Sazuna/UAT_keywords huggingface dataset:
The Effect of Stream Interaction Regions on ICME Structures Observed in Longitudinal Conjunction. We study two interplanetary coronal mass ejections (ICMEs) observed at Mercury and at 1 au by spacecraft in longitudinal conjunction, investigating the question: what causes the drastic alterations observed in some ICMEs during propagation, while other ICMEs remain relatively unchanged? Of the two ICMEs, the first one propagated relatively self-similarly, while the second one underwent significant changes in its properties. We focus on the presence or absence of large-scale corotating structures in the ICME propagation space between Mercury and 1 au, which have been shown to influence the orientation of ICME magnetic structures and the properties of ICME sheaths. We determine the flux rope orientation at the two locations using force-free flux rope fits as well as the classification by Nieves-Chinchilla et al. We also use measurements of plasma properties at 1 au, the size evolution of the sheaths and magnetic ejecta with heliocentric distance, and identification of structures in the propagation space based on in situ data, remote-sensing observations, and simulations of the steady-state solar wind to complement our analysis. Results indicate that the changes observed in one ICME were likely caused by a stream interaction region, while the ICME exhibiting little change did not interact with any transients between Mercury and 1 au. This work provides an example of how interactions with corotating structures in the solar wind can induce fundamental changes in ICMEs. Our findings can help lay the foundation for improved predictions of ICME properties at 1 au.

Keywords: Corotating streams, Solar coronal mass ejections, Heliosphere
The Post-impact Evolution of the X-Ray-emitting Gas in SNR 1987A as Viewed by XMM-Newton. Since 1996 the blast wave driven by SN 1987A has been interacting with the dense circumstellar material, which provides us with a unique opportunity to study the early evolution of a newborn supernova remnant (SNR). Based on the XMM-Newton RGS and EPIC-pn X-ray observations from 2007 to 2019, we investigated the post-impact evolution of the X-ray-emitting gas in SNR 1987A. The hot plasma is represented by two nonequilibrium ionization components with temperatures of ~0.6 keV and ~2.5 keV. The low-temperature plasma has a density ~2400 cm-3, which is likely dominated by the lower-density gas inside the equatorial ring (ER). The high-temperature plasma with a density ~550 cm-3 could be dominated by the H II region and the high-latitude material beyond the ring. In the last few years, the emission measure of the low-temperature plasma has been decreasing, indicating that the blast wave has left the main ER. But the blast wave is still propagating into the high-latitude gas, resulting in the steady increase of the high-temperature emission measure. Meanwhile, the average abundances of N, O, Ne, and Mg are found to be declining, which may reflect the different chemical compositions between the two plasma components. We also detected Fe K lines in most of the observations, showing increasing flux and centroid energy. We interpret the Fe K lines as originating from a third hot component, which may come from the reflected shock heated gas or originate from Fe-rich ejecta clumps shocked by the reverse shock.

Keywords: Supernova remnants, Supernovae, X-ray astronomy, Interstellar medium
HInet: Generating Neutral Hydrogen from Dark Matter with Neural Networks. Upcoming 21 cm surveys will map the spatial distribution of cosmic neutral hydrogen (HI) over very large cosmological volumes. In order to maximize the scientific return of these surveys, accurate theoretical predictions are needed. Hydrodynamic simulations currently are the most accurate tool to provide those predictions in the mildly to nonlinear regime. Unfortunately, their computational cost is very high: tens of millions of CPU hours. We use convolutional neural networks to find the mapping between the spatial distribution of matter from N-body simulations and HI from the state-of-the-art hydrodynamic simulation IllustrisTNG. Our model performs better than the widely used theoretical model: halo occupation distribution for all statistical properties up to the nonlinear scales k ≲ 1 hr Mpc-1. Our method allows the generation of 21 cm mocks over very big cosmological volumes with similar properties to hydrodynamic simulations.

