Sazuna/UAT_keywords huggingface dataset:
Requirements for Gravitational Collapse in Planetesimal Formation—The Impact of Scales Set by Kelvin-Helmholtz and Nonlinear Streaming Instability. The formation of planetesimals is a challenging problem in planet formation theory. A prominent scenario for overcoming dust growth barriers is the gravitational collapse of locally over-dense regions, shown to robustly produce ∼100 km-sized objects. Still, the conditions under which planetesimal formation occurs remain unclear. For collapse to proceed, the self-gravity of an over-density must overcome stellar tidal disruption on large scales and turbulent diffusion on small scales. Here, we relate the scales of streaming and Kelvin-Helmholtz instability (KHI), which both regulate particle densities on the scales of gravitational collapse, directly to planetesimal formation. We support our analytic findings by performing 3D hydrodynamical simulations of streaming and KHI and planetesimal formation. We find that the vertical extent of the particle mid-plane layer and the radial width of streaming instability filaments are set by the same characteristic length scale, thus governing the strength of turbulent diffusion on the scales of planetesimal formation. We present and successfully test a collapse criterion, 0.1Q β ɛ-1Z-1 ≲ 1, and show that even for solar metallicities, planetesimals can form in dead zones of sufficiently massive disks. For a given gas Toomre parameter Q, pressure gradient β, metallicity Z, and local particle enhancement ɛ, the collapse criterion also provides a range of unstable scales, instituting a promising path for studying initial planetesimal mass distributions. Streaming instability is not required for planetesimal collapse but, by increasing ɛ, can evolve a system to instability.

Keywords: Astrophysical fluid dynamics, Protoplanetary disks, Planet formation, Planetesimals
Barred Galaxies in the Illustris-1 and TNG100 Simulations: A Comparison Study. We carry out a comparison study on the bar structure in the Illustris-1 and TNG100 simulations. At z = 0, 8.9% of 1232 disk galaxies with stellar masses $\gt {10}^{10.5}{M}_{\odot }$ in Illustris-1 are barred, while the numbers are 55% of 1269 in TNG100. The bar fraction as a function of stellar mass in TNG100 agrees well with the survey ${S}^{4}G$ . The median redshifts of bar formation are ∼0.4-0.5 and ∼0.25 in TNG100 and Illustris-1, respectively. Bar fraction generally increases with stellar mass and decreases with gas fraction in both simulations. For galaxies with bars at z = 0, their bar formation time is generally anti-correlated with their gas fraction at high redshift. When the bars were formed, the disk gas fractions were mostly lower than 0.4. The much higher bar fraction in TNG100 probably benefits from the much lower gas fractions in massive disk galaxies since z ∼ 3, which may result from the combination of more effective stellar and AGN feedback. The latter may be the primary factor at z &lt; 2. Meanwhile, in both simulations, barred galaxies have higher star formation rates before bar formation and have stronger AGN feedback, at all times, than unbarred galaxies. The properties of dark matter halos hosting massive disk galaxies are similar between the two simulations and should have a minor effect on the frequencies of different bars. For individual galaxies under similar halo environments across the two simulations, different baryonic physics can lead to striking discrepancies in morphology. The morphologies of individual galaxies are subject to the combined effects of environment and internal baryonic physics and are often not predictable.

Keywords: Galaxy dark matter halos, Hydrodynamical simulations, Galaxy structure, Galaxy evolution, Barred spiral galaxies
Quasar Microlensing Variability Studies Favor Shallow Accretion Disk Temperature Profiles. We compare the microlensing-based continuum emission region size measurements in a sample of 15 gravitationally lensed quasars with estimates of luminosity-based thin disk sizes to constrain the temperature profile of the quasar continuum accretion region. If we adopt the standard thin disk model, we find a significant discrepancy between sizes estimated using the luminosity and those measured by microlensing of log(rL/rμ) = -0.57 ± 0.08 dex. If quasar continuum sources are simple, optically thick accretion disks with a generalized temperature profile $T(r)\propto {r}^{-\beta }$ , the discrepancy between the microlensing measurements and the luminosity-based size estimates can be resolved by a temperature profile slope 0.37 &lt; β &lt; 0.56 at 1σ confidence. This is shallower than the standard thin disk model (β = 0.75) at 3σ significance. We consider alternate accretion disk models that could produce such a temperature profile and reproduce the empirical continuum size scaling with black hole mass, including disk winds or disks with nonblackbody atmospheres.

