Sazuna/UAT_keywords huggingface dataset:
Low-temperature Formation of Carbonaceous Dust Grains from PAHs. Carbon is ubiquitous in space and plays a key role in prebiotic chemistry. Astronomical observations have found interstellar carbon in the form of polycyclic aromatic hydrocarbons (PAHs) as well as carbonaceous dust, confirming its presence in both gaseous and solid phases. The goal of this study is to experimentally investigate low-temperature chemical pathways between these two phases in order to better understand the evolution of cosmic carbon. Cosmic dust analogs are produced in the supersonic expansion of an argon jet seeded with aromatic molecules: benzene, naphthalene, anthracene, phenanthrene, and pyrene. These are prototype aromatic molecules of compact and noncompact structure, and are used to evaluate the effect of precursor structure on the molecular complexity of the resulting grains. The seeded jet is exposed to an electrical discharge and the carbonaceous grains are collected and probed ex situ via laser desorption mass spectrometry. Mass spectra reveal a rich molecular diversity within the grains, including fragments of the parent molecule but also growth into larger complex organic molecules (COMs). In all experiments, the largest number of products is found in the m/z range 200-250, and C16H10 (attributed to pyrene and/or its isomers) is found to be a dominant product, pointing at the formation of this stable PAH as a preferential route in the growth to larger PAHs. Comparison to mass spectra from the Murchison meteorite reveals a similar dominance of compounds related to C16H10 at m/z = 202. Evidence of the methyl-addition-cyclization mechanism in the anthracene experiment is reported. PAH structure is found to impact the dust production yield, as seen by the greater yield for the anthracene compared to the phenanthrene experiment. PAH growth at low temperatures via barrierless routes involving the addition of alkyl- and phenyl-type radicals is suggested as a viable pathway to COMs. These results suggest that PAH growth and dust formation from PAHs are feasible at low temperatures in photon-dominated regions and circumstellar envelopes.

Keywords: Interstellar molecules, Interstellar dust, Polycyclic aromatic hydrocarbons, Laboratory astrophysics, Astrochemistry
NuSTAR Observations and Multiwavelength Modeling of the High-redshift BL Lacertae Object 4FGL J2146.5-1344. High synchrotron peak (HSP; ${\nu }_{\mathrm{sy}}^{\mathrm{pk}}\gt {10}^{15}$ Hz) BL Lac objects are some of the most extreme accelerators in the universe. Those found at high redshifts (z &gt; 1) challenge our understanding of blazar evolution models and are crucial for cosmological measurements of the extragalactic background light. In this paper, we study a high-z BL Lac object, 4FGL J2146.5-1344, detected to be at z = 1.34 using the photometric dropout technique. We collected multiwavelength data for this source from optical up to γ-rays, in order to study its spectral energy distribution (SED). In particular, this source was observed for the first time with the Nuclear Spectroscopic Telescope Array, which accurately measures the synchrotron emission of this blazar up to 50 keV. Despite being classified as an HSP BL Lac object, the modeling of the SED reveals that this source likely belongs to the "masquerading BL Lac" class, which comprises flat spectrum radio quasars appearing as disguised BL Lac objects.

Keywords: Astronomy data modeling, BL Lacertae objects, Blazars, Active galaxies, Active galactic nuclei, High-redshift galaxies
The CO(3-2)/CO(1-0) Luminosity Line Ratio in Nearby Star-forming Galaxies and Active Galactic Nuclei from xCOLD GASS, BASS, and SLUGS. We study the ${r}_{31}={L}_{\mathrm{CO}(3\mbox{--}2)}^{{\prime} }/{L}_{\mathrm{CO}(1\mbox{--}0)}^{{\prime} }$ luminosity line ratio in a sample of nearby (z &lt; 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS survey, 36 hard X-ray-selected active galactic nucleus (AGN) host galaxies from the BAT AGN Spectroscopic Survey, and 37 infrared-luminous galaxies from the SCUBA Local Universe Galaxy Survey. We find a trend for r31 to increase with star formation efficiency (SFE). We model r31 using the UCL-PDR code and find that the gas density is the main parameter responsible for the variation of r31, while the interstellar radiation field and cosmic-ray ionization rate play only a minor role. We interpret these results to indicate a relation between SFE and gas density. We do not find a difference in the r31 value of SFGs and AGN host galaxies, when the galaxies are matched in SSFR (&lt;r31&gt; = 0.52 ± 0.04 for SFGs and &lt;r31&gt; = 0.53 ± 0.06 for AGN hosts). According to the results of the UCL-PDR models, the X-rays can contribute to the enhancement of the CO line ratio, but only for strong X-ray fluxes and for high gas density (nH &gt; 104 cm-3). We find a mild tightening of the Kennicutt-Schmidt relation when we use the molecular gas mass surface density traced by CO(3-2) (Pearson correlation coefficient R = 0.83), instead of the molecular gas mass surface density traced by CO(1-0) (R = 0.78), but the increase in correlation is not statistically significant (p-value = 0.06). This suggests that the CO(3-2) line can be reliably used to study the relation between SFR and molecular gas for normal SFGs at high redshift and to compare it with studies of low-redshift galaxies, as is common practice.

