Sazuna/UAT_keywords huggingface dataset:
Infrared Dark Clouds and High-mass Star Formation Activity in Galactic Molecular Clouds. Ever since their discovery, infrared dark clouds (IRDCs) are generally considered to be the sites just at the onset of high-mass (HM) star formation. In recent years, it has been realized that not all IRDCs harbor HM young stellar objects (YSOs). Only those IRDCs satisfying a certain mass-size criterion, or equivalently above a certain threshold density, are found to contain HMYSOs. In all cases, IRDCs provide ideal conditions for the formation of stellar clusters. In this paper, we study the massive stellar content of IRDCs to readdress the relation between IRDCs and HM star formation. For this purpose, we have identified all IRDCs associated with a sample of 12 Galactic molecular clouds (MCs). The selected MCs have been the target of a systematic search for YSOs in an earlier study. The cataloged positions of YSOs have been used to search all YSOs embedded in each identified IRDC. In total, we have found 834 YSOs in 128 IRDCs. The sample of IRDCs have mean surface densities of 319 ${M}_{\odot }\,{\mathrm{pc}}^{-2}$ , mean mass of 1062 ${M}_{\odot }$ , and a mass function power-law slope -1.8, which are similar to the corresponding properties for the full sample of IRDCs and resulting physical properties in previous studies. We find that all those IRDCs containing at least one intermediate to HM young star satisfy the often-used mass-size criterion for forming HM stars. However, not all IRDCs satisfying the mass-size criterion contain HM stars. We find that the often-used mass-size criterion corresponds to 35% probability of an IRDC forming a massive star. Twenty-five (20%) of the IRDCs are potential sites of stellar clusters of mass more than 100 ${M}_{\odot }$ .

Keywords: Infrared dark clouds, Protoclusters, Young stellar objects, Star formation, Interstellar medium, Protostars
A Study of Millimeter Variability in FUor Objects. FU Orionis objects (FUors) are rapidly accreting, pre-main-sequence objects that are known to exhibit large outbursts at optical and near-infrared wavelengths, with post-eruption, small-scale photometric variability superimposed on longer-term trends. In contrast, little is known about the variability of FUors at longer wavelengths. To explore this further, we observed six FUor objects using the NOrthern Extended Millimeter Array (NOEMA) and for a subset of three objects we obtained coordinated observations with NOEMA and the Lowell Discovery Telescope. In combination with previously published NOEMA observations from 2014, our 2017 observations of V1735 Cyg provide the first detection of variability in an FUor object at 2.7 mm. In the absence of significant optical variability, we discount the possibility that the millimeter flux density changed as a result of irradiation from the central disk. In addition, a change in the dust mass due to infall is highly unlikely. A plausible explanation for the change in 2.7 mm flux density is variability in free-free emission due to changes in the object's jet/wind. Thus, it may be that free-free emission in some FUor objects is significant at ∼3 mm and must be considered when deriving disk masses in order to help constrain the mechanism responsible for triggering FUor outbursts.

Keywords: Accretion, FU Orionis stars, T Tauri stars, Star formation, Stellar accretion disks
A Measurement of the Degree-scale CMB B-mode Angular Power Spectrum with POLARBEAR. We present a measurement of the B-mode polarization power spectrum of the cosmic microwave background (CMB) using data taken from 2014 July to 2016 December with the POLARBEAR experiment. The CMB power spectra are measured using observations at 150 GHz with an instantaneous array sensitivity of ${\mathrm{NET}}_{\mathrm{array}}=23\,\mu {\rm{K}}\sqrt{{\rm{s}}}$ on a 670 square degree patch of sky centered at (R.A., decl.) = (+0h12m0s, -59°18'). A continuously rotating half-wave plate is used to modulate polarization and to suppress low-frequency noise. We achieve 32 μK arcmin effective polarization map noise with a knee in sensitivity of ℓ = 90, where the inflationary gravitational-wave signal is expected to peak. The measured B-mode power spectrum is consistent with a ΛCDM lensing and single dust component foreground model over a range of multipoles 50 ≤ ℓ ≤ 600. The data disfavor zero ${C}_{{\ell }}^{\mathrm{BB}}$ at 2.2σ using this ℓ range of POLARBEAR data alone. We cross-correlate our data with Planck full mission 143, 217, and 353 GHz frequency maps and find the low-ℓ B-mode power in the combined data set to be consistent with thermal dust emission. We place an upper limit on the tensor-to-scalar ratio r &lt; 0.90 at the 95% confidence level after marginalizing over foregrounds.

