adsabs/SciX_UAT_keywords huggingface dataset:
Effects of the Compressibility of Turbulence on the Dust Coagulation Process in Protoplanetary Disks

Planetesimals are believed to be formed by the coagulation of dust grains in the protoplanetary disk turbulence. However, the bouncing and fragmentation barriers have not been completely solved, particularly for silicate dust. To circumvent these barriers, the turbulent clustering of dust particles must be properly treated. According to the minimum-mass solar nebula (MMSN) model, the Mach number of the turbulence ranges from Mrms ≃ 0.01-0.32, and thus the turbulence is often regarded as essentially incompressible. However, it has not been quantitatively investigated whether the incompressible limit is adequate for protoplanetary disk simulations. We therefore compare in this study the motions of inertial particles in direct numerical simulations (DNSs) of the Navier-Stokes equation between weakly compressible turbulence and incompressible turbulence. In the DNSs of compressible turbulence, we use an external force to set the total dissipation and the dilatational-to-solenoidal dissipation ratio. The DNSs reveal that despite the small Mach number Mrms( ≲ 0.3), the compressible turbulence field notably differs from the incompressible field in terms of the density fluctuations, pressure fluctuations, and shocklet generation, depending on the ratio of the dilatational forcing. However, we quantitatively confirmed that these effects on the particle collision statistics are weak and that the motion of inertial particles in weakly compressible turbulence is dominated by the solenoidal velocity components. Therefore we can conclude that the incompressible assumption is appropriate for an investigation of the dust coagulation process in protoplanetary disk turbulence, as assumed in the MMSN model.

Keywords: planetesimals; protoplanetary disks; planet formation; interplanetary turbulence; astrophysical fluid dynamics; hydrodynamics; hydrodynamical simulations
The Obscured Fraction of Quasars at Cosmic Noon

Statistical studies of X-ray selected active galactic nuclei (AGN) indicate that the fraction of obscured AGN increases with increasing redshift, and the results suggest that a significant part of the accretion growth occurs behind obscuring material in the early universe. We investigate the obscured fraction of highly accreting X-ray AGN at around the peak epoch of supermassive black hole growth utilizing the wide and deep X-ray and optical/IR imaging data sets. A unique sample of luminous X-ray selected AGNs above z > 2 was constructed by matching the XMM-SERVS X-ray point-source catalog with a point-spread function convolved photometric catalog covering the u*-4.5 μm bands. Photometric redshift, hydrogen column density, and 2-10 keV AGN luminosity of the X-ray selected AGN candidates were estimated. Using the sample of 306 2-10 keV detected AGN at above redshift 2, we estimate the fraction of AGN with $\mathrm{log}{N}_{{\rm{H}}}\ ({\mathrm{cm}}^{-2})\gt 22$ , assuming parametric X-ray luminosity and absorption functions. The results suggest that ${76}_{-3}^{+4} \% $ of luminous quasars ( $\mathrm{log}{L}_{X}\ (\mathrm{erg}\ {{\rm{s}}}^{-1})\gt 44.5$ ) above redshift 2 are obscured. The fraction indicates an increased contribution of obscured accretion at high redshift than that in the local universe. We discuss the implications of the increasing obscured fraction with increasing redshift based on the AGN obscuration scenarios, which describe obscuration properties in the local universe. Both the obscured and unobscured z > 2 AGN show a broad range of SEDs and morphology, which may reflect the broad variety of host galaxy properties and physical processes associated with the obscuration.

Keywords: active galactic nuclei; supermassive black holes; quasars
Molecular Gas in a Gravitationally Lensed Galaxy Group at z = 2.9

