Sazuna/UAT_keywords huggingface dataset:
The Gas-Star Formation Cycle in Nearby Star-forming Galaxies. I. Assessment of Multi-scale Variations. The processes regulating star formation in galaxies are thought to act across a hierarchy of spatial scales. To connect extragalactic star formation relations from global and kiloparsec-scale measurements to recent cloud-scale resolution studies, we have developed a simple, robust method that quantifies the scale dependence of the relative spatial distributions of molecular gas and recent star formation. In this paper, we apply this method to eight galaxies with ∼1″ resolution molecular gas imaging from the Physics at High Angular resolution in Nearby GalaxieS-ALMA (PHANGS-ALMA) survey and PdBI Arcsecond Whirlpool Survey (PAWS) that have matched resolution, high-quality narrowband Hα imaging. At a common scale of 140 pc, our massive (log(M ⋆[M ☉]) = 9.3-10.7), normally star-forming (SFR[M ☉ yr-1] = 0.3-5.9) galaxies exhibit a significant reservoir of quiescent molecular gas not associated with star formation as traced by Hα emission. Galactic structures act as backbones for both molecular gas and H II region distributions. As we degrade the spatial resolution, the quiescent molecular gas disappears, with the most rapid changes occurring for resolutions up to ∼0.5 kpc. As the resolution becomes poorer, the morphological features become indistinct for spatial scales larger than ∼1 kpc. The method is a promising tool to search for relationships between the quiescent or star-forming molecular reservoir and galaxy properties, but requires a larger sample size to identify robust correlations between the star-forming molecular gas fraction and global galaxy parameters.

Keywords: Interstellar medium, Galaxies
Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather. The paper investigates the capability of geomagnetic storm parameters in the disturbance storm-time (Dst), Kp, and AE indices to distinguish between severe space weather (SvSW) that causes the reported electric power outages and/or telecommunication failures and normal space weather (NSW) that does not cause these severe effects in a 50 yr period (1958-2007). The parameters include the storm intensities DstMin (minimum Dst during the main phase, MP, of the storm), (dDst/dt)MPmax, Kpmax, and AEmax. In addition, the impulsive parameter {IpsDst}=(-1/{T}MP}){\int }TMP}| {Dst}}MP}| {dt} is derived for the storms that are automatically identified in the Kyoto Dst and USGS {Dst}.{\int }TMP}| {Dst}}MP}| {dt} is the integral of the modulus of the Dst from onset of the MP (MPO) to the DstMin. T MP is the MP duration from MPO to DstMin. The corresponding mean values &lt; {Kp}}MP}&gt; and &lt; {AE}}MP}&gt; are also calculated. Regardless of the significant differences in the storm parameters between the two Dst indices, the IpsDst in both indices seems to identify four of the five SvSW events (and the Carrington event) in more than 750 NSW events that have been reported to have occurred in 1958-2007, while all other parameters separate one or two SvSWs from the NSWs. Using the Kyoto IpsDst threshold of -250 nT, we demonstrate a 100% true SvSW identification rate with only one false NSW. Using the false NSW event (1972 August 4), we investigate whether using a higher resolution Dst might result in a more accurate identification of SvSWs. The mechanism of the impulsive action leading to large IpsDst and SvSW involves the coincidence that the fast interplanetary coronal mass ejection velocity V contains its shock (or front) velocity \bigtriangleup V and large interplanetary magnetic field Bz southward covering \bigtriangleup V.

