Sazuna/UAT_keywords huggingface dataset:
Large-scale Molecular Gas Distribution in the M17 Cloud Complex: Dense Gas Conditions of Massive Star Formation?. The non-uniform distribution of gas and protostars in molecular clouds is caused by combinations of various physical processes that are difficult to separate. We explore this non-uniform distribution in the M17 molecular cloud complex that hosts massive star formation activity using the 12CO (J = 1-0) and 13CO (J = 1-0) emission lines obtained with the Nobeyama 45 m telescope. Differences in clump properties such as mass, size, and gravitational boundedness reflect the different evolutionary stages of the M17-H II and M17-IRDC clouds. Clumps in the M17-H II cloud are denser, more compact, and more gravitationally bound than those in M17-IRDC. While M17-H II hosts a large fraction of very dense gas (27%) that has a column density larger than the threshold of ∼1 g cm-2 theoretically predicted for massive star formation, this very dense gas is deficient in M17-IRDC (0.46%). Our HCO+ (J = 1-0) and HCN (J = 1-0) observations with the Taeduk Radio Astronomy Observatory 14 m telescope trace all gas with a column density higher than 3 × 1022 cm-2, confirming the deficiency of high-density (≳105 cm-3) gas in M17-IRDC. Although M17-IRDC is massive enough to potentially form massive stars, its deficiency of very dense gas and gravitationally bound clumps can explain the current lack of massive star formation.

Keywords: Giant molecular clouds, Star formation, Interstellar medium, Protostars, Diffuse molecular clouds
An Analysis of the Shapes of Interstellar Extinction Curves. VIII. The Optical Extinction Structure. New Hubble Space Telescope/STIS optical spectra were obtained for a sample of early-type stars with existing International Ultraviolet Explorer UV spectra. These data were used to construct optical extinction curves whose general properties are discussed elsewhere. In this paper, we identify extinction features in the curves that are wider than diffuse interstellar bands (DIBs) but narrower than the well known broadband variability. This intermediate scale structure, or ISS, contains distinct features whose peaks can contribute a few percent to 20% of the total extinction. Most of the ISS variation can be captured by three principal components. We model the ISS with three Drude profiles and show that their strengths and widths vary from one sight line to another, but their central positions are stable, near 4370, 4870, and 6300 Å. The very broad structure (VBS) in optical curves appears to be a minimum between the 4870 and 6300 Å absorption peaks. We find relations among the fit parameters and provide a physical interpretation of them in terms of a simplistic grain model. Finally, we note that the strengths of the 4370 and 4870 Å features are correlated to the strength of the 2175 Å UV bump, but that the 6300 Å feature is not, and that none of the ISS features are related to R(V). However, we verify that the broadband curvature of the continuous optical extinction is strongly related to R(V).

Keywords: Interstellar dust, Interstellar dust extinction
Flare-like Variability of the Mg II λ2798 Å Emission Line and UV Fe II Band in the Blazar CTA 102. We report on the detection of a statistically significant flare-like event in the Mg II λ 2798 Å emission line and the UV Fe II band of CTA 102 during the outburst of fall 2017. The ratio between the maximum and minimum of λ3000 Å continuum flux for the observation period (2010-2017) is 179 ± 15. Respectively, the max/min ratios 8.1 ± 10.5 and 34.0 ± 45.5 confirmed the variability of the Mg II emission line and of the Fe II band. The highest levels of emission line fluxes recorded coincide with a superluminal jet component traversing through a stationary component located ∼0.1 mas from the 43 GHz core. Additionally, comparing the Mg II line profile in the minimum of activity against the one in the maximum, we found that the latter is broader and blueshifted. As a result of these findings, we can conclude that the non-thermal continuum emission produced by material in the jet moving at relativistic speeds is related to the broad emission line fluctuations. Consequently, these fluctuations are also linked to the presence of broad-line region (BLR) clouds located ∼25 pc from the central engine, outside the inner parsec, where the canonical BLR is located. Our results suggest that during strong activity in CTA 102, the source of non-thermal emission and broad-line clouds outside the inner parsec introduces uncertainties in the estimates of black hole (BH) mass. Therefore, it is important to estimate the BH mass, using single-epoch or reverberation mapping techniques, only with spectra where the continuum luminosity is dominated by the accretion disk.

