & Chiang and others. We thus emphasize the importance of explicit 3D simulations to obtain the vertical distribution of sub-millimeter-sized grains around gas gaps opened by massive planets. We caution that the gas-gap-opening planet interpretation of well-defined dust rings is only self-consistent with large grains exceeding millimeter size.

Keywords: planet formation; hydrodynamical simulations; protoplanetary disks; interstellar dust