adsabs/SciX_UAT_keywords huggingface dataset:
Minor Merger Growth in Action: JWST Detects Faint Blue Companions around Massive Quiescent Galaxies at 0.5 ≤ z ≤ 3.0

Minor mergers are thought to drive the structural evolution of massive quiescent galaxies; however, existing Hubble Space Telescope (HST) imaging is primarily sensitive to stellar mass ratios ≳1:10. Here, we report the discovery of a large population of low-mass companions within 35 kpc of known $\mathrm{log}{M}_{* }/{M}_{\odot }\gtrsim 10.5$ quiescent galaxies at 0.5 ≤ z ≤ 3. While massive companions like those identified by HST are rare, JWST imaging from the JWST Advanced Deep Extragalactic Survey reveals that the average massive quiescent galaxy hosts approximately five nearby companions with stellar mass ratios <1:10. Despite a median stellar mass ratio of just 1:900, these tiny companions are so numerous that they represent at least 30% of the total mass being added to quiescent galaxies via minor mergers. While relatively massive companions have colors similar to their hosts, companions with mass ratios <1:10 typically have bluer colors and lower mass-to-light ratios than their host galaxies at similar radii. The accretion of these tiny companions is likely to drive evolution in the color gradients and stellar population properties of the host galaxies. Our results suggest that the well-established "minor merger growth" model for quiescent galaxies extends down to very low mass ratios of ≲1:100, and demonstrates the power of JWST to constrain both the spatially resolved properties of massive galaxies and the properties of low-mass companions beyond the local Universe.

Keywords: galaxy evolution; galaxy formation; galaxy structure; elliptical galaxies; high-redshift galaxies
The Transient Outgassed Atmosphere of 55 Cancri e

T​​​​​​he enigmatic nature of 55 Cancri e has defied theoretical explanation. Any explanation needs to account for the observed variability of its secondary eclipse depth, which is at times consistent with zero in the visible/optical range of wavelengths-a phenomenon that does not occur with its also variable infrared eclipses. Yet despite this variability, its transit depth remains somewhat constant in time and is inconsistent with opaque material filling its Hill sphere. The current study explores the possibility of a thin, transient, secondary atmosphere on 55 Cancri e that is sourced by geochemical outgassing. Its transient nature derives from the inability of outgassing to be balanced by atmospheric escape. As the outgassed atmosphere escapes and is replenished, it rapidly adjusts to radiative equilibrium and the temperature fluctuations cause the infrared eclipse depths to vary. Atmospheres of pure carbon dioxide or carbon monoxide produce sufficient Rayleigh scattering to explain the observed optical/visible eclipse depths, which vanish in the absence of an atmosphere and the presence of a dark rocky surface. Atmospheres of pure methane are ruled out, because they produce insufficient Rayleigh scattering. Upcoming observations by the James Webb Space Telescope will potentially allow the atmospheric temperature and surface pressure, as well as the surface temperature, to be measured.

Keywords: exoplanets
Variability in Titan's Mesospheric HCN and Temperature Structure as Observed by ALMA

The temperature structure of Titan's upper atmosphere exhibits large variability resulting from numerous spatially and temporally irregular external energy sources, seasonal changes, and the influence of molecular species produced via photochemistry. In particular, Titan's relatively abundant HCN is thought to provide substantial cooling to the upper atmosphere through rotational emission, balancing UV/EUV heating, and thermal conduction. Here we present the analysis of ALMA observations of Titan from 2012, 2014, 2015, and 2017, corresponding to planetocentric solar longitudes of ~34°-89°, including vertical HCN and temperature profiles retrieved from the lower mesosphere through the thermosphere (~350-1200 km; 3 × 10-2-2 × 10-8 mbar). Throughout the atmosphere, temperature profiles differ by 10 to 30 K between observations approximately 1 Earth yr apart, particularly from 600 to 900 km. We find evidence for a large imbalance in Titan's upper atmospheric energy budget between 2014 and 2015, where the mesospheric thermal structure changes significantly and marks the transition between a mesopause located at ~600 km (2 × 10-4 mbar) and ~800 km (3 × 10-6 mbar). The retrieved HCN abundances vary dramatically during the 2012-2017 time period as well, showing close to 2 orders of magnitude difference in abundance at 1000 km. However, the change in HCN abundance does not appear to fully account for the variation in mesospheric temperatures over the L S ~ 34°-89° period. These measurements provide additional insight into the variability of Titan's mesospheric composition and thermal structure following its 2009 vernal equinox and motivate continued investigation of the origins of such rapid changes in Titan's atmosphere throughout its seasonal cycle.