Keywords: Cosmology, Cosmic microwave background radiation, Observational cosmology, Cosmic inflation
Chemical Desorption versus Energy Dissipation: Insights from Ab Initio Molecular Dynamics of HCO· Formation. Molecular clouds are the cold regions of the Milky Way where stars form. They are enriched by rather complex molecules. Many of these molecules are believed to be synthesized on the icy surfaces of the interstellar submicron-sized dust grains that permeate the Galaxy. At 10 K thermal desorption is inefficient and, therefore, why these molecules are found in the cold gas has tantalized astronomers for years. The assumption of the current models, called chemical desorption, is that the molecule formation energy released by the chemical reactions at the grain surface is partially absorbed by the grain and the remaining energy causes the ejection of the newly formed molecules into the gas. Here we report accurate ab initio molecular dynamics simulations aimed at studying the fate of the energy released by the first reaction of the H· addition chain to CO, H· + CO $\to $ HCO·, occurring on a crystalline ice surface model. We show that about 90% of the HCO· formation energy is injected toward the ice in the first picosecond, leaving HCO· with an energy content (10-15 kJ mol-1) of less than half its binding energy (30 kJ mol-1). As a result, in agreement with laboratory experiments, we conclude that chemical desorption is inefficient for this specific system, namely H· + CO on crystalline ice. We suspect this behavior to be quite general when dealing with hydrogen bonds, which are responsible for both the cohesive energy of the ice mantle and the interaction with adsorbates, as HCO·, even though ad hoc simulations are needed to draw specific conclusions on other systems.

Keywords: Interstellar dust processes, Astrochemistry, Pre-biotic astrochemistry, Solid matter physics
Thermally Unstable Cooling Stimulated by Uplift: The Spoiler Clusters. Chandra X-ray observations are analyzed for five galaxy clusters whose atmospheric cooling times, entropy parameters, and ratios of cooling time to freefall time within the central galaxies lie below 1 Gyr, below 30 keV cm2, and between 20 ≲ min(tcool/tff) ≲ 50, respectively. These thermodynamic properties are commonly associated with molecular clouds, bright Hα emission, and star formation in central galaxies. However, all have Hα luminosities below 1040 erg s-1 in the ACCEPT database. Star formation and molecular gas are absent at the levels seen in other central galaxies with similar atmospheric properties. Only RBS 0533 may host a radio/X-ray bubble, which are commonly observed in cooling atmospheres. Signatures of uplifted, high-metallicity atmospheric gas are absent. Their atmospheres are apparently thermodynamically stable despite the absence of strong nuclear feedback. We suggest that extended filaments of nebular emission and associate molecular clouds are absent at appreciable levels because their central radio sources have failed to lift low-entropy atmospheric gas to an altitude where the ratio of the cooling time to the freefall time falls below unity and the gas becomes thermally unstable.

Keywords: X-ray astronomy, Galaxy clusters, Active galactic nuclei, Brightest cluster galaxies, Intracluster medium
Implications of Inhomogeneous Metal Mixing for Stellar Archaeology. The first supernovae enrich the previously pristine gas with metals, out of which the next generation of stars form. Based on hydrodynamical simulations, we develop a new stochastic model to predict the metallicity of star-forming gas in the first galaxies. On average, in internally enriched galaxies, the metals are well mixed with the pristine gas. However, in externally enriched galaxies, the metals cannot easily penetrate into the dense gas, which yields a significant metallicity difference between the star-forming and average gas inside a halo. To study the consequences of this effect, we apply a semianalytical model to Milky Way-like dark matter merger trees and follow stellar fossils from high redshift until the present day with a novel realistic metal mixing recipe. We calibrate the model to reproduce the metallicity distribution function (MDF) at low metallicities and find that a primordial initial mass function (IMF) with a slope of ${dN}/{dM}\propto {M}^{-0.5}$ from 2 to $180\,{M}_{\odot }$ best reproduces the MDF. Our improved model for inhomogeneous mixing can have a large impact for individual minihalos but does not significantly influence the modeled MDF at [Fe/H] ≳ -4 or the best-fitting Population III IMF.