Keywords: Blazars, Active galaxies, Relativistic jets, Emission line galaxies, Gamma-ray astronomy
On the Absence of High-redshift AGNs: Little Growth in the Supermassive Black Hole Population at High Redshifts. We search for high-redshift (z &gt; 4.5) X-ray active galactic nuclei (AGNs) in the deep central (off-axis angle &lt; 5'7) region of the 7 Ms Chandra Deep Field-South X-ray image. We compile an initial candidate sample from direct X-ray detections. We then probe more deeply in the X-ray data by using preselected samples with high spatial resolution near-infrared (NIR)/mid-infrared (MIR) (Hubble Space Telescope (HST) 1.6 μm and Spitzer 4.5 μm) and submillimeter (ALMA 850 μm) observations. The combination of the NIR/MIR and submillimeter preselections allows us to find X-ray sources with a wide range of dust properties and spectral energy distributions (SEDs). We use the SEDs from the optical to the submillimeter to determine if previous photometric redshifts were plausible. Only five possible z &gt; 5 X-ray AGNs are found, all of which might also lie at lower redshifts. If they do lie at high redshifts, then two are Compton-thick AGNs. Three of the five are ALMA 850 μm sources, including the two Compton-thick AGN candidates. We find that (I) the number density of X-ray AGN drops rapidly at high redshifts, (II) the detected AGNs do not contribute significantly to photoionization at z &gt; 5, and (III) the measured X-ray light density over z = 5-10 implies a very low black hole accretion density with very little growth in the black hole mass density in this redshift range.

Keywords: Cosmology, Supermassive black holes, Observational cosmology, X-ray active galactic nuclei
Observations of a GX 301-2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM. The accretion-powered X-ray pulsar GX 301-2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late 2018 December, with contiguous observations by the Neutron star Interior Composition Explorer Mission (NICER) X-ray telescope, the Swift X-ray Telescope and Burst Alert Telescope, and the Fermi Gamma-ray Burst Monitor spanning several months. The observations detected the pulsar in a rare apastron flaring state coinciding with a significant spin up of the pulsar discovered with the Fermi Gamma-ray Burst Monitor. The X-Calibur, NICER, and Swift observations reveal a pulse profile strongly dominated by one main peak, and the NICER and Swift data show strong variation of the profile from pulse to pulse. The X-Calibur observations constrain for the first time the linear polarization of the 15-35 keV emission from a highly magnetized accreting neutron star, indicating a polarization degree of (27-27+38) % (90% confidence limit) averaged over all pulse phases. We discuss the spin up and the X-ray spectral and polarimetric results in the context of theoretical predictions. We conclude with a discussion of the scientific potential of future observations of highly magnetized neutron stars with the more sensitive follow-up mission XL-Calibur.

Keywords: Neutron stars, X-ray astronomy, Spectropolarimetry, Bianchi cosmology, High mass x-ray binary stars
The Chandra High-resolution X-Ray Spectrum of Quiescent Emission from Sgr A*. In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than expected for its environment. This problem has motivated a host of theoretical models to explain radiatively inefficient accretion flows. The Chandra Galactic Center X-ray Visionary Program obtained approximately 3 Ms (1 month) of Chandra high-energy transmission grating (HETG) data, offering the only opportunity to examine the quiescent X-ray emission of Sgr A* with high-resolution spectroscopy. Utilizing custom background regions and filters for removing overlapping point sources, this work provides the first-ever look at stacked HETG spectra of Sgr A*. We model the background data sets with a cubic spline and fit the unbinned Sgr A* spectra with a simple parametric model of a power law plus Gaussian lines under the effects of interstellar extinction. We detect a strong 6.7 keV iron emission line in the HEG spectra and a 3.1 keV emission line in the MEG spectra. In all cases, the line centroids and equivalent widths are consistent with those measured from low-resolution CCD spectra. An examination of the unbinned, stacked HEG ± 1 spectrum reveals fine structure in the iron line complex. In addition to resolving the resonant and forbidden lines from He-like iron, there are apparent emission features arising with higher statistical significance at lower energy, potentially associated with Fe XX-XXIV ions in a ∼1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we release the cleaned and stacked Sgr A* and background HETG spectra to the public as a special legacy data set.

