Sazuna/UAT_keywords huggingface dataset:
Fast Radio Burst Counterparts and Their Implications for the Central Engine. While the radiation mechanism of fast radio bursts (FRBs) is unknown, coherent curvature radiation and synchrotron maser are promising candidates. We find that both radiation mechanisms work for a neutron star (NS) central engine with B ≳ 1012 G, while for a synchrotron maser, the central engine can also be an accreting black hole (BH) with B ≳ 1012 G and a white dwarf (WD) with B ∼ 108 - 109 G. We study the electromagnetic counterparts associated with such central engines, I.e., nebulae for repeating FRBs and afterglows for nonrepeating FRBs. In general, the energy spectrum and flux density of the counterpart depend strongly on its size and total injected energy. We apply the calculation to the nebula of FRB 121102 and find that the persistent radio counterpart requires the average energy injection rate into the nebula to be between 2.7 × 1039 erg s-1 and 1.5 × 1044 erg s-1, and the minimum injected energy to be 6.0 × 1047 erg in around 7 yr. Consequently, we find that for FRB 121102 and its nebula: (1) WD and accretion BH central engines are disfavored; (2) a rotation-powered NS central engine works when 1.2 × 1012 G ≲ B ≲ 7.8 × 1014 G with initial period P &lt; 180 ms, but the radio emission must be more efficient than that in typical giant pulses of radio pulsars; and (3) a magnetic-powered NS central engine works when its internal magnetic field B ≳ 1016 G. We also find that the radio-emitting electrons in the nebula could produce a significant rotation measure (RM), but cannot account for the entire observed RM of FRB 121102.

Keywords: Magnetars, Non-thermal radiation sources, Radio transient sources
Effects of Scattering, Temperature Gradients, and Settling on the Derived Dust Properties of Observed Protoplanetary Disks. It is known that the millimeter dust thermal emission of protoplanetary disks is affected by scattering, such that for optically thick disks, the emission decreases with respect to the pure absorption case and the spectral indices can reach values below 2. The latter can also be obtained with temperature gradients. Using simple analytical models of radiative transfer in thin slabs, we quantify the effect of scattering, vertical temperature gradients, and dust settling on the emission and spectral indices of geometrically thin face-on accretion disks around young stars. We find that, in vertically isothermal disks with large albedo (ων ≳ 0.6), the emergent intensity can increase at optical depths between 10-2 and 10-1. We show that dust settling has important effects on the spectral indices in the optically thick regime, since the disk emission mainly traces small dust grains in the upper layers of the disk. The λ = 870 μm emission of these small grains can hide large grains at the disk midplane when the dust surface density is larger than ∼3.21 g cm-2. Finally, because of the change of the shape of the spectral energy distribution, optically thick disks at 1.3 mm and grains with sizes between 300 μm &lt; amax &lt; 1 mm have a 7 mm flux ∼60% higher than the extrapolation from higher millimeter frequencies, assumed when scattering is neglected. This effect could provide an explanation for the excess emission at λ = 7 mm reported in several disks.

Keywords: Radio continuum emission, Protoplanetary disks, Radiative transfer, Interstellar scattering, Circumstellar dust
Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V. We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of Vhel = 110.0 ± 0.5 km s-1, Vhel = 15.9-1.7+1.8 km s-1, and Vhel=-36.2-2.2+2.5 km s-1 for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc IV of σ = 4.3-1.0+1.7 km s-1, but we cannot resolve the velocity dispersions of the other two systems. For Gru II, we place an upper limit (90% confidence) on the dispersion of σ &lt; 1.9 km s-1, and for Tuc V, we do not obtain any useful limits. All three satellites have metallicities below [Fe/H]=-2.1, but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru II is on a tightly bound orbit with a pericenter of 25-7+6 kpc and orbital eccentricity of 0.45-0.05+0.08. Tuc V likely has an apocenter beyond 100 kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc IV is similar to that of Gru II, with a pericenter of 25-8+11 kpc and an eccentricity of 0.36-0.06+0.13. However, a backward integration of the position of Tuc IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4 kpc ∼120 Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but the nature of Tuc V remains uncertain.

