Sazuna/UAT_keywords huggingface dataset:
Color Gradients along the Quiescent Galaxy Sequence: Clues to Quenching and Structural Growth. This Letter examines how the sizes, structures, and color gradients of galaxies change along the quiescent sequence. Our sample consists of ∼400 quiescent galaxies at 1.0 ≤ z ≤ 2.5 and $10.1\leqslant \mathrm{log}{M}_{* }/{M}_{\odot }\leqslant 11.6$ in three CANDELS fields. We exploit deep multi-band Hubble Space Telescope imaging to derive accurate mass profiles and color gradients, then use an empirical calibration from rest-frame UVJ colors to estimate galaxy ages. We find that—contrary to previous results—the youngest quiescent galaxies are not significantly smaller than older quiescent galaxies at fixed stellar mass. These "post-starburst" galaxies only appear smaller in half-light radii because they have systematically flatter color gradients. The strength of color gradients in quiescent galaxies is a clear function of age, with older galaxies exhibiting stronger negative color gradients (i.e., redder centers). Furthermore, we find that the central mass surface density Σ1 is independent of age at fixed stellar mass, and only weakly depends on redshift. This finding implies that the central mass profiles of quiescent galaxies do not significantly change with age; however, we find that older quiescent galaxies have additional mass at large radii. Our results support the idea that building a massive core is a necessary requirement for quenching beyond z = 1, and indicate that post-starburst galaxies are the result of a rapid quenching process that requires structural change. Furthermore, our observed color gradient and mass profile evolution supports a scenario where quiescent galaxies grow inside-out via minor mergers.

Keywords: Galaxy quenching, Galaxy formation, Galaxy structure, Galaxy evolution
Implications of a Fast Radio Burst from a Galactic Magnetar. A luminous radio burst was recently detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154 with a time and frequency structure consistent with cosmological fast radio bursts (FRBs) and a fluence within a factor of ≲10 of the least energetic extragalactic FRB previously detected. Although active magnetars are commonly invoked FRB sources, several distinct mechanisms have been proposed for generating the radio emission that make different predictions for the accompanying higher-frequency radiation. We show that the properties of the coincident radio and X-ray flares from SGR 1935+2154, including their approximate simultaneity and relative fluence ${E}_{\mathrm{radio}}/{E}_{{\rm{X}}}\sim {10}^{-5}$ , as well as the duration and spectrum of the X-ray emission, are consistent with extant predictions for the synchrotron maser shock model. Rather than arising from the inner magnetosphere, the X-rays are generated by (incoherent) synchrotron radiation from thermal electrons heated at the same internal shocks that produce the coherent maser emission as ultrarelativistic flare ejecta collides with a slower particle outflow (e.g., as generated by earlier flaring activity) on a radial scale of $\sim {10}^{11}$ cm. Although the rate of SGR 1935+2154-like bursts in the local universe is not sufficient to contribute appreciably to the extragalactic FRB rate, the inclusion of an additional population of more active magnetars with stronger magnetic fields than the Galactic population can explain both the FRB rate and the repeating fraction, but only if the population of active magnetars are born at a rate that is at least 2 orders of magnitude lower than that of the SGR 1935+2154-like magnetars. This may imply that the more active magnetar sources are not younger magnetars formed in a similar way to the Milky Way population (e.g., via ordinary supernovae) but are instead formed through more exotic channels, such as superluminous supernovae, accretion-induced collapse, or neutron star mergers.