Keywords: Population III stars, Interstellar dynamics, Galaxy chemical evolution, Chemical enrichment, Interstellar medium
Orbital and Mass Constraints of the Young Binary System IRAS 16293-2422 A. We present 3 mm ALMA continuum and line observations at resolutions of 6.5 au and 13 au, respectively, toward the Class 0 system IRAS 16293-2422 A. The continuum observations reveal two compact sources toward IRAS 16293-2422 A, coinciding with compact ionized gas emission previously observed at radio wavelengths (A1 and A2), confirming the long-known radio sources as protostellar. The emission toward A2 is resolved and traces a dust disk with an FWHM size of ∼12 au, while the emission toward A1 sets a limit to the FWHM size of the dust disk of ∼4 au. We also detect spatially resolved molecular kinematic tracers near the protostellar disks. Several lines of the J = 5-4 rotational transition of HNCO, NH2CHO, and t-HCOOH are detected, with which we derived individual line-of-sight velocities. Using these together with the CS (J = 2-1), we fit Keplerian profiles toward the individual compact sources and derive masses of the central protostars. The kinematic analysis indicates that A1 and A2 are a bound binary system. Using this new context for the previous 30 yr of Very Large Array observations, we fit orbital parameters to the relative motion between A1 and A2 and find that the combined protostellar mass derived from the orbit is consistent with the masses derived from the gas kinematics. Both estimations indicate masses consistently higher (0.5 ≲ M1 ≲ M2 ≲ 2 ${M}_{\odot }$ ) than previous estimations using lower-resolution observations of the gas kinematics. The ALMA high-resolution data provides a unique insight into the gas kinematics and masses of a young deeply embedded bound binary system.

Keywords: Close binary stars, Star formation, Protostars, Circumstellar dust, Circumstellar gas
Cradle(s) of the Sun. The Sun likely formed as part of a group of stars. A close stellar flyby by one of the solar siblings is probably responsible for the sharp outer edge in the solar system's mass distribution. The frequency of such close flybys can be used to determine the likely type of birth environment of the solar system. Young stellar groups develop very quickly, expanding significantly within just a few million years. Here we model this strong dynamical development of young stellar groups and determine the resulting close flyby history. We find that solar system equivalents are predominantly produced in areas with stellar densities in the range 5 × 104 pc-3 &lt; nlocal &lt; 2 × 105 pc-3. Remarkably, we find that only two very distinct types of stellar groups can be considered as serious contestants as the cradle of the Sun—high-mass, extended associations (Mc &gt; 20,000 M⊙) and intermediate-mass, compact clusters (Mc &lt; 3000 M⊙). Present-day counterparts would be the association NGC 2244 and the M44 cluster, respectively. In these two types of stellar groups, close flybys take place at a sufficiently high rate, while not being too destructive either. A final decision between these two remaining options will require the incorporation of constraints from cosmochemical studies.

Keywords: Gravitational interaction, Solar system formation, Young star clusters, N-body simulations
The Local Star Formation Rate Surface Density and Metallicity Relation for Star-forming Galaxies. We study the relations between gas-phase metallicity (Z), local stellar mass surface density (Σ*), and the local star formation surface density (ΣSFR) in a sample of 1120 star-forming galaxies from the MaNGA survey. At fixed Σ* the local metallicity increases as ΣSFR decreases or vice versa for metallicity calibrators of N2 and O3N2. Alternatively, at fixed ΣSFR metallicity increases as Σ* increases, but in the high mass region, the trend is flatter. However, the dependence of metallicity on ΣSFR nearly disappears for N2O2 and N2S2 calibrators. We investigate the local metallicity against ΣSFR with different metallicity calibrators and find negative/positive correlations depending on the choice of the calibrator. We demonstrate that the O32 ratio (or ionization parameter) is probably dependent on star formation rate at fixed local stellar mass surface density. Additionally, the shape of Σ*-Z-ΣSFR (fundamental metallicity relation; FMR) depends on metallicity calibrator and stellar mass range. Due to the large discrepancy between the empirical fitting-based (N2, O3N2) electronic temperature metallicity and the photoionization model-dependent (N2O2, N2S2) metallicity calibrations, we conclude that the selection of metallicity calibration affects the existence of FMR on ΣSFR.