Keywords: Accretion, Supermassive black holes, High resolution spectroscopy, Galactic center
Fast Radio Bursts from Activity of Neutron Stars Newborn in BNS Mergers: Offset, Birth Rate, and Observational Properties. Young neutron stars (NSs) born in core-collapse explosions are promising candidates for the central engines of fast radio bursts (FRBs), since the first localized repeating burst FRB 121102 occurs in a star-forming dwarf galaxy similar to the host galaxies of superluminous supernovae and long gamma-ray bursts. However, FRB 180924 and FRB 190523 are localized to massive galaxies with low rates of star formation, compared with the host of FRB 121102. The offsets between the bursts and host centers are about 4 and 29 kpc for FRB 180924 and FRB 190523, respectively. These host properties are similar to those of short gamma-ray bursts (GRBs), which are produced by binary neutron star (BNS) or NS-black hole mergers. Therefore, the NSs powering FRBs may be formed in BNS mergers. In this paper, we study BNS merger rates and merger times, and predict the most likely merger locations for different types of host galaxies using the population synthesis method. We find that the BNS merger channel is consistent with the recently reported offsets of FRB 180924 and FRB 190523. The offset distribution of short GRBs is well reproduced by population synthesis using a galaxy model similar to that of GRB hosts. The event rate of FRBs (including non-repeating and repeating), is larger than those of BNS mergers and short GRBs, and requires a large fraction of observed FRBs emitting several bursts. Using curvature radiation by bunches in NS magnetospheres, we also predict the observational properties of FRBs from BNS mergers, including the dispersion measure and rotation measure. At late times (t ≥ 1 yr), the contribution to dispersion measure and rotation measure from BNS merger ejecta can be neglected.

Keywords: Gamma-ray bursts, Binary stars, Radio bursts, Gravitational waves, Magnetars
Prevalence of Complex Organic Molecules in Starless and Prestellar Cores within the Taurus Molecular Cloud. The detection of complex organic molecules (COMs) toward dense, collapsing prestellar cores has sparked interest in the fields of astrochemistry and astrobiology, yet the mechanisms for COM formation are still debated. It was originally believed that COMs first form in ices, only to be irradiated by UV radiation from the surrounding interstellar radiation field as well as forming protostars, and subsequently photodesorbed into the gas phase. However, starless and prestellar cores do not have internal protostars to heat up and sublimate the ices. Alternative models using chemical energy have been developed to explain the desorption of COMs, yet in order to test these models, robust measurements of COM abundances are needed toward representative samples of cores. We have conducted a large sample survey of 31 starless and prestellar cores in the Taurus molecular cloud, detecting methanol (CH3OH) in 100% of the cores targeted and acetaldehyde (CH3CHO) in 70%. At least two transition lines of each molecule were measured, allowing us to place tight constraints on excitation temperature, column density, and abundance. Additional mapping of methanol revealed extended emission detected down to AV as low as ∼3 mag. We find that COMs are detectable in the gas phase and are being formed early, at least hundreds of thousands of years prior to star and planet formation. The precursor molecule, CH3OH, may be chemically linked to the more complex CH3CHO; however, higher spatial resolution maps are needed to further test chemical models.

Keywords: Star formation, Dense interstellar clouds, Astrochemistry
High-z Dusty Star-forming Galaxies: A Top-heavy Initial Mass Function?. Recent estimates point to abundances of z &gt; 4 submillimeter galaxies far above model predictions. The matter is still debated. According to some analyses the excess may be substantially lower than initially thought and perhaps accounted for by flux boosting and source blending. However, there is no general agreement on this conclusion. An excess of z &gt; 6 dusty galaxies has also been reported albeit with poor statistics. On the other hand, evidence of a top-heavy initial mass function (IMF) in high-z starburst galaxies has been reported in the past decades. This would translate into a higher submillimeter luminosity of dusty galaxies at fixed star formation rate, I.e., into a higher abundance of bright high-z submillimeter galaxies than expected for a universal Chabrier IMF. Exploiting our physical model for high-z protospheroidal galaxies, we find that part of the excess can be understood in terms of an IMF somewhat top-heavier than Chabrier. Such an IMF is consistent with that recently proposed to account for the low 13C/18O abundance ratio in four dusty starburst galaxies at z = 2-3. However, extreme top-heavy IMFs are inconsistent with the submillimeter counts at z &gt; 4.