Keywords: Accretion, Gravitational lensing, Stellar mass black holes, Quasars
The Bright Reverse Shock Emission in the Optical Afterglows of Gamma-Ray Bursts in a Stratified Medium. The reverse shock (RS) model is generally introduced to interpret the optical afterglows with the rapid rising and decaying, such as the early optical afterglow of GRB 990123 (which is also called the optical flash). In this paper, we collected 11 gamma-ray burst (GRB) early optical afterglows, which have signatures of dominant RS emission. Since the temporal slopes of the optical flashes are determined by both the medium density distribution index k and the electron spectral index p, we apply the RS model of the thin shell case to the optical flashes and determine the ambient medium of the progenitors. We find that the k value is in the range of 0-1.5. The k value in this paper is consistent with the result in Yi et al., where the forward shock model was applied to some onset bumps. However, the method adopted in this paper is only applicable to GRB afterglows with significant sharp rising and decaying RS emission. Our results indicate that the RS model can also be applied to confirm the circumburst medium, further implying that GRBs may have diverse circumburst media.

Keywords: Gamma-ray bursts, Non-thermal radiation sources
Separating Accretion and Mergers in the Cosmic Growth of Black Holes with X-Ray and Gravitational-wave Observations. Black holes across a broad range of masses play a key role in the evolution of galaxies. The initial seeds of black holes formed at z ∼ 30 and grew over cosmic time by gas accretion and mergers. Using observational data for quasars and theoretical models for the hierarchical assembly of dark matter halos, we study the relative importance of gas accretion and mergers for black hole growth, as a function of redshift (0 &lt; z &lt; 10) and black hole mass ( ${10}^{3}\,{M}_{\odot }\lt {M}_{\bullet }\lt {10}^{10}\,{M}_{\odot }$ ). We find that (I) growth by accretion is dominant in a large fraction of the parameter space, especially at ${M}_{\bullet }\gt {10}^{8}\,{M}_{\odot }$ and z &gt; 6; and (II) growth by mergers is dominant at ${M}_{\bullet }\lt {10}^{5}\,{M}_{\odot }$ and z &gt; 5.5, and at ${M}_{\bullet }\gt {10}^{8}\,{M}_{\odot }$ and z &lt; 2. As the growth channel has direct implications for the black hole spin (with gas accretion leading to higher spin values), we test our model against ∼20 robust spin measurements available thus far. As expected, the spin tends to decline toward the merger-dominated regime, thereby supporting our model. The next generation of X-ray and gravitational-wave observatories (e.g., Lynx, AXIS, Athena, and LISA) will map out populations of black holes up to very high redshift (z ∼ 20), covering the parameter space investigated here in almost its entirety. Their data will be instrumental to providing a clear picture of how black holes grew across cosmic time.

Keywords: Black hole physics, Early universe, Black holes, Galaxy evolution, Gravitational waves
A Deep CFHT Optical Search for a Counterpart to the Possible Neutron Star-Black Hole Merger GW190814. We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star-black hole (NS-BH) merger GW190814/S190814bv. This compact binary merger was detected through gravitational waves by the LIGO/Virgo interferometers, with masses suggestive of an NS-BH merger. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the Canada-France-Hawaii Telescope (CFHT). We describe our hybrid observing strategy of both tiling and galaxy-targeted observations, as well as our image differencing and transient detection pipeline. Our observing campaign produced some of the deepest multiband images of the region between 1.7 and 8.7 days post-merger, reaching a 5σ depth of g &gt; 22.8 (AB mag) at 1.7 days and I &gt; 23.1 and I &gt; 23.9 at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 67.0% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that the lighter object was tidally disrupted inside of the BH's innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object is a low-mass BH. We use 5σ source detection upper limits from our images in the NS-BH interpretation of this merger to constrain the mass of the kilonova ejecta to be Mej ≲ 0. 015M⊙ for a "blue" ( $\kappa =0.5\,{\mathrm{cm}}^{2}\ {{\rm{g}}}^{-1}$ ) kilonova and Mej ≲ 0. 04M⊙ for a "red" ( $\kappa =5\mbox{--}10\,{\mathrm{cm}}^{2}\ {{\rm{g}}}^{-1}$ ) kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational-wave events.