Keywords: Cosmology, Cosmological evolution, Large-scale structure of the universe, Neural networks, Convolutional neural networks, Observational cosmology
MIRKWOOD: Fast and Accurate SED Modeling Using Machine Learning. Traditional spectral energy distribution (SED) fitting codes used to derive galaxy physical properties are often uncertain at the factor of a few level owing to uncertainties in galaxy star formation histories and dust attenuation curves. Beyond this, Bayesian fitting (which is typically used in SED fitting software) is an intrinsically compute-intensive task, often requiring access to expensive hardware for long periods of time. To overcome these shortcomings, we have developed MIRKWOOD: a user-friendly tool comprising an ensemble of supervised machine-learning-based models capable of nonlinearly mapping galaxy fluxes to their properties. By stacking multiple models, we marginalize against any individual model's poor performance in a given region of the parameter space. We demonstrate MIRKWOOD's significantly improved performance over traditional techniques by training it on a combined data set of mock photometry of z = 0 galaxies from the SIMBA, EAGLE, and ILLUSTRISTNG cosmological simulations, and comparing the derived results with those obtained from traditional SED fitting techniques. MIRKWOOD is also able to account for uncertainties arising both from intrinsic noise in observations, and from finite training data and incorrect modeling assumptions. To increase the added value to the observational community, we use Shapley value explanations to fairly evaluate the relative importance of different bands to understand why particular predictions were reached. We envisage MIRKWOOD to be an evolving, open-source framework that will provide highly accurate physical properties from observations of galaxies as compared to traditional SED fitting.

Keywords: Extragalactic astronomy, Algorithms, Astronomy data analysis, Astrostatistics
Detection of <SUP>7</SUP>Be II in the Classical Nova V5669 Sgr (Nova Sagittarii 2015 No.3). We report the new detection of 7Be II in the ultraviolet spectra of V5669 Sgr during its early decline phase (+24 and +28 d). We identified three blueshifted absorption systems in our spectra. The first two, referred to as low- and high-velocity components, were noticeably identified among H I Balmer, Na I D, and Fe II whose lower energies of transients are low (&lt;4 eV). The third absorption component was identified among N II, He I, and C II lines whose lower energy levels are relatively high (9-21 eV). The absorption lines of 7Be II at 3130.583 Å and 3132.228 Å were identified as the first and second components in our observations. No evidence suggested the existence of Li I at 6708 Å in any velocity components. The estimated number density ratio of lithium relative to hydrogen, which was finally produced by this object using the equivalent widths of 7Be and Ca II K, $N{(}^{7}\mathrm{Li})/N{\left({\rm{H}}\right)}_{\mathrm{final}}$, is 4.0 ± 0.7 × 10-6. This value is an order of magnitude lower than the average observed values for classical novae wherein 7Be has been detected, and is comparable to the most optimistic value of theoretical predictions.

Keywords: High resolution spectroscopy, Galaxy chemical evolution, Nuclear abundances, Spectroscopy, Cataclysmic variable stars, Classical novae
The Core Mass Function across Galactic Environments. III. Massive Protoclusters. The stellar initial mass function (IMF) is fundamental for many areas of astrophysics, but its origin remains poorly understood. It may be inherited from the core mass function (CMF) or arise as a result of more chaotic, competitive accretion. Dense, gravitationally bound cores are seen in molecular clouds and some observations have suggested that the CMF is similar in shape to the IMF, though translated to higher masses by a factor of ~3. Here we measure the CMF in 28 dense clumps within 3.5 kpc that are likely to be central regions of massive protoclusters, observed via 1.3 mm dust continuum emission by the ALMAGAL project. We identify 222 cores using the dendrogram algorithm with masses ranging from 0.04 to 252 M☉. We apply completeness corrections for flux and number recovery, estimated from core insertion and recovery experiments. At higher masses, the final derived CMF is well described by a single power law of the form ${dN}/d\ \mathrm{log}\M\propto {M}^{-\alpha }$ with α ≃ 0.94 ± 0.08. However, we find evidence of a break in this power-law behavior between ~5 and 15 M☉, which is, to our knowledge, the first time such a break has been found in distant (≳1 kpc) regions by the Atacama Large Millimeter/submillimeter Array. We compare this massive protocluster CMF with those derived using the same methods in the G286 protocluster and a sample of infrared dark clouds. The massive protocluster CMF is significantly different, i.e., containing more massive cores, which is a potential indication of the role of environment on the CMF and IMF.