Keywords: Seyfert galaxies, Active galactic nuclei, Star formation, Interstellar medium, Galaxies
A Study of the Observational Properties of Coronal Mass Ejection Flux Ropes near the Sun. We present the observational properties of coronal mass ejection (CME) flux ropes (FRs) near the Sun based on a set of 35 events from solar cycle 24 (2010-2017). We derived the CME FR properties using the Flux Rope from Eruption Data technique. According to this technique, the geometrical properties are obtained from a flux-rope fit to CMEs and the magnetic properties from the reconnected flux in the source region. In addition, we use the magnetic flux in the dimming region at the eruption site. Geometric properties like radius of the FR and the aspect ratio are derived from the FR fitting. The reconnected flux exhibits a positive correlation with flare fluence in soft X-rays (SXRs), peak flare intensity in SXRs, CME speed, and kinetic energy, with correlation coefficients (cc) 0.78, 0.6, 0.48, and 0.55, respectively. We found a moderate positive correlation between magnetic flux in the core dimming regions and the toroidal flux obtained from the Lundquist solution for a force-free FR (cc = 0.43). Furthermore, we correlate the core dimming flux and CME mass (cc = 0.34). The area of the core dimming region shows a moderate correlation with the radius of the FR (cc = 0.4). Thus, we infer that greater magnetic content (poloidal and toroidal fluxes) indicates a more energetic eruption in terms of flare size, CME speed, kinetic energy, mass, and radius of the FR, suggesting important implications for space weather predictions.

Keywords: Solar coronal mass ejections, Solar magnetic reconnection, Solar x-ray flares
Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A Measurement of Circular Polarization at 40 GHz. We report measurements of circular polarization from the first two years of observation with the 40 GHz polarimeter of the Cosmology Large Angular Scale Surveyor (CLASS). CLASS is conducting a multi-frequency survey covering 75% of the sky from the Atacama Desert designed to measure the cosmic microwave background (CMB) linear E and B polarization on angular scales 1° ≲ θ ≤ 90°, corresponding to a multipole range of 2 ≤ ℓ ≲ 200. The modulation technology enabling measurements of linear polarization at the largest angular scales from the ground, the Variable-delay Polarization Modulator, is uniquely designed to provide explicit sensitivity to circular polarization (Stokes V). We present a first detection of circularly polarized atmospheric emission at 40 GHz that is well described by a dipole with an amplitude of $124\pm 4\,\mu {\rm{K}}$ when observed at an elevation of 45°, and discuss its potential impact on the recovery of linear polarization by CLASS. Filtering the atmospheric component, CLASS places a 95% confidence upper limit of $0.4\,\mu {{\rm{K}}}^{2}$ to $13.5\,\mu {{\rm{K}}}^{2}$ on ${\ell }({\ell }+1){C}_{{\ell }}^{{VV}}/(2\pi )$ for $1\leqslant {\ell }\leqslant 120$ , representing an improvement by two orders of magnitude over previous CMB limits.