Keywords: Neutron stars, Gravitational waves, Black holes
The Chemistry of Cosmic Dust Analogs from C, C<SUB>2</SUB>, and C<SUB>2</SUB>H<SUB>2</SUB> in C-rich Circumstellar Envelopes. Interstellar carbonaceous dust is mainly formed in the innermost regions of circumstellar envelopes around carbon-rich asymptotic giant branch stars (AGBs). In these highly chemically stratified regions, atomic and diatomic carbon, along with acetylene, are the most abundant species after H2 and CO. In a previous study, we addressed the chemistry of carbon (C and C2) with H2 showing that acetylene and aliphatic species form efficiently in the dust formation region of carbon-rich AGBs whereas aromatics do not. Still, acetylene is known to be a key ingredient in the formation of linear polyacetylenic chains, benzene, and polycyclic aromatic hydrocarbons (PAHs), as shown by previous experiments. However, these experiments have not considered the chemistry of carbon (C and C2) with C2H2. In this work, by employing a sufficient amount of acetylene, we investigate its gas-phase interaction with atomic and diatomic carbon. We show that the chemistry involved produces linear polyacetylenic chains, benzene, and other PAHs, which are observed with high abundances in the early evolutionary phase of planetary nebulae. More importantly, we have found a nonnegligible amount of pure and hydrogenated carbon clusters as well as aromatics with aliphatic substitutions, both being a direct consequence of the addition of atomic carbon. The incorporation of alkyl substituents into aromatics can be rationalized by a mechanism involving hydrogen abstraction followed by methyl addition. All the species detected in the gas phase are incorporated into nanometric-sized dust analogs, which consist of a complex mixture of sp, sp2, and sp3 hydrocarbons with amorphous morphology.

Keywords: Asymptotic giant branch, Plasma physics, Protoplanetary nebulae, Laboratory astrophysics, Post-asymptotic giant branch, Circumstellar matter, Molecular physics, Circumstellar dust
Wandering Massive Black Holes or Analogs of the First Repeating Fast Radio Burst?. The discovery of a persistent radio source coincident with the first repeating fast radio burst, FRB 121102, and offset from the center of its dwarf host galaxy has been used as evidence for a link with young millisecond magnetars born in superluminous supernovae or long-duration gamma-ray bursts (LGRBs). A prediction of this scenario is that compact radio sources offset from the centers of dwarf galaxies may serve as signposts for at least some FRBs. Recently, Reines et al. presented the discovery of 20 such radio sources in nearby (z ≲ 0.055) dwarf galaxies, and argued that these cannot be explained by emission from H II regions, normal supernova remnants, or normal radio supernovae. Instead, they attribute the emission to accreting wandering massive black holes. Here, we explore the alternative possibility that these sources are analogs of FRB 121102. We compare their properties—radio luminosities, spectral energy distributions, light curves, ratios of radio-to-optical flux, and spatial offsets—to FRB 121102, a few other well-localized FRBs, and potentially related systems, and find that these are all consistent as arising from the same population. We further compare their properties to the magnetar nebula model used to explain FRB 121102, as well as to theoretical off-axis LGRB light curves, and find overall consistency. Finally, we find a consistent occurrence rate relative to repeating FRBs and LGRBs. We outline key follow-up observations to further test these possible connections.

Keywords: Gamma-ray bursts, Extragalactic radio sources, Dwarf galaxies, Supernova remnants, Active galactic nuclei, Magnetars, Radio transient sources
Gap-type Particle Acceleration in the Magnetospheres of Rotating Supermassive Black Holes. The detection of rapidly variable gamma-ray emission in active galactic nuclei has generated renewed interest in magnetospheric particle acceleration and emission scenarios. In order to explore its potential, we study the possibility of steady gap acceleration around the null surface of a rotating black hole magnetosphere. We employ a simplified (1D) description along with the general relativistic expression of Gauss's law, and we assume that the gap is embedded in the radiation field of a radiatively inefficient accretion flow. The model is used to derive expressions for the radial distribution of the parallel electric field component, the electron and positron charge density, the particle Lorentz factor, and the number density of γ-ray photons. We integrate the set of equations numerically, imposing suitable boundary conditions. The results show that the existence of a steady gap solution for a relative high value of the global current is in principle possible if charge injection of both species is allowed at the boundaries. We present gap solutions for different choices of the global current and the accretion rate. When put in context, our results suggest that the variable very-high-energy γ-ray emission in M87 could be compatible with a magnetospheric origin.