Most molecular gas studies of z > 2.5 galaxies are of intrinsically bright objects, despite the galaxy population being primarily normal galaxies with less extreme star formation rates. Observations of normal galaxies at high redshift provide a more representative view of galaxy evolution and star formation, but such observations are challenging to obtain. In this work, we present Atacama Large Millimeter/submillimeter Array 12CO(J = 3 → 2) observations of a submillimeter selected galaxy group at z = 2.9, resulting in spectroscopic confirmation of seven images from four member galaxies. These galaxies are strongly lensed by the MS 0451.6-0305 foreground cluster at z = 0.55, allowing us to probe the molecular gas content on levels of 109-1010 M⊙. Four detected galaxies have molecular gas masses of (0.2-13.1) × 1010 M⊙, and the nondetected galaxies have inferred molecular gas masses of <8.0 × 1010 M⊙. We compare these new data to a compilation of 546 galaxies up to z = 5.3, and find that depletion times decrease with increasing redshift. We then compare the depletion times of galaxies in overdense environments to the field-scaling relation from the literature, and find that the depletion time evolution is steeper for galaxies in overdense environments than for those in the field. More molecular gas measurements of normal galaxies in overdense environments at higher redshifts (z > 2.5) are needed to verify the environmental dependence of star formation and gas depletion.

Keywords: galaxy evolution; high-redshift galaxies; high-redshift galaxy clusters; star formation; strong gravitational lensing
The Central 300 pc of the Galaxy Probed by Infrared Spectra of H3 + and CO. III. Locations of Sgr B2 and Star Iota

Using a simple relation between the radial expansion velocity of diffuse gas in the Central Molecular Zone (CMZ) of the Galaxy and its distance from Sgr A* we estimate the physical depths within the CMZ of Star ι (2MASS J17470898-2829561) and two Sgr B2 far-infrared continuum sources with respect to the location of Sgr A*. To do this we use velocity profiles of infrared absorption lines of ${{\rm{H}}}_{3}^{+}$ and of far-infrared absorption lines of H2O+, OH+, and 13CH+. The distances to Star ι and to the Sgr B2 sources are found to be ~90 pc greater than the distance to Sgr A*. Our conclusion that Sgr B2 lies toward the rear of the CMZ is contrary to most previous models in which it has been placed shallower than Sgr A*.

Keywords: astrochemistry; galactic center; high energy astrophysics; interstellar line absorption; interstellar molecules
Clump-scale Gas Infall in High-mass Star Formation: A Multitransition View with James Clerk Maxwell Telescope HCN (4-3) Mapping

Gas infall motions play a crucial role in high-mass star formation and are characterized by observable signatures of blueshifted asymmetric spectral line profiles ("blue profiles"). However, the connection between blue profiles and infall motions is unclear due to complex gas motions at parsec scales. In this study, we present the results of an HCN (4-3) mapping survey conducted with the James Clerk Maxwell Telescope, toward 38 massive clumps exhibiting blue profiles in HCO+ (3-2). We extract 34 HCN cores from the 38 observed fields. The core-averaged spectra show various line profiles, indicating that blue-profile HCO+ (3-2) does not guarantee the same in HCN (4-3). Through non-LTE radiative-transfer calculations, we attribute the low detection rate of high-J blue profiles to a combination of insufficient HCN (4-3) opacity and the intricate gas motion across different density layers. A comparison between the MALT90 and Bolocam Galactic Plane Survey line surveys highlights the importance of appropriate tracers, high spectral resolution, and column density thresholds when searching for blue profiles. We select 11 reliable infall candidates and adopt the Hill5 model to fit the infall velocity of 0.2-1.6 km s-1, corresponding to 5%-74% of freefall velocity. Assuming a spherically collapsing model, we estimate the median and mean mass infall rates to be 4.5 × 10-3 and 7.6 × 10-3 M ⊙ yr-1, respectively. The consistency of the mass infall rates among different transitions suggests a steady accretion process from the clump gas envelope to the inner region.

Keywords: star formation; interstellar dynamics
Broadband Variability Study of Maxi J1631-479 in Its Hard-intermediate State Observed with Insight-HXMT

We report the energy-resolved broadband timing analysis of the black hole X-ray transient MAXI J1631-479 during its 2019 outburst from February 11 to April 9, using data from the Insight-Hard X-ray Modulation Telescope (Insight-HXMT), which caught the source from its hard-intermediate state to the soft state. Thanks to the large effective area of Insight-HXMT at high energies, we are able to present the energy dependence of fast variability up to ~100 keV. Type-C quasi-periodic oscillations (QPOs) with a frequency varying between 4.9 and 6.5 Hz are observed in the 1-100 keV energy band. While the QPO fractional rms increases with photon energy from 1 keV to ~10 keV and remains more or less constant from ~10 keV to ~100 keV, the rms of the flat-top noise first increases from 1 keV to ~8 keV and then drops to less than 0.1% above ~30 keV. We suggest that the disappearance of the broadband variability above 30 keV could be caused by the nonthermal acceleration in the Comptonizing plasma. At the same time, the QPOs could be produced by the precession of either a small-scale jet or a hot inner flow model.