Keywords: Star formation, Interstellar medium
NOEMA Redshift Measurements of Extremely Bright Submillimeter Galaxies near the GOODS-N. We report spectroscopic redshift measurements for three bright submillimeter galaxies (SMGs) near the GOODS-N field, each with SCUBA-2 850 μm fluxes &gt;10 mJy, using the Northern Extended Millimeter Array (NOEMA). Our molecular line-scan observations of these sources, which occupy an ~7 arcmin2 area outside of the Hubble Space Telescope coverage of the field, reveal that two lie at z ~ 3.14. In the remaining object, we detect line emission consistent with CO(7-6), [C I], and H2O at z = 4.42. The far-infrared spectral energy distributions of these galaxies, constrained by SCUBA-2, NOEMA, and Herschel/SPIRE, indicate instantaneous star formation rates ~4000 M☉ yr-1 in the z = 4.42 galaxy and ~2500 M☉ yr-1 in the two z ~ 3.14 galaxies. Based on the sources' CO line luminosities, we estimate Mgas ~ 1011M☉ and find gas depletion timescales of τdepl ~ 50 Myr, consistent with findings in other high-redshift SMGs. Finally, we show that the two z ~ 3.14 sources, which alone occupy a volume ~10 Mpc3, very likely mark the location of a protocluster of bright SMGs and less-dusty optical sources.

Keywords: Submillimeter astronomy, Galaxy evolution, CO line emission, High-redshift galaxy clusters
GECKO Optical Follow-up Observation of Three Binary Black Hole Merger Events: GW190408_181802, GW190412, and GW190503_185404. We present optical follow-up observation results of three binary black hole merger (BBH) events, GW190408_181802, GW190412, and GW190503_185404, which were detected by the Advanced LIGO and Virgo gravitational wave (GW) detectors. Electromagnetic (EM) counterparts are generally not expected for BBH merger events. However, some theoretical models suggest that EM counterparts of BBH can possibly arise in special environments, prompting motivation to search for EM counterparts for such events. We observed high-credibility regions of the sky for the three BBH merger events with telescopes of the Gravitational-wave EM Counterpart Korean Observatory (GECKO), including the KMTNet. Our observation started as soon as 100 minutes after the GW event alerts and covered 29-63 deg2 for each event with a depth of ~22.5 mag in the R band within hours of observation. No plausible EM counterparts were found for these events, but based on there being no detection of the GW190503_185404 event, for which we covered the 69% credibility region, we place the BBH merger EM counterpart signal to be Mg &gt; - 18.0 AB mag within about one day of the GW event. The comparison of our detection limits with light curves of several kilonova models suggests that a kilonova event could have been identified within hours of the GW alert with GECKO observations if the compact merger happened at &lt;400 Mpc and the localization accuracy was on the order of 50 deg2. Our result shows great promise for the GECKO facilities to find EM counterparts within a few hours from GW detection in future GW observation runs.

Keywords: Black holes, High energy astrophysics, Optical identification, Compact binary stars, Stellar mass black holes, Gravitational wave sources, Novae, Gravitational wave astronomy, Gravitational waves, Time domain astronomy, Compact objects, Time series analysis
Accretion onto Stars in the Disks of Active Galactic Nuclei. Disks of gas accreting onto supermassive black holes are thought to power active galactic nuclei (AGN). Stars may form in gravitationally unstable regions of these disks, or may be captured from nuclear star clusters. Because of the dense gas environment, the evolution of these embedded stars can diverge dramatically from those in the interstellar medium. This work extends previous studies of stellar evolution in AGN disks by exploring a variety of ways in which accretion onto stars in AGN disks may differ from Bondi accretion. We find that tidal effects from the supermassive black hole significantly alter the evolution of stars in AGN disks, and that our results do not depend critically on assumptions about radiative feedback on the accretion stream. Thus, in addition to depending on the ambient density and sound speed, the fate of stars in AGN disks depends sensitively on the distance to and mass of the supermassive black hole. This affects the location in the disk in which stellar explosions occur, where compact remnants form and potentially merge to produce gravitational waves, and where different types of chemical enrichment take place.