Keywords: titan; natural satellite atmospheres; radiative transfer; submillimeter astronomy; planetary science; solar system astronomy; planetary atmospheres; remote sensing; astrochemistry
Enhanced Size Uniformity for Near-resonant Planets

Super-Earths within the same close-in, compact planetary system tend to exhibit a striking degree of uniformity in their radius, mass, and orbital spacing, and this "peas-in-a-pod" phenomenon itself serves to provide one of the strongest constrains on planet formation at large. While it has been recently demonstrated from independent samples that such planetary uniformity occurs for both configurations near and distant from mean motion resonance, the question thus remains if the strength of this uniformity itself differs between near-resonant and nonresonant configurations such that the two modes may be astrophysically distinct in their evolution. We thus provide in this work a novel comparative size uniformity analysis for 48 near-resonant and 251 nonresonant multiplanet systems from the California Kepler Survey catalog, evaluating uniformity both across systems and between planetary pairs within the same system. We find that while multiplanet configurations exhibit strong peas-in-a-pod size uniformity regardless of their proximity to resonance, near-resonant configurations display enhanced intra-system size uniformity as compared to their analogous nonresonant counterparts at the level of both entire systems and subsystem planetary pairs and chains. These results are broadly consistent with a variety of formation paradigms for multiple-planet systems, such as convergent migration within a turbulent protoplanetary disk or planet-planet interactions incited by postnebular dynamical instabilities. Nevertheless, further investigation is necessary to ascertain whether the nonresonant and near-resonant planetary configurations respectively evolve via a singular process or mechanisms that are dynamically distinct.

Keywords: exoplanet astronomy; exoplanets; exoplanet systems; exoplanet dynamics; super earths; orbital resonances; exoplanet evolution
A Disk Instability Model for the Quasi-periodic Eruptions of GSN 069

GSN 069 is a recently discovered quasi-periodic eruption (QPE) source recurring about every 9 hr. The mechanism for the QPEs of GSN 069 is still unclear. In this work, a disk instability model is constructed to explain GSN 069 based on Pan et al. (PLC21), where the authors proposed a toy model for the repeating changing-look active galactic nuclei. We improve the work of PLC21 by including a nonzero viscous torque condition on the inner boundary of the disk and adopting a general form for the viscous stress torque in the Kerr metric. It is found that the 0.4-2 keV light curves, the light curves at different energy bands, and the phase-resolved X-ray spectrum of GSN 069 can all be qualitatively reproduced by our model. Furthermore, the profiles of light curves in QPEs can be significantly changed by the parameter μ in the viscous torque equation, which implies that our model may also be applied to other QPEs.

Keywords: magnetic fields; galaxy accretion disks; active galactic nuclei
DiskMINT: A Tool to Estimate Disk Masses with CO Isotopologues

CO is one of the most abundant molecules in protoplanetary disks, and optically thin emission from its isotopologues has been detected in many of them. However, several past works have argued that reproducing the relatively low emission of CO isotopologues requires a very low disk mass or significant CO depletion. Here, we present a Python code, DiskMINT, which includes gas density and temperature structures that are both consistent with the thermal pressure gradient, isotope-selective chemistry, and conversion of CO into CO2 ice on grain surfaces. The code generates a self-consistent disk structure, where the gas disk distribution is obtained from a spectral energy distribution (SED)-derived dust disk structure with multiple grain sizes. We use DiskMINT to study the disk of RU Lup, a high-accreting star whose disk was previously inferred to have a gas mass of only ~1.5 × 10-3 M ⊙ and gas-to-dust mass ratio of ~4. Our best-fit model to the long-wavelength continuum emission can explain the total C18O luminosity as well as the C18O velocity and radial intensity profiles, and it obtains a gas mass of ~1.2 × 10-2 M ⊙, an order of magnitude higher than previous results. A disk model with parametric Gaussian vertical distribution that better matches the IR SED can also explain the observables above with a similarly high gas mass ~2.1 × 10-2 M ⊙. We confirm the conclusions of Ruaud et al. that optically thin C18O rotational lines provide reasonable estimates of the disk mass and can therefore be used as gas disk tracers.