Keywords: stellar accretion disks; low-mass x-ray binary stars; black hole physics
Reclassifying Swift Gamma-Ray Bursts with Diverse Duration Distributions

We select the largest sample of Swift gamma-ray bursts (GRBs) so far to reexamine the classification in terms of time duration, hardness ratio, and physical collapse model. To analyze the sample selection effect, we divide the observed Swift GRB sample into four subsamples according to signal-to-noise level, spectral quality, and extended emission. First, we find that only the sample of Swift GRBs with well-measured peak energy can be evidently divided into two types at a boundary of ~1 s, and other data sets are well described by three Gaussian functions. Using Swift GRBs with known redshift, a Kolmogorov-Smirnov test shows the intrinsic duration distributions of five data sets are equally distributed. Second, we ascertain in the plane of hardness ratio versus duration that the hardness ratio of short GRBs is significantly higher than those of middle classes and long GRBs, while the latter two components are the same in statistics, implying the so-called middle class to be artificial. Third, we apply a collapse model to discriminate the boundaries between collapse and noncollapse Swift bursts. It is interesting to find that a significant fraction, ≥30%, of Swift short GRBs could have originated from the collapsing progenitors, while all long GRBs are produced from the collapsars only. Finally, we point out that short GRBs with extended emission are the main contributors to the noncollapsar population with longer duration.

Keywords: gamma-ray bursts
MiMO: Mixture Model for Open Clusters in Color-Magnitude Diagrams

We propose a mixture model of open clusters (OCs) in color-magnitude diagrams (CMDs) to measure the OC properties, including isochrone parameters (age, distance, metallicity, and dust extinction), stellar mass function (MF), and binary parameters (binary fraction and mass-ratio distribution), with high precision and reliability. The model treats an OC in the CMD as a mixture of single and binary member stars and field stars in the same region. The cluster members are modeled using a theoretical stellar model, mass function, and binary properties. The field component is modeled nonparametrically using a separate field-star sample in the vicinity of the cluster. Unlike conventional methods that rely on stringent member selection, ours allows us to use a sample of more complete cluster members and attendant field stars. The larger star sample reduces the statistical error and diminishes the potential bias by retaining more stars that are crucial for age estimation and MF measurement. After validating the method with 1000 mock clusters, we measured the parameters of 10 real OCs using Gaia EDR3 data. The best-fit isochrones are consistent with previous measurements in general but with more precise age estimates for several OCs. The inferred MF slope is -2.7 to -1.6 for clusters younger than 2 Gyr, while older clusters appear to have significantly flatter MFs. The binary fraction is 30%-50%. The photometric and astrometric distances agree well.

Keywords: open star clusters; binary stars; stellar mass functions; stellar ages; hertzsprung russell diagram; mixture model; bayesian statistics
Anisotropies in Compressible MHD Turbulence: Probing Magnetic Fields and Measuring Magnetization

Probing magnetic fields in the interstellar medium (ISM) is notoriously challenging. Motivated by the modern theories of magnetohydrodynamic (MHD) turbulence and turbulence anisotropy, we introduce the Structure Function Analysis (SFA) as a new approach to measure the magnetic-field orientation and estimate the magnetization. We analyze the statistics of turbulent velocities in three-dimensional compressible MHD simulations through the second-order structure functions in both local and global reference frames. In the sub-Alfvénic turbulence with the magnetic energy larger than the turbulent energy, the SFA of turbulent velocities measured in the directions perpendicular and parallel to the magnetic field can be significantly different. Their ratio has a power-law dependence on the Alfvén Mach number MA, which is inversely proportional to the magnetic-field strength. We demonstrate that the anisotropic structure functions of turbulent velocities can be used to estimate both the orientation and strength of magnetic fields. With turbulent velocities measured using different tracers, our approach can be generally applied to probing the magnetic fields in the multiphase ISM.