Keywords: Magnetars, Soft gamma-ray repeaters, Radio transient sources
Prebiotic Precursors of the Primordial RNA World in Space: Detection of NH<SUB>2</SUB>OH. One of the proposed scenarios for the origin of life is the primordial RNA world, which considers that RNA molecules were likely responsible for the storage of genetic information and the catalysis of biochemical reactions in primitive cells, before the advent of proteins and DNA. In the last decade, experiments in the field of prebiotic chemistry have shown that RNA nucleotides can be synthesized from relatively simple molecular precursors, most of which have been found in space. An important exception is hydroxylamine, NH2OH, which, despite several observational attempts, it has not been detected in space yet. Here we present the first detection of NH2OH in the interstellar medium toward the quiescent molecular cloud G+0.693-0.027 located in the Galactic Center. We have targeted the three groups of transitions from the J = 2-1, 3-2, and 4-3 rotational lines, detecting five transitions that are unblended or only slightly blended. The derived molecular abundance of NH2OH is (2.1 ± 0.9) × 10-10. From the comparison of the derived abundance of NH2OH and chemically related species, with those predicted by chemical models and measured in laboratory experiments, we favor the formation of NH2OH in the interstellar medium via hydrogenation of NO on dust grain surfaces, with possibly a contribution of ice-mantle NH3 oxidation processes. Further laboratory studies and quantum chemical calculations are needed to completely rule out the formation of NH2OH in the gas phase.

Keywords: Interstellar molecules, Galactic center, Astrochemistry, Astrobiology, Pre-biotic astrochemistry
Comparative Analyses of Plasma Properties and Composition in Two Types of Small-scale Interplanetary Flux-ropes. The origin of small-scale interplanetary magnetic flux-ropes (SIMFRs) and the relationship between SIMFRs and magnetic clouds (MCs) are still controversial. In this study, two populations of SMIFRs were collected, i.e., SIMFRs originating from the Sun (SIMFR-SUN) and those originating from the solar wind (SIMFR-SW). We defined the SIMFR-SUN (SIMFR-SW) as the SMIFRs that include (exclude) the counter-streaming suprathermal electrons and stay away from (close to) the heliospheric current sheet. After fitting with force-free flux-rope model, 52 SIMFR-SUN and 57 SIMFR-SW events observed by Advanced Composition Explorer from 1998 February to 2011 August were qualified. Using the approach of relating the measurements to their spatial position within the flux ropes, a comparative survey of plasma and composition characteristics inside the two populations of SIMFRs is presented. Results show that the two populations of SIMFRs have apparent differences. Compared with SIMFR-SW, SIMFR-SUN are MC-like, featuring lower central proton density, higher Vrad, higher low-FIP element abundances, higher and more fluctuate average ion charge-states and the ion charge-state ratios that are related to the heating in the low corona. In addition, for the ion charge-state distributions inside SIMFR-SUN, the sunward side is higher than earthward, which might be caused by the flare heating during eruption. Moreover, both SIMFR-SUN and MCs show anticorrelation between plasma β and the He/P trend. These characteristics indicate that SIMFR-SUN and MCs are very likely to have identical origination. This study supports the two-source origin of SIMFRs, i.e., the solar corona and the solar wind.

Keywords: Solar wind, Interplanetary physics, Solar coronal mass ejections
Winds in Star Clusters Drive Kolmogorov Turbulence. Intermediate and massive stars drive fast and powerful isotropic winds that interact with the winds of nearby stars in star clusters and the surrounding interstellar medium (ISM). Wind-ISM collisions generate astrospheres around these stars that contain hot T ∼ 107 K gas that adiabatically expands. As individual bubbles expand and collide they become unstable, potentially driving turbulence in star clusters. In this Letter we use hydrodynamic simulations to model a densely populated young star cluster within a homogeneous cloud to study stellar wind collisions with the surrounding ISM. We model a mass-segregated cluster of 20 B-type young main-sequence stars with masses ranging from 3 to 17 M⊙. We evolve the winds for ∼11 kyr and show that wind-ISM collisions and overlapping wind-blown bubbles around B-stars mix the hot gas and ISM material, generating Kolmogorov-like turbulence on small scales early in its evolution. We discuss how turbulence driven by stellar winds may impact the subsequent generation of star formation in the cluster.