Keywords: protoplanetary disks; astrochemistry; chemical abundances; co line emission; planet formation
Neutrino Pair Annihilation above Black Hole Accretion Disks in Modified Gravity

Using idealized models of the accretion disk, we investigate the effects induced by the modified theories of gravity on the annihilation of the neutrino pair annihilation into electron-positron pairs ( $\nu \bar{\nu }\to {e}^{-}{e}^{+}$ ), occurring near the rotational axis. For the accretion disk, we have considered the models with temperature T = constant and T ∝ r -1. In both cases, we find that the modified theories of gravity lead to an enhancement, up to more than 1 order of magnitude with respect to general relativity, of the neutrino pair annihilation.

Keywords: neutrino astronomy; high energy astrophysics; gamma-ray bursts; general relativity; gravitation; neutron stars; non-standard theories of gravity
Lessons from the First Multiply Imaged Supernova: Revised Strong-lensing Models for the Galaxy Cluster MACS J1149.5+2223

We present two grid-based lens models for the galaxy cluster MACS J1149.5+2223, concentrating on the properties of the first multiply imaged supernova Refsdal, which first appeared in this cluster as an Einstein cross (images S1-S4) around a cluster galaxy in late 2014, and about a year later as an additional image (SX) in a different image of the supernova (SN) host galaxy. One model is our updated light-traces-mass (LTM) strong-lensing model for this cluster, and the second is a parametric model (dPIEeNFW), generated using the same pipeline but with a different parameterization. Together these two models probe different possible solutions in a relatively self-consistent manner and can be used to examine systematic uncertainties and relevant differences between the two parameterizations. We obtain reasonably similar (agreeing to within ≃1σ-3σ, in most cases) time delays and magnification ratios, with respect to S1, from the two different methods, although the LTM predictions seem to be systematically shorter/smaller for some of the images. Most notably, the time delay [and 95% CI] between the Einstein cross (in particular, image S1), and SX, differs substantially between the parametric method (326 [300-359] days) and the LTM method (224 [198-306] days), which seems to underestimate the true reappearance time. The cause for this systematic difference is unclear at present. We speculate on its possible origin and note that a refined measurement of SN Refsdal's properties should help to more strongly discriminate between the two solutions, and thus between the two descriptions for the intrinsic shape of the underlying matter distribution. We also discuss the implications of our results for the Hubble constant.

Keywords: dark matter; cosmology; navarro-frenk-white profile; observational cosmology; galaxy clusters; gravitational lensing; strong gravitational lensing; cosmological parameters; hubble constant
H I Absorption in Low-power Radio AGNs Detected by FAST

We report the discovery of three H I absorbers toward low-power radio active galactic nuclei (AGNs) in a pilot H I absorption survey with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Compared to past studies, FAST observations have explored lower radio powers by ~0.4 dex and detected these weakest absorbers at given redshifts. By comparing the gas properties and kinematics of sources along radio powers, we aim to explore the interplay between AGN and the surrounding interstellar medium (ISM). Compared to brighter sources at similar redshifts, our observations suggest a slightly lower detection rate of H I absorption lines (~11.5%) in low-power radio AGNs with $\mathrm{log}({P}_{1.4\mathrm{GHz}}/{\rm{W}}\,{\mathrm{Hz}}^{-1})=21.8\mbox{--}23.7$ . The low-power sources with $\mathrm{log}({P}_{1.4\mathrm{GHz}}/{\rm{W}}\,{\mathrm{Hz}}^{-1})\lt 23$ have a lower detection rate of ~6.7%. Due to the incompleteness of the sample, these detection rates may represent the lower limits. The selection of more extended sources and dilution by H I emission at lower redshifts may contribute to the lower detection rate of H I absorption lines. These detected absorbers present relatively narrow line widths and comparable column densities consistent with previous observations. One absorber has a symmetric profile with a large velocity offset, while the other two show asymmetric profiles that can be decomposed into multiple components, suggesting various possibilities of gas origins and kinematics. These H I absorbers may have connections with rotating disks, gas outflows, galactic gas clouds, gas fueling of the AGN, and jet-ISM interactions, which will be further investigated with the upcoming systematic survey and spatially resolved observations.