Keywords: interstellar medium; interstellar magnetic fields; interstellar dynamics
The Effect of Accretion Rate and Composition on the Structure of Ice-rich Super-Earths

It is reasonable to assume that the structure of a planet and the interior distribution of its components are determined by its formation history. We thus follow the growth of a planet from a small embryo through its subsequent evolution. We estimate the accretion rate range based on a protoplanetary disk model at a large-enough distance from the central star for water ice to be a major component. We assume the accreted material to be a mixture of silicate rock and ice, with no H-He envelope, as the accretion timescale is much longer than the time required for the nebular gas to dissipate. We adopt a thermal evolution model that includes accretional heating, radioactive energy release, and separation of ice and rock. Taking the Safronov parameter and the ice-to-rock ratio as free parameters, we compute growth and evolutionary sequences for different parameter combinations, for 4.6 Gyr. We find the final structure to depend significantly on both parameters. Low initial ice-to-rock ratios and high accretion rates, each resulting in an increased heating rate, lead to the formation of extended rocky cores, while the opposite conditions leave the composition almost unchanged and result in relatively low internal temperatures. When rocky cores form, the ice-rich outer mantles still contain rock mixed with the ice. We find that a considerable fraction of the ice evaporates upon accretion, depending on parameters, and assume it is lost, thus the final surface composition and bulk density of the planet do not necessarily reflect the protoplanetary disk composition.

Keywords: super earths; exoplanet formation; exoplanet evolution; exoplanet structure; extrasolar rocky planets; planet formation; surface ices
Detectable Data-driven Features in the Primordial Scalar Power Spectrum

In this work we explore the power of future large-scale surveys to constrain possible deviations from the standard single-field slow-roll inflationary scenario. Specifically, we parameterize possible fluctuations around the almost scale-invariant primordial scalar power spectrum in a model-independent way. We then use their imprints on the simulated matter distribution, as observed by the galaxy clustering and weak lensing probes of Euclid and the Square Kilometer Array, to construct the best constrainable patterns of fluctuations. For comparison, we make similar forecasts for a futuristic CMB-S4-like survey. The modes are found to have similar, yet shifted, patterns, with increasing number of wiggles as the mode number increases. The forecasted constraints are tightest for cosmic microwave background anisotropies and galaxy clustering, depending on the details of the specifications of the survey. As case studies, we explore how two greatly different physically motivated patterns of primordial power spectrum are reconstructed by the proposed modes. We propose a figure of merit based on the amount of information delivered by the modes to truncate the mode hierarchy, which is automatically generated by the analysis.

Keywords: large-scale structure of the universe; computational astronomy; origin of the universe; cosmic microwave background radiation
Water UV-shielding in the Terrestrial Planet-forming Zone: Implications from Water Emission

Mid-infrared spectroscopy is one of the few ways to observe the composition of the terrestrial planet-forming zone, the inner few astronomical units, of protoplanetary disks. The species currently detected in the disk atmosphere, for example, CO, CO2, H2O, and C2H2, are theoretically enough to constrain the C/O ratio on the disk surface. However, thermochemical models have difficulties in reproducing the full array of detected species in the mid-infrared simultaneously. In an effort to get closer to the observed spectra, we have included water UV-shielding as well as more efficient chemical heating into the thermochemical code Dust and Lines. We find that both are required to match the observed emission spectrum. Efficient chemical heating, in addition to traditional heating from UV photons, is necessary to elevate the temperature of the water-emitting layer to match the observed excitation temperature of water. We find that water UV-shielding stops UV photons from reaching deep into the disk, cooling down the lower layers with a higher column. These two effects create a hot emitting layer of water with a column of 1-10 × 1018 cm-2. This is only 1%-10% of the water column above the dust τ = 1 surface at mid-infrared wavelengths in the models and represents <1% of the total water column.