Keywords: Local Group, Dwarf galaxies, Magellanic Clouds, Dark matter, Milky Way Galaxy
Isotropic Scaling Features Measured Locally in the Solar Wind Turbulence with Stationary Background Field. The scaling anisotropy is crucial to interpret the nonlinear interactions in solar wind turbulence. Previous observations provide diverse results and the structure function analyses are also reported to be an approach to investigate the scaling anisotropy based on a local magnetic field. However, the determination of the sampling angle with respect to the local background magnetic field requires that the observed time series for the average are time stationary. Whether or not this required time stationarity is compatible with the measurements has not been investigated. Here we utilize the second-order structure function method to study the scaling anisotropy with a time-stationary background field. We analyze 88 fast solar wind intervals each with time durations ≥ 2 days measured by WIND spacecraft in the period 2005-2018. We calculate the local magnetic field as the average of the time series B(t^{'} ) whose time stationarity is fulfilled by our criterion φ &lt; 10° (φ is the angle between the two averaged magnetic fields after cutting B(t^{'} ) into two halves). We find for the first time the isotropic scaling feature of the magnetic-trace structure functions with scaling indices -0.63± 0.08 and 0.70 ± 0.04, respectively, with the local magnetic field parallel and perpendicular to the solar wind velocity directions. The scaling for the velocity-trace structure functions is also isotropic and the indices are -0.47 ± 0.10 and 0.51 ± 0.09. We also find that with increasing φ threshold to 90°, the scaling index of the magnetic-trace structure function in the parallel direction decreases to -0.81, while the rms of the instantaneous angle between magnetic field and solar wind velocity increases up to 45° at the timescale 150 s, indicating a mix of perpendicular measurements into parallel ones at large scales.

Keywords: Space plasmas, Solar wind, Magnetic fields, Interplanetary shocks
Spectral Signatures of Quasar Ages at z ≈ 3. Insight into quasar ages may be obtained from the proximity effect, but so far only in a limited number of bright quasars. Based on ∼2600 Sloan Digital Sky Survey quasar spectra at 2.5 ≤ z ≤ 3.5, a search for spectral voids between Lyα forest lines finds proximity zones over a wide range of radial distances. The majority of zone sizes are less than 5 Mpc, with their numbers decreasing exponentially toward larger distances. After a normalization by luminosities, the zone sizes are distributed with an e-folding scale of 0.64 as compared with the anticipated values. A group of quasars are selected for their large proximity zones of ≳10 Mpc. Their composite spectrum displays strong narrow cores and large equivalent widths in Lyα and other major UV emission lines. If the proximity zones along lines of sight are indicative of quasar ages, these features may be the signatures of old quasars. Another group of quasars are selected as they show no proximity zone and exhibit intrinsic absorption lines at zab &gt; zem. They are likely young quasars and exhibit weaker narrow emission-line components. The significant difference of spectral features between the two groups may reflect an evolution pattern over quasars' lifetimes.

Keywords: Quasars
Solar Flare Predictive Features Derived from Polarity Inversion Line Masks in Active Regions Using an Unsupervised Machine Learning Algorithm. The properties of the polarity inversion line (PIL) in solar active regions (ARs) are strongly correlated to flare occurrences. The PIL mask, enclosing the PIL areas, has shown significant potential for improving machine-learning-based flare prediction models. In this study, an unsupervised machine-learning algorithm, Kernel Principle Component Analysis (KPCA), is adopted to directly derive features from the PIL mask and difference PIL mask, and use those features to classify ARs into two categories - non-strong flaring ARs and strong-flaring (M-class and above flares) ARs - for time-in-advance from one hour to 72 hr at a 1 hr cadence. The two best features are selected from the KPCA results to develop random-forest classifiers for predicting flares, and the models are then evaluated and compared to similar models based on the R value and difference R value. The results show that the features derived from the PIL masks by KPCA are effective in predicting flare occurrence, with overall better Fisher ranking scores and similar predictive statistics as the R value characteristics.