Keywords: Space weather, Solar wind, Geomagnetic fields
Detecting the 21 cm Signal from the Epoch of Reionization Using Drift Scans: Correlation of Time-ordered Visibilities. We present a formalism to extract the H I power spectrum from the epoch of reionization for drift scans using radio interferometers. Our main aim is to determine the coherence timescale of time-ordered visibilities. We compute the two-point correlation function of the H I visibilities measured at different times to address this question. We determine, for a given baseline, the decorrelation of the amplitude and the phase of this complex function. Our analysis uses primary beams of four ongoing and future interferometers—Precision Array for Probing the Epoch of Reionization, Murchison Widefield Array, Hydrogen Epoch of Reionization Array, and Square Kilometre Array (SKA1-Low). We identify physical processes responsible for the decorrelation of the H I signal and isolate their impact by making suitable analytic approximations. The decorrelation timescale of the amplitude of the correlation function lies in the range of 2-20 minutes for baselines of interest for the extraction of the H I signal. The phase of the correlation function can be made small after scaling out an appropriate term, which also causes the coherence timescale of the phase to be longer than the amplitude of the correlation function. We find that our results are insensitive to the input H I power spectrum, and therefore, they are directly applicable to the analysis of the drift scan data. We also apply our formalism to a set of point sources and statistically homogeneous diffuse correlated foregrounds. We find that point sources decorrelate on a timescale much shorter than the H I signal. This provides a novel mechanism to partially mitigate the foregrounds in a drift scan.

Keywords: Cosmology, Early universe, Radio astronomy, Observational cosmology, Astronomical techniques, Interferometric correlation, Drift scan imaging, Reionization, Radio interferometry, Nonclassical interferometry, Astronomical methods
Mind the Gap: The Location of the Lower Edge of the Pair-instability Supernova Black Hole Mass Gap. Detections of gravitational waves are now starting to probe the mass distribution of stellar mass black holes (BHs). Robust predictions from stellar models are needed to interpret these. Theory predicts the existence of a gap in the BH mass distribution because of pair-instability supernovae. The maximum BH mass below the gap is the result of pulsational mass loss. We evolve massive helium stars through their late hydrodynamical phases of evolution using the open-source MESA stellar evolution code. We find that the location of the lower edge of the mass gap at 45 {M}⊙  is remarkably robust against variations in the metallicity (≈3 {M}⊙ ), the treatment of internal mixing (≈1 {M}⊙ ), and stellar wind mass loss (≈4 {M}⊙ ), making it the most robust predictor for the final stages of the evolution of massive stars. The reason is that the onset of the instability is dictated by the near-final core mass, which in turn sets the resulting BH mass. However, varying the {}12{{C}}{≤ft(α ,γ \right)}16{{O}} reaction rate within its 1σ uncertainties shifts the location of the gap between 40 {M}⊙  and 56 {M}⊙ . We provide updated analytic fits for population synthesis simulations. Our results imply that the detection of merging BHs can provide constraints on nuclear astrophysics. Furthermore, the robustness against metallicity suggests that there is a universal maximum for the location of the lower edge of the gap, which is insensitive to the formation environment and redshift for first-generation BHs. This is promising for the possibility to use the location of the gap as a “standard siren” across the universe.

Keywords: Massive stars, Stellar mass black holes, Stellar mass loss, Supernovae, Astrophysical black holes, Stellar evolution
Modeling Collisional Excitation of [O I] Fine Structure Line Emission from PDRs. I. Homogeneous Clouds. Atomic oxygen (O0) plays a critical role in determining the structure of photon-dominated regions (PDRs), but reliable modeling of its emission has been hampered by the high optical depth of the 63 μm fine structure line and complexities in the excitation of the relevant fine structure levels. We discuss here radiation produced by collisional excitation of the submillimeter fine structure lines of atomic oxygen ([O I]) using recent calculations of rates for collisions with atomic and molecular hydrogen. We employ the Molpop-CEP code to include the effects of optical thickness in slab models that are characterized by uniform oxygen abundance, hydrogen density, and kinetic temperature. The particular spontaneous decay rates and collisional excitation rates connecting the three O0 fine structure levels result in population inversion of the upper, 145 μm transition. The effects of trapping are rigorously included and are reflected in the resulting line profiles that exhibit prominent self-absorption even with uniform physical conditions. We present figures for analyzing the two fine structure lines based on the intensity of the 63 μm line and the 145 μm/63 μm line ratio. For the clouds considered, the results for line intensities and line ratios are modestly different from those obtained with a large-velocity-gradient model, but the ability to calculate line profiles is an additional powerful tool. Comparison of the model results with observed line profiles suggests that cloud models with varying physical conditions are required to optimally utilize [O I] fine structure line emission to trace the energetics of PDR regions and the feedback from massive, young stars.