Keywords: astrochemistry; protoplanetary disks
The Infrared Echo of SN2010jl and Its Implications for Shock Breakout Characteristics

SN 2010jl is a Type IIn core-collapse supernova whose radiative output is powered by the interaction of the supernova (SN) shock wave with its surrounding dense circumstellar medium (CSM). After day ~60, its light curve developed a near-infrared (NIR) excess emission from dust. This excess could be a thermal IR echo from preexisting CSM dust, or emission from newly formed dust either in the cooling post-shock region of the CSM, or in the cooling SN ejecta. Recent analysis has shown that dust formation in the CSM can commence only after day ~380, and has also ruled out newly formed ejecta dust as the source of the NIR emission. The early (<380 days) NIR emission can therefore only be attributed to an IR echo. The H-K color temperature of the echo is about 1250 K. The best-fitting model requires the presence of about 1.6 × 10-4 M⊙ of amorphous carbon dust at a distance of 2.2 × 1016 cm from the explosion. The CSM-powered luminosity is preceded by an intense burst of hard radiation generated by the breakout of the SN shock through the stellar surface. The peak burst luminosity seen by the CSM dust is significantly reduced by Thomson scattering in the CSM, but still has the potential of evaporating the dust needed to produce the echo. We show that the survival of the echo-producing dust provides important constraints on the intensity, effective temperature, and duration of the burst.

Keywords: circumstellar shells; circumstellar grains; circumstellar dust; light curves; core-collapse supernovae; shocks
Preferential Heating of Protons over Electrons from Coherent Structures during the First Perihelion of the Parker Solar Probe

The solar wind undergoes significant heating as it propagates away from the Sun; the exact mechanisms responsible for this heating remain unclear. Using data from the first perihelion of the Parker Solar Probe mission, we examine the properties of proton and electron heating occurring within magnetic coherent structures identified by means of the Partial Variance of Increments (PVI) method. Statistically, regions of space with strong gradients in the magnetic field, PVI ≥ 1, are associated with strongly enhanced proton but only slightly elevated electron temperatures. Our analysis indicates a heating mechanism in the nascent solar wind environment facilitated by a nonlinear turbulent cascade that preferentially heats protons over electrons.

Keywords: solar wind; solar coronal heating; interplanetary turbulence; magnetohydrodynamics
Exploring the Origin of Thick Disks Using the NewHorizon and Galactica Simulations

Ever since a thick disk was proposed to explain the vertical distribution of the Milky Way disk stars, its origin has been a recurrent question. We aim to answer this question by inspecting 19 disk galaxies with stellar mass greater than 1010 M⊙ in recent cosmological high-resolution zoom-in simulations: GALACTICA and NEWHORIZON. The thin and thick disks are reasonably reproduced by the simulations with scale heights and luminosity ratios as observed. We then spatially classify the thin and thick disks and find that the thick disk stars are older, metal-poorer, kinematically hotter, and higher in accreted star fraction, while both disks are dominated by the stars formed in situ. Half of the in situ stars in the thick disks are formed before the galaxies develop their disks, and the rest are formed in spatially and kinematically thinner disks and then thickened with time by heating. However, the 19 galaxies have various properties and evolutionary routes, highlighting the need for statistically large samples to draw general conclusions. We conclude from our simulations that the thin and thick disk components are not entirely distinct in terms of formation processes but rather markers of the evolution of galactic disks. Moreover, as the combined result of the thickening of the existing disk stars and the continued formation of young thin disk stars, the vertical distribution of stars does not change much after the disks settle, pointing to the modulation of both orbital diffusion and star formation by the same confounding factor: the proximity of galaxies to marginal stability.

Keywords: galaxy formation
Particle Acceleration and Magnetic Field Amplification by Relativistic Shocks in Inhomogeneous Media

Particle acceleration and magnetic field amplification in relativistic shocks propagating in inhomogeneous media are investigated by three-dimensional magnetohydrodynamical (MHD) simulations and test-particle simulations. The MHD simulations show that the interaction between the relativistic shock and dense clumps amplifies the downstream magnetic field to the value expected from observations of the gamma-ray burst. The test-particle simulations in the electromagnetic field given by the MHD simulation show that particles are accelerated by the downstream turbulence and the relativistic shock. We provide the injection energy to the shock acceleration in this system. If the amplitude of upstream density fluctuations is sufficiently large, low-energy particles are initially accelerated to the injection energy by the downstream turbulence and then rapidly accelerated to higher energies by the relativistic shock. Therefore, the density fluctuation significantly affects particle acceleration in the relativistic shock.

Keywords: cosmic rays; plasma astrophysics; magnetohydrodynamics; gamma-ray bursts; high energy astrophysics; shocks