Keywords: Stellar physics, Galactic center, Stellar evolutionary models, Quasars
General Exact Law of Compressible Isentropic Magnetohydrodynamic Flows: Theory and Spacecraft Observations in the Solar Wind. Various forms of exact laws governing magnetohydrodynamic (MHD) turbulence have been derived either in the incompressibility limit, or for isothermal compressible flows. Here we propose a more general method that allows us to obtain such laws for any turbulent isentropic flow (i.e., constant entropy). We demonstrate that the known MHD exact laws (incompressible and isothermal) and the new (polytropic) one can be obtained as specific cases of the general law when the corresponding closure equation is stated. We also recover all known exact laws of hydrodynamic (HD) turbulence (incompressible, isothermal, and polytropic) from this law in the limit B = 0. We furthermore show that the difference between the two forms (isothermal and polytropic) of the MHD exact laws of interest in this work resides in some of the source terms and in the explicit form of the flux term that depends on internal energy. Finally, we apply these two forms to Parker Solar Probe data taken in the inner heliosphere to highlight how the different closure equations affect the energy cascade rate estimates.

Keywords: Magnetohydrodynamics, Plasma physics, Interplanetary turbulence, Solar wind, Plasma astrophysics, Solar physics
Spatial Variation in Strong Line Ratios and Physical Conditions in Two Strongly Lensed Galaxies at z 1.4. Upcoming space-based integral field spectrographs will enable spatially resolved spectroscopy of distant galaxies, including at the scale of individual star-forming regions (i.e., down to just tens of parsecs) in galaxies that have been strongly gravitationally lensed. In the meantime, there is only a very small set of lensed galaxies where such spatial detail is possible at wavelengths containing important rest-optical emission lines, even with the Hubble Space Telescope's Wide Field Camera 3 infrared channel grisms. Here, we examine two of these sources, SDSS J1723+3411 and SDSS J2340+2947, using HST WFC3/IR grism data and supporting spatially unresolved spectroscopy from several ground-based instruments to explore the size of spatial variations in observed strong emission-line ratios like O32 and R23, which are sensitive to ionization parameter and metallicity, and the Balmer decrement, which is an indicator of reddening. We find significant spatial variation in the reddening and in the reddening-corrected O32 and R23 values that correspond to spreads of a few tenths of a dex in ionization parameter and metallicity. We also find clear evidence of a negative radial gradient in star formation in SDSS J2340+2947 and tentative evidence of one in SDSS J1723+3411, though its star formation is quite asymmetric. Finally, we find that reddening can vary enough spatially to make spatially resolved reddening corrections necessary in order to characterize gradients in line ratios and the physical conditions inferred from them, necessitating the use of space-based integral field units for future work on larger, more statistically robust samples.

Keywords: Galaxy properties, Strong gravitational lensing, High-redshift galaxies, Interstellar medium
Limits on Millimeter Continuum Emission from Circumplanetary Material in the DSHARP Disks. We present a detailed analysis for a subset of the high-resolution (~35 mas, or 5 au) ALMA observations from the Disk Substructures at High Angular Resolution Project (DSHARP) to search for faint 1.3 mm continuum emission associated with dusty circumplanetary material located within the narrow annuli of depleted emission (gaps) in circumstellar disks. This search used the Jennings et al. frank modeling methodology to mitigate contamination from the local disk emission and then deployed a suite of injection-recovery experiments to statistically characterize point-like circumplanetary disks in residual images. While there are a few putative candidates in this sample, they have only marginal local signal-to-noise ratios and would require deeper measurements to confirm. Associating a 50% recovery fraction with an upper limit, we find that these data are sensitive to circumplanetary disks with flux densities ≳50-70 μJy in most cases. There are a few examples where those limits are inflated (≳110 μJy) owing to lingering nonaxisymmetric structures in their host circumstellar disks, most notably for a newly identified faint spiral in the HD 143006 disk. For standard assumptions, this analysis suggests that these data should be sensitive to circumplanetary disks with dust masses $\gtrsim 0.001\mbox{--}0.2\,{M}_{\oplus }$. While those bounds are comparable to some theoretical expectations for young giant planets, we discuss how plausible system properties (e.g., relatively low host planet masses or the efficient radial drift of solids) could require much deeper observations to achieve robust detections.