Keywords: Early universe, Sky surveys, Big Bang theory, Cosmic microwave background radiation, Observational cosmology, Astronomical instrumentation, Polarimeters, Reionization
Triggering Mechanism and Material Transfer of a Failed Solar Filament Eruption. Solar filament eruptions are often associated with solar flares and coronal mass ejections, which have the greatest impact on space weather. However, the fine structures and the trigger mechanisms of solar filaments are still unclear. To address these issues, we studied a failed solar active-region filament eruption associated with a C-class flare by using high-resolution Hα images from the New Vacuum Solar Telescope, supplemented by EUV observations from the Solar Dynamics Observatory. Before the filament eruption, a small bipolar magnetic field emerged below the filament. Then magnetic reconnection between the filament and the emerging bipolar magnetic field triggered the filament eruption. During the filament eruption, the untwisting motion of the filament can be clearly traced by the eruptive threads. Moreover, the footpoints of the eruptive threads are determined by tracing the descending filament material. Note that the twisted structure of the filament and the right part of the eruptive filament threads cannot be seen before the filament eruption. These eruptive threads in the right part of the filament are found to be rooting in the weak negative polarities near the main negative sunspot. Moreover, a new filament formed in the filament channel due to material injection from the eruptive filament. The above observations and the potential field extrapolations are inclined to support the idea that the filament materials were transferred into the overlying magnetic loops and the nearby filament channel by magnetic reconnection. These observations improve our understanding of the complexity of filament eruptions.

Keywords: Solar active region magnetic fields, Solar atmosphere, Solar flares, Solar magnetic reconnection, Solar active region filaments, Sunspots, Solar physics, Solar magnetic fields, Solar filament eruptions, Solar activity
The Density Structure of Simulated Stellar Streams. Star particles in a set of dense clusters are self-consistently evolved within an LCDM dark matter distribution with an n-body code. The clusters are started on nearly circular orbits in the more massive sub-halos. Each cluster develops a stellar tidal stream, initially within its original sub-halo. When a sub-halo merges into the main halo the early time stream is dispersed as a somewhat chaotic thick stream, roughly the width of the orbit of the cluster in the sub-halo. Once the cluster orbits freely in the main halo the star stream forms a thin stream again, usually resulting in a thin stream surrounded by a wider distribution of star particles lost at earlier times. To examine the role of the lower-mass dark matter sub-halos in the creation of density variations along the thin tidal star streams two realizations of the simulation are run with and without a normal cold dark matter sub-halo population below 4 × 108 $\,{M}_{\odot }$ . About 70(40)% of thin streams show density variations that are 2(5) times the star count noise level, irrespective of the presence or absence of low-mass sub-halos. A counts-in-cells analysis (related to the two-point correlation function and power spectrum) of the density along nearly 8000° of streams in the two well matched models finds that the full sub-halo population leads to slightly larger, but statistically significant, density fluctuations on scales of 2°-6°.

Keywords: Globular star clusters, Milky Way dark matter halo, Tidal tails, Milky Way stellar halo, N-body simulations
The Impact of Metallicity on the Evolution of the Rotation and Magnetic Activity of Sun-like Stars. The rotation rates and magnetic activity of Sun-like and low-mass (≲1.4M⊙) main-sequence stars are known to decline with time, and there now exist several models for the evolution of rotation and activity. However, the role that chemical composition plays during stellar spin-down has not yet been explored. In this work, we use a structural evolution code to compute the rotational evolution of stars with three different masses (0.7, 1.0, and 1.3 M⊙) and six different metallicities, ranging from [Fe/H] = -1.0 to [Fe/H] = +0.5. We also implement three different wind-braking formulations from the literature (two modern and one classical) and compare their predictions for rotational evolution. The effect that metallicity has on stellar structural properties, and in particular the convective turnover timescale, leads the two modern wind-braking formulations to predict a strong dependence of the torque on metallicity. Consequently, they predict that metal-rich stars spin down more effectively at late ages (≳1 Gyr) than metal-poor stars, and the effect is large enough to be detectable with current observing facilities. For example, the formulations predict that a Sun-like (solar-mass and solar-aged) star with [Fe/H] = -0.3 will have a rotation period of less than 20 days. Even though old, metal-poor stars are predicted to rotate more rapidly at a given age, they have larger Rossby numbers and are thus expected to have lower magnetic activity levels. Finally, the different wind-braking formulations predict quantitative differences in the metallicity dependence of stellar rotation, which may be used to test them.