Keywords: Collision physics, Star forming regions, Radiative transfer, Dense interstellar clouds
Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85. We present a physical characterization of MM J100026.36+021527.9 (a.k.a. “MAMBO-9”), a dusty star-forming galaxy (DSFG) at z = 5.850 ± 0.001. This is the highest-redshift unlensed DSFG (and fourth most distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 μm to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z &gt; 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6→5) and p-H2O (21,1 → 20,2). MAMBO-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M ☉ yr-1 and 220 M ☉ yr-1, total molecular hydrogen gas mass of (1.7 ± 0.4) × 1011 M ☉, dust mass of (1.3 ± 0.3) × 109 M ☉, and stellar mass of ({3.2}-1.5+1.0) × 109 M ☉. The total halo mass, (3.3 ± 0.8) × 1012 M ☉, is predicted to exceed 1015 M ☉ by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τ depl = 40-80 Myr, converting its large molecular gas reservoir (gas fraction of {96}-2+1 % ) into stars. MAMBO-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like MAMBO-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z ≳ 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times (≲1 Gyr).

Keywords: Starburst galaxies, High-redshift galaxies, Infrared galaxies, Blank fields
Fine-scale Explosive Energy Release at Sites of Prospective Magnetic Flux Cancellation in the Core of the Solar Active Region Observed by Hi-C 2.1, IRIS, and SDO. The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56 UT. Three morphologically different types (I: dot-like; II: loop-like; III: surge/jet-like) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter and shorter in span (70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare’s polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA, and IRIS peak nearly simultaneously for many of these events, and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition region origin.

Keywords: Solar active region magnetic fields, Solar magnetic flux emergence, Solar photosphere, Solar active regions, Solar corona, Solar transition region
Nonstationary Fast-driven, Self-organized Criticality in Solar Flares. The original concept of self-organized criticality, applied to solar flare statistics, assumed a slow-driven and stationary flaring rate, which implies timescale separation (between flare durations and interflare waiting times). The concept reproduces power-law distributions for flare peak fluxes and durations, but predicts an exponential waiting time distribution. In contrast to these classical assumptions, we observe (i) multiple energy dissipation episodes during most flares, (ii) violation of the principle of timescale separation, (iii) a fast-driven and nonstationary flaring rate, (iv) a power-law distribution for waiting times Δt, with a slope of α Δt  ≈ 2.0, as predicted from the universal reciprocality between mean flaring rates and mean waiting times, and (v) pulses with rise times and decay times of the dissipated magnetic free energy on timescales of 12 ± 6 minutes, and up to 13 times in long-duration (≲4 hr) flares. These results are inconsistent with coronal long-term energy storage, but require photospheric-chromospheric current injections into the corona.