Keywords: Space weather, Solar active regions, Solar flares, Classification
Time-resolved and Energy-resolved Polarizations of GRB Prompt Emission. Besides light curves and spectra, polarization provides a different powerful tool of studying the gamma-ray burst (GRB) prompt phase. Compared with the time-integrated and energy-integrated polarization, time-resolved and energy-resolved polarization can deliver more physical information about the emitting region. Here we investigate time-resolved and energy-resolved polarization of GRB prompt emission using the synchrotron models. We find that the equal arrival time surface effect is very important in shaping the polarization degree (PD) curves when the physical conditions of the emitting region change violently with radius. Polarization properties are neither correlated with the spectral lag nor the peak energy evolution patterns. Polarization properties with a mixed magnetic field are very similar to those for a corresponding ordered magnetic field but the former has a smaller PD. The emission at the MeV peak can be highly polarized for a synchrotron model while it is unpolarized as predicted by a dissipative photosphere model. Future energy-resolved polarization observations can distinguish between these two models.

Keywords: Gamma-ray bursts, Magnetic fields
SN 2017cfd: A Normal Type Ia Supernova Discovered Very Young. The Type Ia supernova (SN Ia) 2017cfd in IC 0511 (redshift z=0.01209 ± 0.00016) was discovered by the Lick Observatory Supernova Search 1.6 ± 0.7 day after the fitted first-light time (15.2 days before B-band maximum brightness). Photometric and spectroscopic follow-up observations show that SN 2017cfd is a typical, normal SN Ia with a peak luminosity MB ≈ -19.2± 0.2 mag, Δm15(B) = 1.16 mag, and reached a B-band maximum ∼16.8 days after the first light. We estimate there to be moderately strong host-galaxy extinction (AV = 0.39 ± 0.03 mag) based on MLCS2k2 fitting. The spectrum reveals a Si II λ6355 velocity of ∼11,200 km s-1 at peak brightness. SN 2017cfd was discovered very young, with multiband data taken starting 2 days after the first light, making it a valuable complement to the currently small sample (fewer than a dozen) of SNe Ia with color data at such early times. We find that its intrinsic early-time (B-V)0 color evolution belongs to the "blue" population rather than to the distinct "red" population. Using the photometry, we constrain the companion-star radius to be ≲2.5 R⊙ with the Kasen model, thus ruling out a red-giant companion.

Keywords: Type Ia supernovae
A Small-scale Investigation of Molecular Emission toward the Tip of the Western Lobe of W50/SS 433. We perform a molecular (CO and CN) line observation using the IRAM 30 m telescope toward two small regions near the western edge of supernova remnant (SNR) W50/SS 433. CO observation reveals spatial correspondence of two molecular clumps at the local-standard-of-rest (LSR) velocity around +53 km s01, with multiwavelength local features of the W50/SS 433 system. One of the two clumps appears to be embedded in a void of diffuse radio and X-ray emission. Toward the two clumps, asymmetric broad-line profiles of the 12CO lines are obtained, which provide kinematic evidence of the association between the clumps and the jet-related gas. The 12CO J = 2-1/J = 1-0 line ratios (≳0.9) and the kinetic temperatures (∼30 K) of the clumps are distinctively higher than all those of the clumps at other LSR velocities along the same line of sight, which may be physical signatures of the association. We show that the clump coincident with the void can survive the thermal heating if it is surrounded by hot gas, with an evaporation timescale much larger than the age of SNR W50. We also show that the thermal equilibrium in the high-temperature clumps can be maintained by the heating of the penetrating environmental cosmic rays. CN (J = 3/1-1/2) line emission is detected in the two clumps, and the CN abundances derived are much higher than that in the interstellar molecular clouds (MCs) and that in the SNR-interacting MCs.

Keywords: Supernova remnants, Jets, Molecular clouds, Interstellar medium
A Catalog of M-dwarf Flares with ASAS-SN. We analyzed the light curves of 1376 early-to-late, nearby M dwarfs to search for white-light flares using photometry from the All-Sky Automated Survey for Supernovae. We identified 480 M dwarfs with at least one potential flare employing a simple statistical algorithm that searches for sudden increases in V-band flux. After more detailed evaluation, we identified 62 individual flares on 62 stars. The event amplitudes range from 0.12 lt; Δ V &lt; 2.04 mag. Using classical flare models, we place lower limits on the flare energies and obtain V-band energies spanning 2.0× 1030 ≲ EV ≲ 6.9× 1035 erg. The fraction of flaring stars increases with spectral type, and most flaring stars show moderate to strong Hα emission. Additionally, we find that 14 of the 62 flaring stars are rotational variables, and they have shorter rotation periods and stronger Hα emission than nonflaring rotational variable M dwarfs.