Keywords: Stellar rotation, Metallicity, Stellar activity, Stellar evolution
Using Multi-line Spectropolarimetric Observations of Forbidden Emission Lines to Measure Single-point Coronal Magnetic Fields. Polarized magnetic dipole (M1) emission lines provide important diagnostics for the magnetic field dominating the evolution of the solar corona. This paper advances a multi-line technique using specific combinations of M1 lines to infer the full vector magnetic field for regions of optically thin emission that can be localized along a given line of sight. Our analytical formalism is a generalization of the "single-point inversion" approach introduced by Plowman. We show that combinations of M1 transitions for which each is either a $J=1\to 0$ transition or has equal Landé g-factors for the upper and lower levels contain degenerate spectropolarimetric information that prohibits the application of the single-point inversion technique. This may include the pair of Fe XIII lines discussed by Plowman. We identify the Fe XIII 10747 Å and Si X 14301 Å lines as one alternative combination for implementing this technique. Our sensitivity analysis, based on coronal loop properties, suggests that for photon noise levels around 10-4 of the line intensity, which will be achievable with the National Science Foundation's Daniel K. Inouye Solar Telescope, magnetic fields with sufficient strength (∼10 G) and not severely inclined to the line of sight (≲35°) can be recovered with this method. Degenerate solutions exist, though we discuss how added constraints may help resolve them or reduce their number.

Keywords: Solar coronal lines, Solar coronal loops, Spectropolarimetry, Solar magnetic fields
Systematic Study of the Peak Energy of Broadband Gamma-Ray Burst Spectra. We have performed a systematic study of gamma-ray bursts (GRBs), which have various values in the peak energy of the νFν spectrum of prompt emission, Epeak, observed by the Swift/Burst Alert Telescope (BAT) and Fermi/Gamma-ray Burst Monitor, investigating their prompt and X-ray afterglow emissions. We cataloged long-lasting GRBs observed by Swift between 2004 December and 2014 February in three categories according to the classification by Sakamoto et al.: X-ray flashes (XRFs), X-ray-rich GRBs (XRRs), and classical GRBs (C-GRBs). We then derived ${E}_{\mathrm{peak}}^{\mathrm{obs}}$ , as well as ${E}_{\mathrm{peak}}^{\mathrm{src}}$ if viable, of the Swift spectra of their prompt emission. We also analyzed their X-ray afterglows and found that GRB events with a lower ${E}_{\mathrm{peak}}^{\mathrm{src}}$ , I.e., softer GRBs, are fainter in 0.3-10 keV X-ray luminosity and decay more slowly than harder GRBs. The intrinsic event rates of the XRFs, XRRs, and C-GRBs were calculated using the Swift/BAT trigger algorithm. Those of the XRRs and XRFs are larger than that of the C-GRBs. If we assume that the observational diversity of Epeak is explained using the off-axis model, these results yield a jet half-opening angle of Δθ ∼ 0°3, and a variance of the observing angles θobs ≲ 0°6. This implies that this tiny variance would be responsible for the Epeak diversity observed by Swift/BAT, which is unrealistic. Therefore, we conclude that the Epeak diversity is not explained with the off-axis model, but is likely to originate from some intrinsic properties of the jets.

Keywords: Gamma-ray bursts, Jets, Relativistic jets, High energy astrophysics
The Polarization of X-Rays from Warped Black Hole Accretion Disks. It is commonly assumed that in black hole (BH) accretion disks the angular momenta of the disk and the BH are aligned. However, for a significant fraction of stellar-mass BHs and supermassive BHs, the momenta may not be aligned. In such systems, the interplay of disk viscosity and general relativistic frame dragging can cause the disk to warp or break into two (or more) distinct planes; this is called the Bardeen-Petterson effect. We have developed a general relativistic ray-tracing code to find the energy spectra and polarization of warped accretion disks, accounting for the emission from the disk and for photons reflecting one or multiple times off the warped accretion disk segments. We find that polarization angle can be used to give a lower limit on the misalignment angle when a previous measurement of the jet, which is thought be aligned with the BH angular momentum, can be spatially resolved.