Keywords: Galaxy chemical evolution, Interstellar emissions, Galaxy abundances, Galaxy evolution, Interstellar medium
Element Stratification in the Middle-aged SN Ia Remnant G344.7-0.1. Despite their importance, a detailed understanding of Type Ia supernovae (SNe Ia) remains elusive. X-ray measurements of the element distributions in supernova remnants (SNRs) offer important clues for understanding the explosion and nucleosynthesis mechanisms for SNe Ia. However, it is challenging to observe the entire ejecta mass in X-rays for young SNRs, because the central ejecta may not have been heated by the reverse shock yet. Here we present over 200 kilosecond Chandra observations of the Type Ia SNR G344.7-0.1, whose age is old enough for the reverse shock to have reached the SNR center, providing an opportunity to investigate the distribution of the entire ejecta mass. We reveal a clear stratification of heavy elements with a centrally peaked distribution of the Fe ejecta surrounded by intermediate-mass elements (IMEs: Si, S, Ar Ca) with an arc-like structure. The centroid energy of the Fe K emission is marginally lower in the central Fe-rich region than in the outer IME-rich regions, suggesting that the Fe ejecta were shock-heated more recently. These results are consistent with the prediction for standard SN Ia models, where the heavier elements are synthesized in the interior of an exploding white dwarf. We find, however, that the peak location of the Fe K emission is slightly offset to the west with respect to the geometric center of the SNR. This apparent asymmetry is likely due to the inhomogeneous density distribution of the ambient medium, consistent with our radio observations of the ambient molecular and neutral gas.

Keywords: Supernova remnants, Interstellar medium
The Warm-Hot, Extended, Massive Circumgalactic Medium of NGC 3221: An XMM-Newton Discovery. Using Suzaku data, we had found a 3.4σ evidence for the X-ray emitting warm-hot circumgalactic medium (CGM) in the L⋆ galaxy NGC 3221. Here we present XMM-Newton data and outline an efficient, rigorous, and well-defined method to extract the faint CGM signal. We confirm the CGM detection at 4σ significance within 30-200 kpc of the galaxy. We claim with 99.62% confidence that the CGM is extended beyond 150 kpc. The average temperature of the CGM is ${2.0}_{-0.3}^{+0.2}\times {10}^{6}$ K, but it is not isothermal. We find suggestive evidence for a declining temperature gradient out to 125 kpc and for supervirial temperature within 100 kpc. While a supervirial temperature component has been detected in the Milky Way CGM, this is the first time a temperature gradient has been observed in the warm-hot CGM of any spiral galaxy. The emission measure profile is well-fit with either a β-model or a constant-density profile. Deeper data are required to constrain the temperature and density profiles. We also confirm the Suzaku result that the warm-hot CGM is one of the most massive baryon components of NGC 3221 and can account for the missing galactic baryons.

Keywords: X-ray astronomy, Galaxy environments, Diffuse radiation, Missing mass, Hot ionized medium, Circumgalactic medium, Extragalactic astronomy, Diffuse x-ray background
The Role of Turbulence for Heating Plasmas in Eruptive Solar Flares. Magnetohydrodynamic turbulence is ubiquitous in the process of solar eruptions, and it is crucial for the fast release of energy and the formation of complex thermal structures that have been found in observations. In this paper, we focus on the turbulence in two specific regions: inside the current sheet (CS) and above the flare loops, considering the standard flare model. The gravitationally stratified solar atmosphere is used in MHD simulations, which include the Lundquist number of S = 106, thermal conduction, and radiative cooling. The numerical results are generally consistent with previous simulation work, especially the thermal structures and reconnection rate in flare phases. We can observe the formation of multiple termination shocks (TSs) as well as plasmoid collisions, which make the region above the loop-top more turbulent and heat plasmas to the higher temperature. The spectrum studies show that the property of the MHD turbulence inside the CS is anisotropic, while it is quasi-isotropic above the loop-top. The magnetic spectrum becomes softer when the plasmoids interact with the multiple TSs. Meanwhile, synthetic images and light curves of the Solar Dynamics Observatory/Atmospheric Imaging Assembly 94, 131, 171, 304, and 193 Å channels show intermittent radiation enhancement by turbulence above the loop-top. The spectrum study of the radiation intensity in these five wavelengths gives quite different power indices at the same time. In particular, quasiperiodic pulsations (QPPs) in the turbulent region above the loop-top are investigated, and we also confirm that the heating for plasmas via turbulence is an important contributor to the source of QPPs.