Keywords: active galactic nuclei; radio spectroscopy; neutral hydrogen clouds
Testing Comptonization as the Origin of the Continuum in Nonmagnetic Cataclysmic Variables: The Photon Index of X-Ray Emission

The X-ray spectra of nonmagnetic cataclysmic variables (nmCVs) in the ∼0.3-15 keV energy band have been described by either one or several optically thin thermal plasma components or by cooling flow models. We tested whether the spectral continuum in nmCVs could be successfully described by Comptonization of soft photons off hot electrons presented in a cloud surrounding the source (the transition layer (TL)). We used public XMM-Newton EPIC-pn, Chandra HETG/ACIS and LETG/HRC, and RXTE PCA and HEXTE observations of four dwarf novae (U Gem, SS Cyg, VW Hyi, and SS Aur) observed in the quiescent and outburst states. In total, we analyzed 18 observations, including a simultaneous 0.4-150 keV Chandra/RXTE spectrum of SS Cyg in quiescence. We fitted the spectral continuum with up to two thermal Comptonization components (the COMPTT or COMPTB models in XSPEC) using only one thermal plasma temperature and one optical depth. In this framework, the two seed photon components are presumably coming from the innermost and outer parts of the TL (or innermost part of the disk). We obtained that the thermal Comptonization can successfully describe the spectral continuum of these nmCVs in the ∼0.4-150 keV energy band. Moreover, we present the first principal radiative transfer model that explains the quasi-constancy of the spectral photon index observed around 1.8, which strongly supports the Comptonization framework in nmCVs.

Keywords: x-ray binary stars
Measuring the Vortex-Nucleus Pinning Force from Pulsar Glitch Rates

Superfluid vortex avalanches are one plausible cause of pulsar glitch activity. If they occur according to a state-dependent Poisson process, the measured long-term glitch rate is determined by the spin-down rate of the stellar crust, ${\dot{{\rm{\Omega }}}}_{c}$ , and two phenomenological parameters quantifying the vortex-nucleus pinning force: a crust-superfluid angular velocity lag threshold, X cr, and a reference unpinning rate, λ 0. A Bayesian analysis of 541 glitches in 177 pulsars, with N g ≥ 1 events per pulsar, yields ${X}_{\mathrm{cr}}={0.15}_{-0.04}^{+0.09}\,\mathrm{rad}\,{{\rm{s}}}^{-1}$ , ${\lambda }_{\mathrm{ref}}={7.6}_{-2.6}^{+3.7}\times {10}^{-8}\,{{\rm{s}}}^{-1}$ , and $a=-{0.27}_{-0.03}^{+0.04}$ assuming the phenomenological rate law λ 0 = λ ref[τ/(1 yr)] a , where τ denotes the characteristic spin-down age. The results are broadly similar, whether one includes or excludes quasiperiodic glitch activity, giant glitches, or pulsars with N g = 0, up to uncertainties about the completeness of the sample and the total observation time per pulsar. The X cr and λ 0 estimates are consistent with first-principles calculations based on nuclear theory, e.g., in the semiclassical local density approximation.

Keywords: pulsars; neutron stars; stellar rotation; nuclear astrophysics
Generation of High-frequency Whistler Waves in the Earth's Quasi-perpendicular Bow Shock

We use observations from the Magnetospheric Multiscale spacecraft to identify a free energy source for high-frequency whistler waves in the Earth's quasi-perpendicular bow shock. In the considered measurements, whistlers propagate both parallel and antiparallel to the background magnetic field B0 with frequencies around 100 Hz (0.15 fce, where fce is the electron cyclotron frequency) and amplitudes between 0.1 and 1 nT. Their growth can be attributed to localized pitch angle anisotropy in the electron velocity distribution function that cannot be precisely described by macroscopic parameters like heat flux or temperature anisotropy. However, the presence of heat flux along -B0 does create preferential conditions for the high-frequency whistler waves that propagate in this direction. These waves are directed partially toward the shock, meaning they can scatter electrons that are streaming from the shock. This prolongs the time the electrons spend in the shock transition region and thereby promotes electron energization.