Keywords: High energy astrophysics, Polarimetry, Black holes, Relativistic disks
Understanding the Structure of Rapid Intensity Fluctuations in the Chromosphere with IRIS. Several recent data sets have taken advantage of the unique capabilities of orbital and suborbital spacecraft to image the chromosphere and transition region at a very high cadence. We find that both the chromosphere and transition region exhibit spatially coherent transient features at frequencies above 80 mHz. We have analyzed narrowband imaging data from H I Lyα 1215 Å (provided by CLASP), Mg II k 2796 Å, and Si IV 1400 Å (provided by the Interface Region Imaging Spectrograph). We categorize the spatial structure of these rapid fluctuations in different magnetic environments. Intensity fluctuations above the noise level are observed in plages in all passbands. We have found jet-like features in 1215 and 1400 Å data that extend from the edges of plages as well as network magnetic concentrations. We have not found any recurrent features that are identified in both 1400 and 1215 Å data. Short loop-like features were only found in 1400 Å data. Temperature minimum grains generate non-propagating features in 1400 Å data. We compare our observations with previous research on dynamic chromospheric phenomena at lower frequencies. Candidate mechanisms, related to both jets and waves, predict chromospheric and transition region intensity fluctuations at high temporal frequencies, which can now be observationally probed.

Keywords: Solar oscillations, Solar chromosphere, Solar transition region
Introducing the Search for Intermediate-mass Black Holes in Nearby Galaxies (SIBLING) Survey. Intermediate-mass black holes (IMBHs) have masses between 102 and 106 M⊙ and are key to our understanding of the formation of massive black holes. The known population of IMBHs remains small, with a few hundred candidates and only a handful of them confirmed as bona fide IMBHs. Until now, the most widely used selection method is based on spectral analysis. Here we present a methodology to select IMBH candidates via optical variability analysis of the nuclear region of local galaxies ( $z\leqslant 0.35$ ). Active IMBHs accreting at low rates show small amplitude variability with timescales of hours, as is seen in one of the known IMBHs, NGC 4395. We found a sample of ∼500 galaxies demonstrating fast and small amplitude variation in their week-based light curves. We estimate an average occupancy fraction of 4% and a surface density of ∼3 deg-2, which represent an increase by a factor of ∼40 compared to previous searches. A large fraction (78%) of the candidates are in spiral galaxies. We preliminarily confirm the active galactic nucleus nature of 22 sources via Baldwin, Phillips, and Terlevich diagrams using Sloan Digital Sky Survey legacy spectra. Further confirmation of these candidates will require multiwavelength observations, especially in X-ray and radio bands.

Keywords: AGN host galaxies, Intermediate-mass black holes, Surveys, Active galaxies, Galaxy counts, Galaxies
Circumbinary Accretion from Finite and Infinite Disks. We carry out 2D viscous hydrodynamics simulations of circumbinary disk (CBD) accretion using AREPO. We resolve the accretion flow from a large-scale CBD down to the streamers and disks around individual binary components. Extending our recent studies, we consider circular binaries with various mass ratios (0.1 ≤ qb ≤ 1) and study accretion from "infinite," steady-supply disks and from finite-sized, viscously spreading tori. For "infinite" disks, a global steady state can be reached, and the accretion variability has a dominant frequency ∼0.2Ωb for qb &gt; 0.5 and Ωb for qb &lt; 0.5 (Ωb is the binary angular frequency). We find that the accretion "eigenvalue" l0—the net angular momentum transfer from the disk to the binary per unit accreted mass—is always positive and falls in the range (0.65- $0.85){a}_{{\rm{b}}}^{2}{{\rm{\Omega }}}_{{\rm{b}}}$ (with ab the binary separation), depending weakly on the mass ratio and viscosity. This leads to binary expansion when qb ≳ 0.3. Accretion from a finite torus can be separated into two phases: an initial transient phase, corresponding to the filling of the binary cavity, followed by a viscous pseudostationary phase, during which the torus viscously spreads and accretes onto the binary. In the viscous phase, the net torque on the binary per unit accreted mass is close to l0, the value derived for "infinite" disks. We conclude that binaries of similar mass accreting from CBDs gain angular momentum and expand over long timescales. This result significantly impacts the coalescence of supermassive binary black holes and newly formed binary stars. We offer a word of caution against conclusions drawn from simulations of transient accretion onto empty circumbinary cavities.

Keywords: Black hole physics, Supermassive black holes, Binary stars, Orbital evolution, Gravitational wave sources, Star formation, Stellar accretion disks