Keywords: Active galaxies, Rotating black holes, Gamma-rays, Particle astrophysics
Star Formation in Massive Galaxies at Redshift z ∼ 0.5. It is believed that massive galaxies have quenched their star formation because of active galactic nucleus feedback. However, recent studies have shown that some massive galaxies are still forming stars. We analyze the morphology of star formation regions for galaxies of stellar masses larger than 1011.3 M☉ at around redshift zr = 0.5 using u - z color images. We find that about 20% of the massive galaxies are star-forming (SF) galaxies, and most of them (∼85%) have asymmetric structures induced by recent mergers. Moreover, for these asymmetric galaxies, we find that the asymmetry of the SF regions becomes larger for bluer galaxies. Using the Illustris simulation, we can qualitatively reproduce the observed relation between asymmetry parameter and color. Furthermore, using the merger trees in the simulation, we find a correlation between the color of the main branch galaxies at zr = 0.5 and the sum of the star formation rates of the recently accreted galaxies, which implies that star formation of the accreted galaxies has contributed to the observed star formation of the massive (host) galaxies (ex situ star formation). Furthermore, we find two blue and symmetric galaxies, candidates for massive blue disks, in our observed sample, which indicates that about ∼10% of massive SF galaxies are forming stars in the normal mode of disk star formation (in situ star formation). With the simulation, we find that the disk galaxies at zr ≍ 0.5 should have experienced few major mergers during the last 4.3 Gyr.

Keywords: Galaxy infall, Galaxy disks, Star formation, Galaxy mergers, Galaxy quenching
Efficient Methanol Production on the Dark Side of a Prestellar Core. We present Atacama Large Millimeter/submillimeter Array maps of the starless molecular cloud core Ophiuchus/H-MM1 in the lines of deuterated ammonia (ortho- ${\mathrm{NH}}_{2}{\rm{D}}$ ), methanol ( ${\mathrm{CH}}_{3}\mathrm{OH}$ ), and sulfur monoxide (SO). The dense core is seen in ${\mathrm{NH}}_{2}{\rm{D}}$ emission, whereas the ${\mathrm{CH}}_{3}\mathrm{OH}$ and SO distributions form a halo surrounding the core. Because methanol is formed on grain surfaces, its emission highlights regions where desorption from grains is particularly efficient. Methanol and sulfur monoxide are most abundant in a narrow zone that follows the eastern side of the core. This side is sheltered from the stronger external radiation field coming from the west. We show that photodissociation on the illuminated side can give rise to an asymmetric methanol distribution but that the stark contrast observed in H-MM1 is hard to explain without assuming enhanced desorption on the shaded side. The region of the brightest emission has a wavy structure that rolls up at one end. This is the signature of Kelvin-Helmholtz instability occurring in sheared flows. We suggest that in this zone, methanol and sulfur are released as a result of grain-grain collisions induced by shear vorticity.

Keywords: Interstellar molecules, Interstellar dust processes, Dense interstellar clouds, Astrochemistry
Correlations between Black Holes and Host Galaxies in the Illustris and IllustrisTNG Simulations. We study black hole-host galaxy correlations, and the relation between the overmassiveness (the distance from the average MBH-σ relation) of supermassive black holes (SMBHs) and the star formation histories of their host galaxies in the Illustris and TNG100 simulations. We find that both simulations are able to produce black hole scaling relations in general agreement with observations at z = 0, but with noticeable discrepancies. Both simulations show an offset from the observations for the MBH-σ relation, and the relation between MBH and the Sérsic index. The relation between MBH and stellar mass M* is tighter than the observations, especially for TNG100. For massive galaxies in both simulations, the hosts of overmassive SMBHs (those above the mean MBH-σ relation) tend to have larger Sérsic indices and lower baryon conversion efficiency, suggesting a multidimensional link between SMBHs and the properties of their hosts. In Illustris, the hosts of overmassive SMBHs have formed earlier and have lower present-day star formation rates, in qualitative agreement with the observations for massive galaxies with σ &gt; 100 km s-1. For low-mass galaxies, such a correlation still holds in Illustris but does not exist in the observed data. For TNG100, the correlation between SMBH overmassiveness and star formation history is much weaker. The hosts of overmassive SMBHs generally have consistently larger star formation rates throughout history. These galaxies have higher stellar mass as well, due to the strong MBH-M* correlation. Our findings show that simulated SMBH scaling relations and correlations are sensitive to features in the modeling of SMBHs.