Keywords: Low mass stars, Stellar rotation, Red dwarf flare stars, Stellar activity
ALMA Imaging of the CO (7-6) Line Emission in the Submillimeter Galaxy LESS 073 at z = 4.755. In this paper we present our imaging observations on the CO (7-6) line and its underlying continuum emission of the young submillimeter galaxy LESS 073 at redshift 4.755, using the Atacama Large Millimeter/submillimeter Array. At the achieved resolution of ∼ 1.2" × 0.9" (8 × 6 kpc2), the CO (7-6) emission is largely unresolved (with a deconvolved size of 1.1" ± 0.5" × 0.9" ± 0.8), and the continuum emission is totally unresolved. The CO (7-6) line emission has an integrated flux of 0.86 ± 0.08 Jy km s-1, and a line width of 343 ± 40 km s-1. The continuum emission has a flux density of 0.51 mJy. By fitting the observed far-infrared spectral energy distribution (SED) of LESS 073 with a single-temperature modified blackbody function, we obtained a dust temperature Tdust=57.6± 3.5 K, 60-100 μm flux density ratio f60/f100=0.86± 0.08, and total infrared luminosity LIR=(5.8± 0.9)× 1012 L⊙. The SED-fit-based f60/f100 is consistent with those estimated from various line ratios as advocated by our earlier work, indicating that the proposed line-ratio-based method can be used to practically derive f60/f100 for high-z sources. The total molecular gas mass of LESS 073 is (3.3 ± 1.7)× 1010 M⊙, and the inferred gas depletion time is about 43 Myr.

Keywords: Starburst galaxies, High-redshift galaxies, Galaxy evolution, Interstellar medium
GASP XXIV. The History of Abruptly Quenched Galaxies in Clusters. The study of cluster post-starburst galaxies gives useful insights on the physical processes quenching the star formation in the most massive environments. Exploiting the Multi Unit Spectroscopic Explorer data of the GAs Stripping Phenomena in galaxies project, we characterize the quenching history of eight local cluster galaxies that were selected for not showing emission lines in their fiber spectra. We inspect the integrated colors, the Hβ rest-frame equivalent widths (EW), star-formation histories (SFHs), and luminosity-weighted age (LWA) maps finding no signs of current star formation throughout the disks of these early-spiral/S0 galaxies. All of them have been passive for at least 20 Myr, but their SF declined on different timescales. In most of them, the outskirts reached undetectable SFRs before the inner regions ("outside-in quenching"). Our sample includes three post-star-forming galaxies, two passive galaxies, and three galaxies with intermediate properties. The first population shows blue colors, deep Hβ in absorption (EW ≫ 2.8 Å), young ages (8.8 &lt; log(LWA (yr)) &lt; 9.2). Two of these galaxies show signs of a central SF enhancement before quenching. Passive galaxies have instead red colors, EW(Hβ) &lt; 2.8 Å, ages in the range 9.2 &lt; log(LWA (yr)) &lt; 10. Finally, the other galaxies are most likely in transition between a post-star-forming and passive phase, as they quenched in an intermediate epoch and have not lost all of the star-forming features yet. The outside-in quenching, the morphology, and kinematics of the stellar component, along with the position of these galaxies within massive clusters (σcl = 550-950 km s-1) point to a scenario in which ram pressure stripping has removed the gas, leading to quenching. Only the three most massive galaxies might alternatively have entered the clusters already quenched. These galaxies are therefore at the final stage of the rapid evolution galaxies undergo when they enter the cluster environment.