Keywords: Solar magnetic fields, Solar flares, Solar corona
Living with Neighbors. II. Statistical Analysis of Flybys and Mergers of Dark Matter Halos in Cosmological Simulations. We present a statistical analysis of the flybys of dark matter halos compared to mergers, using cosmological N-body simulations. We mainly focus on gravitationally interacting target halos with mass of 1010.8-1013.0 h -1 M ⊙, and their neighbors are counted only when the mass ratio is 1:3-3:1 and the distance is less than the sum of the virial radii of target and neighbor. The neighbors are divided into the flyby or merger samples if the pair’s total energy is greater or smaller, respectively, than the capture criterion with consideration of dynamical friction. The main results are as follows: (a) the flyby fraction increases by up to a factor of 50 with decreasing halo mass and by up to a factor of 400 with increasing large-scale density, while the merger fraction does not show any significant dependencies on these two parameters; (b) the redshift evolution of the flyby fraction is twofold, increasing with redshift at 0 &lt; z &lt; 1 and remaining constant at z &gt; 1, while the merger fraction increases monotonically with redshift at z = 0 ∼ 4; (c) Multiple interactions with two or more neighbors are on average flyby-dominated, and their fraction has a mass and environment dependence similar to that for the flyby fraction; and (d) Given that flybys substantially outnumber mergers toward z = 0 (by a factor of five) and the multiple interactions are flyby-dominated, the flyby’s contribution to galactic evolution is stronger than ever at the present epoch, especially for less massive halos and in the higher density environment. We propose a scenario that connects the evolution of the flyby and merger fractions to the hierarchical structure formation process.

Keywords: Galaxy dark matter halos, Cosmological evolution, Galaxy environments, Large-scale structure of the universe, Galaxy interactions, N-body simulations, Dark matter, Galaxy encounters
Line Expansion Opacity in Relativistically Expanding Media. Spectral lines of heavy atomic elements in the ejecta of supernovae and neutron star mergers can have important contribution to the opacity of the ejecta matter even when the abundance of the elements is very small. Under favorable conditions, the line expansion opacity arising from spectral lines and the expansion of the medium can be orders of magnitude larger than the opacity of electron scattering. In this paper, we derive the formulae for evaluating the line expansion opacity and its Rosseland mean in an expanding medium in the framework of special relativity, which can be considered as a generalization of previous work in the Newtonian approximation. Then we compare the derived relativistic formulae to the Newtonian ones to explore the relativistic effect on the opacity and test the new formulae with the spectral lines of some heavy atomic elements. We also derive some approximation formulae for the Rosseland mean of the line expansion opacity that are easy to use in numerical works while still maintaining a high-enough accuracy relative to exact solutions. The formulae derived in this paper are expected to have important applications in radiative problems related to relativistic astrophysical phenomena such as neutron star mergers, supernovae, and gamma-ray bursts where relativistic or subrelativistic expansions are involved.

Keywords: Neutron stars, Relativistic mechanics, Atomic physics, Stellar atmospheric opacity, Radiative transfer equation, Radiative transfer, Supernovae
Perpendicular Ion Heating by Cyclotron Resonant Dissipation of Turbulently Generated Kinetic Alfvén Waves in the Solar Wind. Solar wind ions are observed to be heated in the directions perpendicular to the large-scale magnetic field, with preferential heating given to heavy ions. In the solar corona, this heating may be responsible for the generation of the wind itself. It is likely that this heating results from the dissipation of plasma turbulence, but the specific kinetic mechanism that produces these preferential effects is not known. Solar wind turbulence at proton scales is often characterized in terms of highly oblique kinetic Alfvén waves (KAWs), which have been thought to dissipate through the Landau resonance and yield parallel heating. We show that the quasilinear resonant cyclotron interaction between KAWs and solar wind ions can actually produce perpendicular ion heating. We present an illustrative calculation of a steady, critically balanced spectrum of KAWs acting on homogeneous ion distributions with a plasma β = 0.1, representative of turbulent conditions in the fast solar wind near 20 R  s . The KAWs are described here by a two-fluid dispersion relation. We find that thermal protons are strongly heated in the perpendicular direction within a typical quasilinear time of several thousand gyroperiods, which corresponds to only a few minutes at 20 R  s . Alpha particles in the same fluctuation field are heated to similar perpendicular thermal speeds, equivalent to the greater than mass proportional perpendicular temperatures that are commonly observed. We discuss improvements to this simple model that may determine whether this mechanism can be responsible for the observed coronal and solar wind ion heating.