Keywords: Exoplanet formation, Planetary-disk interactions, Protoplanetary disks, Planet formation
Uniform Forward-modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking. We present a forward-modeling framework using the Bayesian inference tool Starfish and cloudless Sonora-Bobcat model atmospheres to analyze low-resolution (R ≈ 80-250) near-infrared (1.0-2.5 μm) spectra of T dwarfs. Our approach infers effective temperatures, surface gravities, metallicities, radii, and masses, and by accounting for uncertainties from model interpolation and correlated residuals due to instrumental effects and modeling systematics, produces more realistic parameter posteriors than traditional (χ2-based) spectral-fitting analyses. We validate our framework by fitting the model atmospheres themselves and finding negligible offsets between derived and input parameters. We apply our methodology to three well-known benchmark late-T dwarfs, HD 3651B, GJ 570D, and Ross 458C, using both solar and nonsolar metallicity atmospheric models. We also derive these benchmarks' physical properties using their bolometric luminosities, their primary stars' ages and metallicities, and Sonora-Bobcat evolutionary models. Assuming the evolutionary-based parameters are more robust, we find our atmospheric-based, forward-modeling analysis produces two outcomes. For HD 3615B and GJ 570D, spectral fits provide accurate Teff and R but underestimated $\mathrm{log}g$ (by ≈1.2 dex) and Z (by ≈0.35 dex), likely due to the systematics from modeling the potassium line profiles. For Ross 458C, spectral fits provide accurate $\mathrm{log}g$ and Z but overestimated Teff (by ≈120 K) and underestimated R (by ≈1.6×), likely because our model atmospheres lack clouds, reduced vertical temperature gradients, or disequilibrium processes. Finally, the spectroscopically inferred masses of these benchmarks are all considerably underestimated.

Keywords: Stellar atmospheres, Brown dwarfs, Exoplanet atmospheres, T dwarfs
Multimessenger Detection Rates and Distributions of Binary Neutron Star Mergers and Their Cosmological Implications. Gravitational wave (GW) events, produced by the coalescence of binary neutron stars (BNSs), can be treated as the standard sirens to probe the expansion history of the universe, if their redshifts can be determined from electromagnetic (EM) observations. For the high-redshift (z ≳ 0.1) events, the short γ-ray bursts (sGRBs) and the afterglows are always considered as the primary EM counterparts. In this paper, by investigating various models of sGRBs and afterglows, we discuss the rates and distributions of the multimessenger observations of BNS mergers using GW detectors in the second-generation (2G), 2.5G, and 3G era with detectable sGRBs and afterglows. For instance, for the Cosmic Explorer GW detector, the rate is about 300-3500 yr-1 with a GECAM-like detector for γ-ray emissions and an LSST/WFST detector for optical afterglows. In addition, we find that these events have redshifts z ≲ 2 and inclination angles ι ≲ 20°. These results justify the rough estimation in previous works. Considering these events as standard sirens to constrain the equation-of-state parameters of dark energy w0 and wa, we obtain the potential constraints of Δw0 ≃ 0.02-0.05 and Δwa ≃ 0.1-0.4.

Keywords: Gamma-ray bursts, Gravitational waves, Dark energy
Revisiting Dynamical Friction: The Role of Global Modes and Local Wakes. The orbital decay of a perturber within a larger system plays a key role in the dynamics of many astrophysical systems-from nuclear star clusters or globular clusters in galaxies, to massive black holes in galactic nuclei, to dwarf galaxy satellites within the dark matter halos of more massive galaxies. For many decades, there have been various attempts to determine the underlying physics and timescales of the drag mechanism, ranging from the local dynamical friction approach to descriptions based on the back-reaction of global modes induced in the background system. We present ultra-high-resolution N-body simulations of massive satellites orbiting a Milky Way-like galaxy (with &gt; 108 particles), that appear to capture both the local "wake" and the global "mode" induced in the primary halo. We address directly the mechanism of orbital decay from the combined action of local and global perturbations and specifically analyze where the bulk of the torque originates.

Keywords: Milky Way Galaxy, Galaxy dynamics, Dwarf galaxies, Galaxy interactions, Galaxy kinematics, Dynamical friction, Dark matter, Galaxies