Keywords: Galaxy clusters, Galaxy formation, E+A galaxies, Star formation, Galaxy evolution, Galaxies
Oversized Gas Clumps in an Extremely Metal-poor Molecular Cloud Revealed by ALMA's Parsec-scale Maps. Metals are thought to have profound effects on the internal structures of the molecular clouds in which stars are born. The absence of metals is expected to prevent gas from efficient cooling and fragmentation in theory. However, this effect has not yet been observed in low-metallicity environments, such as in the early universe and local dwarf galaxies, because of the lack of high-spatial-resolution maps of gas. We carried out Atacama Large Millimeter/submillimeter Array observations of the carbon monoxide (CO) J = 2-1 emission line at 1.4 parsec resolutions of a molecular cloud in DDO 70 at 7% solar metallicity, the most metal-poor galaxy currently known with a CO detection. In total, five clumps have been identified and they are found to more or less follow Larson's law. Since the CO emission exists in regions with visual extinction AV around 1.0, we converted this AV to the gas-mass surface density using a gas-to-dust ratio of 4594 ± 2848 for DDO 70. We found that the CO clumps in DDO 70 exhibit significantly larger (on average four times) sizes than those at the same gas-mass surface densities in the massive star formation regions of the Milky Way. The existence of such large clumps appears to be consistent with theoretical expectations that gas fragmentation in low-metallicity clouds is suppressed. While our observation is only for one cloud in the galaxy, if it is representative, the above result implies suppressed gas fragmentation during the cloud collapse and star formation in the early universe.

Keywords: Giant molecular clouds, Interstellar medium, Dwarf irregular galaxies
Dynamical Equilibrium in the Molecular ISM in 28 Nearby Star-forming Galaxies. We compare the observed turbulent pressure in molecular gas, Pturb, to the required pressure for the interstellar gas to stay in equilibrium in the gravitational potential of a galaxy, PDE. To do this, we combine arcsecond resolution CO data from PHANGS-ALMA with multiwavelength data that trace the atomic gas, stellar structure, and star formation rate (SFR) for 28 nearby star-forming galaxies. We find that Pturb correlates with - but almost always exceeds - the estimated PDE on kiloparsec scales. This indicates that the molecular gas is overpressurized relative to the large-scale environment. We show that this overpressurization can be explained by the clumpy nature of molecular gas; a revised estimate of PDE on cloud scales, which accounts for molecular gas self-gravity, external gravity, and ambient pressure, agrees well with the observed Pturb in galaxy disks. We also find that molecular gas with cloud-scale Pturb ≈ PDE ≳ 105 kB K cm-3 in our sample is more likely to be self-gravitating, whereas gas at lower pressure it appears more influenced by ambient pressure and/or external gravity. Furthermore, we show that the ratio between Pturb and the observed SFR surface density, ΣSFR, is compatible with stellar feedback-driven momentum injection in most cases, while a subset of the regions may show evidence of turbulence driven by additional sources. The correlation between ΣSFR and kpc-scale PDE in galaxy disks is consistent with the expectation from self-regulated star formation models. Finally, we confirm the empirical correlation between molecular-to-atomic gas ratio and kpc-scale PDE reported in previous works.

Keywords: Interstellar molecules, Star formation, Interstellar dynamics
Dust Destruction by Drift-induced Sputtering in Active Galactic Nuclei. Recent mid-infrared high spatial resolution observations have revealed that active galactic nuclei (AGNs) may host a polar dust region with the size of several pc, and such dust may be carried by radiation from the central engine. The polar dust emission often exhibits very weak or absence of the silicate 10 μm emission feature. A possible explanation is that the polar dust is dominated by micron-sized large grains because these grains do not show the silicate feature, while it remains unclear how large grains are preferentially supplied to the polar region. Here, we propose a new scenario describing the prevalence of large grains at the polar region. We show that grains are accelerated to the hypersonic drift velocity by the radiation pressure from AGN, and the hypersonic drift results in dust destruction via kinetic sputtering. Sputtering destroys small grains faster than the large ones, and thus larger grains will be preferentially blown over longer distance. Although the hypersonic drift, or kinetic sputtering, tends to be suppressed for very small grains due to the Coulomb drag, they might also be disrupted by Coulomb explosion. Removal of small grains and/or survival of large grains may explain the lack of a silicate 10 μm emission feature in polar dust emission.

Keywords: Astrophysical dust processes, Dust continuum emission, Active galactic nuclei