Keywords: Interplanetary turbulence, Space plasmas, Solar coronal heating, Solar wind
Magnetic Helicity Budget of Solar Active Regions Prolific of Eruptive and Confined Flares. We compare the coronal magnetic energy and helicity of two solar active regions (ARs), prolific in major eruptive (AR 11158) and confined (AR 12192) flaring, and analyze the potential of deduced proxies to forecast upcoming flares. Based on nonlinear force-free (NLFF) coronal magnetic field models with a high degree of solenoidality, and applying three different computational methods to investigate the coronal magnetic helicity, we are able to draw conclusions with a high level of confidence. Based on real observations of two solar ARs we checked trends regarding the potential eruptivity of the active-region corona, as suggested earlier in works that were based on numerical simulations, or solar observations. Our results support that the ratio of current-carrying to total helicity, | {H}{{J}}| /| {H}{ \mathcal V }| , shows a strong ability to indicate the eruptive potential of a solar AR. However, | {H}{{J}}| /| {H}{ \mathcal V }| does not seem to be indicative for the magnitude or type of an upcoming flare (confined or eruptive). Interpreted in the context of earlier observational studies, our findings furthermore support that the total relative helicity normalized to the magnetic flux at the NLFF model’s lower boundary, {H}{ \mathcal V }/{φ }2, represents no indicator for the eruptivity.

Keywords: Solar active region magnetic fields, Solar coronal mass ejections, Solar flares, Solar corona
Kinematics: A Clean Diagnostic for Separating Supernova Remnants from H II Regions in Nearby Galaxies. Many more supernova remnants (SNRs) are now known in external galaxies than in the Milky Way. Most of these SNRs have been identified using narrowband imaging, separating SNRs from H II regions on the basis of [S II]:Hα ratios that are elevated compared to H II regions. However, the boundary between SNRs and H II regions is not always distinct, especially at low surface brightness. Here we explore velocity structure as a possible criterion for separating SNRs from H II regions, using a sample of well-studied SNRs in the Large Magellanic Cloud as well as a small number of SNRs in the galaxy M83. We find, perhaps not surprisingly, that even at large diameters, SNRs exhibit velocity broadening sufficient to readily distinguish them from H II regions. We thus suggest that the purity of most extragalactic samples would be greatly improved through spectroscopic observations with a velocity resolution of order 50 km s-1.

Keywords: Supernova remnants, Interstellar medium, Large Magellanic Cloud
Remnants of Subdwarf Helium Donor Stars Ejected from Close Binaries with Thermonuclear Supernovae. Some binary systems composed of a white dwarf (WD) and a hot subdwarf (sdB) helium star will make contact within the helium burning lifetime of the sdB star. The accreted helium on the WD inevitably undergoes a thermonuclear instability, causing a detonation that is expected to transition into the WD core and lead to a thermonuclear supernova (SN) while the donor orbits nearby with high velocity. Motivated by the recent discovery of fast moving objects that occupy unusual locations on the HR diagram, we explore the impact of the thermonuclear SNe on the donors in this specific double detonation scenario. We use MESA to model the binary up to the moment of detonation, then 3D Athena++ to model the hydrodynamic interaction of the SN ejecta with the donor star, calculating the amount of mass that is stripped and the entropy deposited in the deep stellar interior by the strong shock that traverses it. We show that these donor remnants are ejected with velocities primarily set by their orbital speeds: 700-900 km s-1. We model the long-term thermal evolution of remnants by introducing the shock entropy into MESA models. In response to this entropy change, donor remnants expand and brighten for timescales ranging from 106 to 108 yr, giving ample time for these runaway stars to be observed in their inflated state before they leave the galaxy. Even after surface layers are stripped, some donors retain enough mass to resume core helium burning and further delay fading for more than 108 yr.

Keywords: Subdwarf stars, Close binary stars, White dwarf stars, Compact binary stars, High-velocity stars, Runaway stars, Supernovae