Keywords: B stars, Interstellar medium, Star clusters
Electron Energization and Energy Dissipation in Microscale Electromagnetic Environments. Particle energization and energy dissipation in electromagnetic environments are longstanding topics of intensive research in space, laboratory, and astrophysical plasmas. One challenge is to understand these conversion processes at smaller and smaller spatial/temporal scales. In this Letter, with very high cadence measurements of particle distributions from the Magnetospheric Multiscale spacecraft, we report evidence of evolution of an identified microscale (i.e., electron gyro-scale) magnetic cavity structure and reveal within it a unique energization process that does not adhere to prevailing adiabatic invariance theory. Our finding indicates that this process is largely energy dependent, and can accelerate/decelerate charged particles inside the trapping region during their gyromotion, clearly altering the particle distribution.

Keywords: Space plasmas
Effects of Solar Activity on Taylor Scale and Correlation Scale in Solar Wind Magnetic Fluctuations. The correlation scale and the Taylor scale are evaluated for interplanetary magnetic field fluctuations from two-point, single time correlation function using the Advanced Composition Explorer (ACE), Wind, and Cluster spacecraft data during the time period from 2001 to 2017, which covers over an entire solar cycle. The correlation scale and the Taylor scale are respectively compared with the sunspot number to investigate the effects of solar activity on the structure of the plasma turbulence. Our studies show that the Taylor scale increases with the increasing sunspot number, which indicates that the Taylor scale is positively correlated with the energy cascade rate, and the correlation coefficient between the sunspot number and the Taylor scale is 0.92. However, these results are not consistent with the traditional knowledge in hydrodynamic dissipation theories. One possible explanation is that in the solar wind, the fluid approximation fails at the spatial scales near the dissipation ranges. Therefore, the traditional hydrodynamic turbulence theory is incomplete for describing the physical nature of the solar wind turbulence, especially at the spatial scales near the kinetic dissipation scales.

Keywords: Interplanetary medium, Space plasmas, Solar cycle, Interplanetary turbulence, Solar wind, Solar magnetic fields, Solar activity
Chromatic Microlensing Time Delays. Due to the finite size of the disk and the temperature fluctuations producing the variability, microlensing changes the actual time delays between images of strongly lensed active galactic nuclei on the ∼day(s) light-crossing timescale of the emission region. This microlensing-induced time delay depends on the disk model, primarily the disk size Rdisk, which has been found to be larger than predicted by the thin-disk model. In this work, we propose that light curves measured in different bands will give different time delays because Rdisk is a function of wavelength; by measuring the time-delay differences between bands, one can (1) directly verify such an new effect, and (2) test the thin-disk model of quasars. For the second goal, our method can avoid the potential inconsistency between multi-band light curves that may bias the results by continuum reverberation mapping. We conduct a simulation based on a PG 1115+080-like lensed quasar, calculating the theoretical distributions of time-delay differences between two bands: u and i centered around 354 nm and 780 nm, under and beyond the thin-disk model, respectively. Assuming that the disk size is twice the size of the standard one, we find that with a precision of 2 days in the time-delay difference measurements, the microlensing time delay effect can be verified with ∼4 measurements, while with ∼35 measurements the standard model can be excluded. This approach could be realized in the ongoing and upcoming multi-band wide-field surveys with follow-up observations.

Keywords: Quasar microlensing, Gravitational lensing
Monitoring the Spatio-temporal Evolution of a Reconnection X-line in Space. Inherently, magnetic reconnection—the process responsible for stellar flares and magnetospheric substorms—is very dynamic in space, owing to magnetic fluctuations and unsteady inflows. However, this process was always explained as a static picture in spacecraft measurements, neglecting the temporal evolution. This picture is not correct. Here we provide the first dynamic picture of magnetic reconnection in space, by monitoring the spatio-temporal evolution of a reconnection X-line at the magnetopause. Surprisingly, we find that the angle of a reconnection X-line can change from 44°8 to 24°9 during tens of milliseconds, which is significantly smaller than the characteristic timescale of the reconnection process (t = di/VA ∼ 410 ms). Meanwhile, the spacecraft moves from the inflow region to the outflow region (spatial evolution). This result demonstrates that the magnetic reconnection in space can develop rapidly during tens of milliseconds, and thus that the concept of dynamic reconnection should be invoked instead of a static diagram.