Keywords: Termination shock, Solar flares, Solar magnetic reconnection, Magnetohydrodynamical simulations
Coherent Stellar Motion in Galactic Spiral Arms by Swing Amplification. We perform local N-body simulations of disk galaxies and investigate the evolution of spiral arms. We calculate the time autocorrelation of the surface density of spiral arms and find that the typical evolution timescale is described by the epicycle period. We investigate the distribution of the orbital elements of stars and find that in spiral arms the epicycle motions of stars are in phase while the spatial distribution of the guiding center is nearly uniform. These facts clearly show that the phase synchronization of the epicycle motion takes place, which is theoretically predicted by the swing amplification.

Keywords: Spiral arms, Galaxy dynamics, N-body simulations
The Variable and Non-variable X-Ray Absorbers in Compton-thin Type II Active Galactic Nuclei. We have conducted an extensive X-ray spectral variability study of a sample of 20 Compton-thin type II galaxies using broadband spectra from XMM-Newton, Chandra, and Suzaku. The aim is to study the variability of the neutral intrinsic X-ray obscuration along the line of sight and investigate the properties and location of the dominant component of the X-ray-obscuring gas. The observations are sensitive to absorption columns of ${N}_{{\rm{H}}}$ ∼ 1020.5-24 cm-2 of fully and partially covering neutral and/or lowly ionized gas on timescales spanning days to well over a decade. We detected variability in the column density of the full-covering absorber in 7/20 sources, on timescales of months to years, indicating a component of compact-scale X-ray-obscuring gas lying along the line of sight of each of these objects. Our results imply that torus models incorporating clouds or over-dense regions should account for line-of-sight column densities as low as ∼a few ×1021 cm-2. However, 13/20 sources yielded no detection of significant variability in the full-covering obscurer, with upper limits of ∆NH spanning 1021-23 cm-2. The dominant absorbing media in these systems could be distant, such as kiloparsec-scale dusty structures associated with the host galaxy, or a homogeneous medium along the line of sight. Thus, we find that overall, strong variability in full-covering obscurers is not highly prevalent in Compton-thin type IIs, at least for our sample, in contrast to previous results in the literature. Finally, 11/20 sources required a partial-covering, obscuring component in all or some of their observations, consistent with clumpy near-Compton-thick compact-scale gas.

Keywords: Quasar absorption line spectroscopy, Active galaxies, Interstellar medium, Supermassive black holes
Accurate Treatment of Comptonization in X-Ray Illuminated Accretion Disks. A large fraction of accreting black hole and neutron star systems present clear evidence of the reprocessing of X-rays in the atmosphere of an optically thick accretion disk. The main hallmarks of X-ray reflection include fluorescent K-shell emission lines from iron (∼6.4-6.9 keV), the absorption iron K-edge (∼7-9 keV), and a broad featureless component known as the Compton hump (∼20-40 keV). This Compton hump is produced as the result of the scattering of high-energy photons (E ≳ 10 keV) of the relatively colder electrons (Te ∼ 105-107 K) in the accretion disk, in combination with photoelectric absorption from iron. The treatment of this process in most current models of ionized X-ray reflection has been done using an approximated Gaussian redistribution kernel. This approach works sufficiently well up to ∼100 keV, but it becomes largely inaccurate at higher energies and at relativistic temperatures (Te ∼ 109 K). We present new calculations of X-ray reflection using a modified version of our code xillver, including an accurate solution for Compton scattering of the reflected unpolarized photons in the disk atmosphere. This solution takes into account quantum electrodynamic and relativistic effects allowing the correct treatment of high photon energies and electron temperatures. We show new reflection spectra computed with this model, and discuss the improvements achieved in reproducing the correct shape of the Compton hump, the discrepancies with previous calculations, and the expected impact of these new models in the interpretation of observational data.

Keywords: Accretion, Black hole physics, Atomic spectroscopy, Stellar accretion disks, Radiative transfer simulations, Astronomical simulations