Keywords: Submillimeter astronomy, High-redshift galaxies, Initial mass function, Galaxy evolution
Simulations of Young Type Ia Supernova Remnants Undergoing Shock Acceleration in a Turbulent Medium. Two-dimensional cylindrical magnetohydrodynamic (MHD) simulations are implemented to investigate the dynamical properties of young type Ia supernova remnants (SNRs) undergoing shock acceleration in a turbulent medium. In our simulations, an MHD code is coupled with a semianalytical kinetic treatment of shock acceleration by means of a time-dependent effective adiabatic index. Large-scale density and magnetic field fluctuations are calculated and mapped into the computational domain before simulations. The above configurations allow us to study the time-dependent dynamical properties and magnetic field structure of a benchmark SNR undergoing shock acceleration in a turbulent medium, along with the relative positions of the contact discontinuity. Our simulation results reveal that there is a rippled forward shock, a thinner shocked ejecta layer and a denser, narrower intershock region. The resulting net effect is a higher density difference between the shocked ejecta and the shocked interstellar medium, leading to a growth of the Rayleigh-Taylor instability. The amplified magnetic field occurs not only at the contact discontinuity but also near the immediate downstream of the shock. The spatial location of the maximum magnetic field is in the vicinity of immediate downstream, which is different with Guo et al. Our derived profiles of the relative contact discontinuity positions are compatible with the results of two typical young type Ia SNRs: SN 1006 and Tycho, with the lowest value reaching ∼1.02 for both cases. Moreover, we find no obvious ejecta protrusions beyond the main forward shock.

Keywords: Supernova remnants, Interstellar medium
Black Hole Mass Function and Its Evolution—The First Prediction for the Einstein Telescope. Knowledge of the black hole mass function (BHMF) and its evolution would help us understand the origin of BHs and how BH binaries formed at different stages in the history of the universe. We demonstrate the ability of a future third-generation gravitational-wave (GW) detector - the Einstein Telescope (ET) - to infer the slope of the BHMF and its evolution with redshift. We perform a Monte Carlo simulation of the measurements of chirp signals from binary BH systems (BBH) that could be detected by ET, including the BH masses and their luminosity distances (dL). We use the mass of a primary black hole in each binary system to infer the BHMF as a power-law function with slope parameter α. Taking into account the bias that could be introduced by the uncertainty of measurements and by the selection effect, we carried out the numerical tests and found that only 1000 GW events registered by ET (∼1% of its yearly detection rate) could accurately infer the α with a precision of α ∼ 0.1. Furthermore, we investigate the validity of our method to recover a scenario where α evolves with redshift as α(z)= α0 + α1 {z}/{1+z}. Taking a thousand GW events and using dL as the redshift estimator, our tests show that one could infer the value of evolving parameter α1 accurately at the uncertainty level of ∼0.5. Our numerical tests verify the reliability of our method. The uncertainty levels of the inferred parameters can be trusted directly for several sets of the parameters we assumed, yet they should not be treated as general.