Keywords: Space plasmas, Solar magnetic reconnection, Plasma physics, Solar wind, Dynamical evolution
Asymmetry in the Length Scales of the Solar Supergranulation Network. Supergranulation is the horizontal velocity pattern on the solar surface with a typical size of 30,000 km and a lifetime of 24 hr. The network structure seen in chromospheric lines, such as Ca II K 3934 Å, is the manifestation of supergranulation. The network seen in the extreme-ultraviolet lines like He II 304 Å is the extension of the chromospheric network into the upper solar atmosphere. We have obtained the length scales of the supergranulation network from the autocorrelation function of calcium II K spectroheliograms from the Kodaikanal archival data. The behavior of the length scales in the horizontal (parallel to the direction of rotation) and vertical (perpendicular to the direction of rotation) have been obtained in different latitudes for a period of about 100 yr. The time-averaged length scales show a nearly symmetric variation in the northern and southern hemispheres. The length scales also show a profound asymmetry in the horizontal and vertical directions, which is dependent on solar latitude. A comparison reveals that both length scales are almost equal near the equatorial latitudes, but the vertical length scales relatively become smaller toward higher latitudes. The asymmetry is independently verified from He II 304 Å images from the Solar Dynamic Observatory/Atmospheric Imaging Assembly. As the length scales are related to the width of the network, the results point to the asymmetry in the supergranular cell boundary. Supergranulation is one of the basic length scales of solar convection, hence these results can have implications for the convection in Sun-like stars.

Keywords: Solar cycle, Solar atmosphere, Solar chromosphere
The ALPINE-ALMA [C II] Survey: Size of Individual Star-forming Galaxies at z = 4-6 and Their Extended Halo Structure. We present the physical extent of [C II] 158 μm line-emitting gas from 46 star-forming galaxies at z = 4-6 from the ALMA Large Program to INvestigate C II at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C II] line (${r}_{{\rm{e}},[{\rm{C}}{\rm\small{II}}]}$) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum (${r}_{{\rm{e}},\mathrm{UV}}$) from Hubble Space Telescope images. The effective radius ${r}_{{\rm{e}},[{\rm{C}}{\rm\small{II}}]}$ exceeds ${r}_{{\rm{e}},\mathrm{UV}}$ by factors of ∼2-3, and the ratio of ${r}_{{\rm{e}},[{\rm{C}}{\rm\small{II}}]}/{r}_{{\rm{e}},\mathrm{UV}}$ increases as a function of Mstar. We do not find strong evidence that the [C II] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ≃1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C II] component over 10 kpc scales detected at 4.1σ-10.9σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C II]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C II] line structure have high star formation rate, high stellar mass (Mstar), low Lyα equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Lyα line), as compared to galaxies without such extended [C II] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C II] line structures are ubiquitous to high-z star-forming galaxies.

Keywords: Galaxy formation, Galaxy evolution, Interstellar medium, Circumgalactic medium
Atmospheric Temperature Inversions and He I 5876 Core Profile Structure in White Dwarfs. We report distinctive core profiles in the strongest optical helium line, He I λ5876, from high-resolution high-sensitivity observations of spectral type DB white dwarfs. By analyzing a sample of 40 stars from Keck/HIRES and VLT/UVES, we find the core appearance to be related to the degree of hydrogen and heavy element content in the atmosphere. New Ca K-line measurements or upper limits are reported for about half the sample stars. He I λ5876 emission cores with a self-reversed central component are present for those stars with relatively low hydrogen abundance, as well as relatively low atmospheric heavy element pollution. This self-reversed structure disappears for stars with higher degrees of pollution and/or hydrogen abundance, giving way to a single absorption core. From our model atmospheres, we show that the self-reversed emission cores can be explained by temperature inversions in the upper atmosphere. We propose that the transition to a single absorption core is due to the additional opacity from hydrogen and heavy elements that inhibits the temperature inversions. Our current models do not exactly match the effective temperature range of the phenomenon or the amplitude of the self-reversed structure, which is possibly a result of missing physics such as 3D treatment, convective overshoot, and/or non-LTE effects. The He I λ5876 line structure may prove to be a useful new diagnostic for calibrating temperature profiles in DB atmosphere models.