Keywords: shocks
An Old Stellar Population or Diffuse Nebular Continuum Emission Discovered in Green Pea Galaxies

We use new Hubble Space Telescope (HST) images of nine Green Pea galaxies (GPGs) to study their resolved structure and color. The choice of filters, F555W and F850LP, together with the redshift of the galaxies (z ∼ 0.25), minimizes the contribution of the nebular [O III] and Hα emission lines to the broadband images. While these galaxies are typically very blue in color, our analysis reveals that it is only the dominant stellar clusters that are blue. Each GPG does clearly show the presence of at least one bright and compact star-forming region, but these are invariably superimposed on a more extended and lower surface brightness emission. Moreover, the colors of the star-forming regions are on average bluer than those of the diffuse emission, reaching up to 0.6 magnitudes bluer. Assuming that the diffuse and compact components have constant and single-burst star formation histories, respectively, the observed colors imply that the diffuse components (possibly the host galaxy of the star formation episode) have, on average, old stellar ages (>1 Gyr), while the star clusters are younger than 500 Myr. While a redder stellar component is perhaps the most plausible explanation for these results, the limitations of our current data set lead us to examine possible alternative mechanisms, particularly recombination emission processes, which are unusually prominent in systems with such strong line emission. With the available data, however, it is not possible to distinguish between these two interpretations. A substantial presence of old stars would indicate that the mechanisms allowing large escape fractions in these local galaxies may be different from those at play during the reionization epoch.

Keywords: compact dwarf galaxies
Size Distribution of Small Jupiter Trojans in the L5 Swarm

We present an analysis of survey observations of the trailing L5 Jupiter Trojan swarm using the wide-field Hyper Suprime-Cam CCD camera on the 8.2 m Subaru Telescope. We detected 189 L5 Trojans from our survey that covered about 15 deg2 of sky with a detection limit of m r = 24.1 mag, and selected an unbiased sample consisting of 87 objects with absolute magnitude 14 ≲ H r ≤ 17 corresponding to diameter 2 km ≲ D ≲ 10 km for analysis of size distribution. We fit their differential magnitude distribution to a single-slope power law with an index α = 0.37 ± 0.01, which corresponds to a cumulative size distribution with an index of b = 1.85 ± 0.05. Combining our results with data for known asteroids, we obtained the size distribution of L5 Jupiter Trojans over the entire size range for 9 ≲ H V ≤ 17, and found that the size distributions of the L4 and L5 swarms agree well with each other for a wide range of sizes. This is consistent with the scenario that asteroids in the two swarms originated from the same primordial population. Based on the above results, the ratio of the total number of asteroids with D ≥ 2 km in the two swarms is estimated to be N L4/N L5 = 1.40 ± 0.15, and the total number of L5 Jupiter Trojans with D ≥ 1 km is estimated to be 1.1 × 105 by extrapolating the obtained distribution. *This research is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical and natural significance in Hawaii.

Keywords: jupiter trojans; trojan asteroids; optical observation; small solar system bodies; solar system formation
Temporal Evolution of Titan's Stratospheric Temperatures and Trace Gases from a Two-dimensional Retrieval of Cassini Composite Infrared Spectrometer Data

We use a two-dimensional (2D) radiative transfer model of Titan, which allows the atmospheric structure to vary in both altitude and latitude, to retrieve the spatial distribution of temperature, haze extinction, and C2H2, C2H6, C3H8, CH3C2H, C4H2, and HCN gases, from Cassini Composite Infrared Spectrometer (CIRS) limb-mapping observations over the duration of the Cassini mission. We compare our results with previous analyses of CIRS limb observations using radiative models that only allow the atmosphere to vary in altitude. The temperature, haze, and gas composition retrieved with the 2D model mostly show the same broad spatial and temporal trends as previously published results from 1D models. However, there are some significant differences in the retrieved structure at the fall and winter poles poleward of 60°. Most noticeably, the HCN abundance in the depleted region near 65°N at 350 km in northern winter is stronger in the 2D retrievals than in previous 1D retrievals, and the 2D retrievals show very different structure from earlier 1D retrievals in the north polar C2H2 structure during early northern spring, with a strong depletion around 70°N at 0.02 mbar.

Keywords: titan; natural satellite atmospheres; atmospheric structure; atmospheric composition