Keywords: Gravitational waves, Black holes
Upward Overshooting in Turbulent Compressible Convection. III. Calibrate Parameters for One-dimensional Reynolds Stress Model. In this paper, we calibrate the coefficients for the one-dimensional Reynolds stress model (RSM) with the data generated from the three-dimensional (3D) numerical simulations of upward overshooting in turbulent compressible convection. It has been found that the calibrated convective and isotropic coefficients are almost the same as those calibrated in the pure convection zone. However, the calibrated diffusive coefficients differ significantly from those calibrated in the pure convection zone. We suspect that the diffusive effect induced by the boundary is stronger than by the adjacent stable zone. We have checked the validity of the downgradient approximation (DGA). We find that the prediction of the DGA on the third-order moments (TOMs) is unsatisfactory. However, the prediction on their derivatives is much better. It explains why the performance of the RSM is reasonable in application to the real stars. With the calibrated coefficients, we have solved the full set of nonlocal turbulent equations on RSM. We find that the RSM has successfully produced the thermal adjustment layer and turbulent dissipation layer, which were identified in the 3D numerical simulations. We suggest to use the inflection point of the auto-correlation of temperature perturbation and the Péclet number as the indicators on measuring the extents of the thermal adjustment layer and turbulent dissipation layer, respectively. This result may offer a practical guidance on the application of the RSM in 1D stellar structure and evolution models.

Keywords: Stellar interiors, Stellar convective zones, Stellar structures, Hydrodynamical simulations, Stellar cores
FOXSI-2 Solar Microflares. I. Multi-instrument Differential Emission Measure Analysis and Thermal Energies. In this paper we present the differential emission measures (DEMs) of two sub-A class microflares observed in hard X-rays (HXRs) by the FOXSI-2 sounding rocket experiment, on 2014 December 11. The second Focusing Optics X-ray Solar Imager (FOXSI) flight was coordinated with instruments X-ray Telescope (Hinode/XRT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), which provided observations in soft X-rays and Extreme Ultraviolet. This unique data set offers an unprecedented temperature coverage, useful for characterizing the plasma temperature distribution of microflares. By combining data from FOXSI-2, XRT, and AIA, we determined a well-constrained DEM for the microflares. The resulting DEMs peak around 3 MK and extend beyond 10 MK. The emission measures determined from FOXSI-2 were lower than 1026 cm-5 for temperatures higher than 5 MK; faint emission in this range is best measured in HXRs. The coordinated FOXSI-2 observations produce one of the few definitive measurements of the distribution and the amount of plasma above 5 MK in microflares. We utilize the multi-thermal DEMs to calculate the amount of thermal energy released during both the microflares as ∼5.0 × 1028 erg for Microflare 1 and ∼1.6 × 1028 erg for Microflare 2. We also show the multi-thermal DEMs provide more comprehensive thermal energy estimates than isothermal approximation, which systematically underestimates the amount of thermal energy released.

Keywords: Solar corona, Solar active regions, Solar flares, Solar x-ray emission
Stronger Southward Magnetic Field and Geoeffectiveness of ICMEs Containing Prominence Materials Measured from 1998 to 2011. Interplanetary coronal mass ejections (ICMEs) could be classified into magnetic clouds (MCs) and non-MCs according to their magnetic field signatures, and into prominence-inside ICMEs (PIs) and non-PIs based on whether they contain colder and higher helium abundance plasmas than the solar wind. It is known that the MCs often lead to magnetic storms. However, whether or not the PIs have significant geoeffectiveness is unclear. This statistical work studies the southward interplanetary magnetic field (IMF) magnitude of the PIs, and the related magnetic storms' level. The data include the IMF and plasma moments measured by ACE and WIND, and the Dst index from 1998 to 2011. The hypothesis test based on the proportions of two groups is used to analyze 95 ICMEs related to single storms (SSs). The results show that the magnetic storms caused by the PIs mostly distribute at a strong level, while that caused by the non-PIs and by all the 95 ICMEs mostly distribute at a moderate level. The PIs have a significantly higher probability of generating SSs than the non-PIs. Moreover, the MCs containing carbon-cold and helium-enhanced materials (MC&amp;PIs) have the highest fraction of minimum Bz, less than -11 nT. Since the MC&amp;PIs have large-scale magnetic flux rope and prominence material, the stronger southward IMF is probably provided by the prominence. It is in accordance with the observed injection of enhanced twisted flux ropes to prominence. Therefore, the detailed eruption and propagation processes of the three-part coronal mass ejections deserve more concern from a space weather perspective.

Keywords: Geomagnetic fields, Space weather, Solar prominences, Solar coronal mass ejections