Keywords: Extrasolar rocky planets, High resolution spectroscopy, Upper atmosphere, DB stars, White dwarf stars, Stellar atmospheric opacity, Stellar effective temperatures, Stellar atmospheres
Tidal Disruption Flares from Stars on Marginally Bound and Unbound Orbits. We study the mass fallback rate of tidally disrupted stars on marginally bound and unbound orbits around a supermassive black hole (SMBH) by performing three-dimensional smoothed particle hydrodynamic simulations with three key parameters. The star is modeled by a polytrope with two different indexes (n = 1.5 and 3). The stellar orbital properties are characterized by five orbital eccentricities ranging from e = 0.98 to 1.02, and five different penetration factors ranging from β = 1 to 3, where β represents the ratio of the tidal disruption to pericenter distance radii. We derive analytic formulae for the mass fallback rate as a function of the stellar density profile, orbital eccentricity, and penetration factor. Moreover, two critical eccentricities to classify tidal disruption events (TDEs) into five different types: eccentric ($e\lt {e}_{\mathrm{crit},1}$), marginally eccentric (${e}_{\mathrm{crit},1}\lesssim e\lt 1$), purely parabolic (e = 1), marginally hyperbolic ($1\lt e\lt {e}_{\mathrm{crit},2}$), and hyperbolic ($e\gtrsim {e}_{\mathrm{crit},2}$) TDEs, are reevaluated as ${e}_{\mathrm{crit},1}=1-2{q}^{-1/3}{\beta }^{k-1}$ and ${e}_{\mathrm{crit},2}=1+2{q}^{-1/3}{\beta }^{k-1}$, where q is the ratio of the SMBH to stellar masses and 0 &lt; k ≲ 2. We find the asymptotic slope of the mass fallback rate varies with the TDE type. The asymptotic slope approaches -5/3 for the parabolic TDEs, is steeper for the marginally eccentric TDEs, and is flatter for the marginally hyperbolic TDEs. For the marginally eccentric TDEs, the peak of mass fallback rates can be about one order of magnitude larger than the parabolic TDE case. For marginally hyperbolic TDEs, the mass fallback rates can be much lower than the Eddington accretion rate, which can lead to the formation of a radiatively inefficient accretion flow, while hyperbolic TDEs lead to failed TDEs. Marginally unbound TDEs could be an origin of a very low-density gas disk around a dormant SMBH.

Keywords: Accretion, Black hole physics, Tidal disruption, Galaxy nuclei
The Age Distribution of Stars in the Milky Way Bulge. The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125,367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (APOGEE) DR14. We examine the ages and metallicities of 1654 bulge stars within ${R}_{\mathrm{GAL}}\lt 3.5\,\mathrm{kpc}$. We focus on fields with b &lt; 12°, and out to longitudes of l &lt; 15°. We see that stars in the bulge are about twice as old (τ = 8 Gyr), on average, compared to those in the solar neighborhood (τ = 4 Gyr), with a larger dispersion in [Fe/H] (≈0.38 compared to 0.23 dex). This age gradient comes primarily from the low-α stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] (σ[Fe/H] ≈ 0.4 dex) and line-of-sight velocity (σvr ≈ 90 km s-1), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of b = 8°, but not at b = 12°. Future APOGEE and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.

Keywords: Stellar properties, Stellar ages, Stellar abundances, Galactic bulge, Milky Way Galaxy