Keywords: Supermassive black holes, Star formation, Galaxy evolution, Galaxies
Galactic Cosmic-ray Anisotropies: Electrons Observed by Voyager 1 in the Very Local Interstellar Medium. Now over seven years into its journey beyond the heliopause, Voyager 1 continues to return unprecedented observations of energetic particles, magnetic fields, and plasma emissions from the very local interstellar medium. Shortly after its heliopause crossing, Voyager 1 discovered an unusual time-varying galactic cosmic-ray anisotropy, characterized by smoothly changing intensity reductions in particles propagating nearly perpendicular to the magnetic field; outside of this isolated region, cosmic rays appear mostly unvarying, without a significant radial gradient. These small (∼15%) but lasting (∼100 to ∼630 days) anisotropic events are still not fully understood. Nevertheless, they serve as clear markers, together with shorter-lived cosmic-ray intensity enhancements, electron plasma oscillations, and weak laminar shocks, that even beyond the heliopause, the Sun's variable output significantly influences its surroundings. So far, these unusual energetic particle occurrences have mainly been studied using integrated proton intensities of ∼20 MeV and higher. Using data from the Voyager 1 Cosmic Ray Subsystem, we extend the analysis to electrons, as well as lower energy protons, and discover the surprising new result that the ∼3 to ∼105 MeV electrons remain mostly isotropic and unchanging, in sharp contrast to their proton counterparts. We search for clues to explain this underlying species dependence and rule out potential causes related to instrumental effects, velocity and energy, trapping and energy loss, drifts, and turbulence-induced scattering. We also explore some plausible mechanisms and open the door for more detailed follow-up theories and simulations.

Keywords: Heliopause, Space plasmas, Heliosphere, Galactic cosmic rays, Collision physics, Interstellar medium, Solar activity, Particle astrophysics
SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). IV. Spatial Clustering and Halo Masses of Submillimeter Galaxies. We analyze an extremely deep 450 μm image (1σ = 0.56 mJy beam-1) of a ≃300 arcmin2 area in the CANDELS/COSMOS field as part of the Sub-millimeter Common User Bolometric Array-2 Ultra Deep Imaging EAO Survey. We select a robust (signal-to-noise ratio ≥4) and flux-limited (≥4 mJy) sample of 164 submillimeter galaxies (SMGs) at 450 μm that have K-band counterparts in the COSMOS2015 catalog identified from radio or mid-infrared imaging. Utilizing this SMG sample and the 4705 K-band-selected non-SMGs that reside within the noise level ≤1 mJy beam-1 region of the 450 μm image as a training set, we develop a machine-learning classifier using K-band magnitude and color-color pairs based on the 13-band photometry available in this field. We apply the trained machine-learning classifier to the wider COSMOS field (1.6 deg2) using the same COSMOS2015 catalog and identify a sample of 6182 SMG candidates with similar colors. The number density, radio and/or mid-infrared detection rates, redshift and stellar-mass distributions, and the stacked 450 μm fluxes of these SMG candidates, from the S2COSMOS observations of the wide field, agree with the measurements made in the much smaller CANDELS field, supporting the effectiveness of the classifier. Using this SMG candidate sample, we measure the two-point autocorrelation functions from z = 3 down to z = 0.5. We find that the SMG candidates reside in halos with masses of ≃(2.0 ± 0.5) × 1013 h-1 M⊙ across this redshift range. We do not find evidence of downsizing that has been suggested by other recent observational studies.

Keywords: Galaxy formation, Large-scale structure of the universe, Clustering, Galaxy evolution, Submillimeter astronomy, High-redshift galaxies