Sazuna/UAT_keywords huggingface dataset:
The HSC-SSP Transient Survey: Implications from Early Photometry and Rise Time of Normal Type Ia Supernovae. With a booming number of Type Ia supernovae (SNe Ia) discovered within a few days of their explosions, a fraction of SNe Ia that show luminosity excess in the early phase (early-excess SNe Ia) have been confirmed. In this article, we report early-phase observations of seven photometrically normal SNe Ia (six early detections and one deep non detection limit) at the COSMOS field through a half-year transient survey as a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP). In particular, a blue light-curve excess was discovered for HSC17bmhk, a normal SN Ia with rise time longer than 18.8 days, during the first four days after the discovery. The blue early excess in optical wavelength can be explained not only by interactions with a nondegenerate companion or surrounding dense circumstellar matter but also radiation powered by radioactive decays of 56Ni at the surface of the SN ejecta. Given the growing evidence of the early-excess discoveries in normal SNe Ia that have longer rise times than the average, and a similarity in the nature of the blue excess to a luminous SN Ia subclass, we infer that early excess discovered in HSC17bmhk and other normal SNe Ia are most likely attributed to radioactive 56Ni decay at the surface of the SN ejecta. In order to successfully identify normal SNe Ia with early excess similar to that of HSC17bmhk, early UV photometries or high-cadence blue-band surveys are necessary.

Keywords: Type Ia supernovae, Supernovae
Stellar Density Profiles of Dwarf Spheroidal Galaxies. We apply a flexible parametric model, a combination of generalized Plummer profiles, to infer the shapes of the stellar density profiles of the Milky Way's satellite dwarf spheroidal galaxies (dSphs). We apply this model to 40 dSphs using star counts from the Sloan Digital Sky Survey, PanStarrs-1 Survey, Dark Energy Survey, and Dark Energy Camera Legacy Survey. Using mock data, we examine systematic errors associated with modeling assumptions and identify conditions under which our model can identify "non-standard" stellar density profiles that have central cusps and/or steepened outer slopes. Applying our model to real dwarf spheroidals, we do not find evidence for centrally cusped density profiles among the fifteen Milky Way satellites for which our tests with mock data indicate there would be sufficient detectability. We do detect steepened (with respect to a standard Plummer model) outer profiles in several dSphs—Fornax, Leo I, Leo II, and Reticulum II—which may point to distinct evolutionary pathways for these objects. However, the outer slope of the stellar density profile does not yet obviously correlate with other observed galaxy properties.

Keywords: Dwarf spheroidal galaxies
SN 2010kd: Photometric and Spectroscopic Analysis of a Slow-decaying Superluminous Supernova. This paper presents data and analysis of SN 2010kd, a low-redshift (z = 0.101) H-deficient superluminous supernova (SLSN), based on ultraviolet/optical photometry and optical spectroscopy spanning between -28 and +194 days relative to B-band maximum light. The B-band light-curve comparison of SN 2010kd with a subset of well-studied SLSNe I at comparable redshifts indicates that it is a slow-decaying PTF12dam-like SLSN. Analytical light-curve modeling using the Minim code suggests that the bolometric light curve of SN 2010kd favors circumstellar matter interaction for the powering mechanism. SYNAPPS modeling of the early-phase spectra does not identify broad H or He lines, whereas the photospheric-phase spectra are dominated by O I, O II, C II, C IV, and Si II, in particular the presence of both low- and high-velocity components of O II and Si II lines. The nebular-phase spectra of SN 2010kd are dominated by O I and Ca II emission lines similar to those seen in other SLSNe I. The line velocities in SN 2010kd exhibit flatter evolution curves similar to SN 2015bn but with comparatively higher values. SN 2010kd shows a higher single-zone local thermodynamic equilibrium temperature in comparison to PTF12dam and SN 2015bn, and it has an upper O I ejected mass limit of ∼10 M⊙. The host of SN 2010kd is a dwarf galaxy with a high star formation rate (∼0.18 ± 0.04 M⊙ yr-1) and extreme emission lines.

Keywords: Photometry, Supernovae, Core-collapse supernovae, Spectroscopy
A Second Look at 12 Candidate Dual AGNs Using BAYMAX. We present an analysis of 12 optically selected dual active galactic nucleus (AGN) candidates at z &lt; 0.34. Each candidate was originally identified via double-peaked [O III] λ5007 emission lines and received follow-up Chandra and Hubble Space Telescope (HST) observations. Because the X-ray data are low-count (&lt;100 counts) with small separations (&lt;1″), a robust analysis is necessary for classifying each source. Pairing long-slit [O III] observations with existing Chandra observations, we re-analyze the X-ray observations with Bayesian AnalYsis of AGNs in X-rays to determine whether the X-ray emission from each system is more likely a single or dual point source. We find that 4 of the 12 sources are likely dual X-ray point-source systems. We examine each point source's spectra via a Monte Carlo method that probabilistically identifies the likely origin of each photon. When doing so, we find that (I) the secondary X-ray point sources in two of the systems have LX &lt; 1040 erg s-1, such that we cannot rule out a non-AGN origin, (II) one source has a secondary with LX &gt; 1040 erg s-1 but a spectrum that is too soft to definitively preclude being X-ray emitting diffuse gas that was photoionized by the primary AGN, and (III) one system (SDSS J1126+2944) is a dual AGN. Additionally, using complementary HST observations, we analyze a subsample of systems that are visually identified as merging. Our results suggest that dual AGNs may preferentially reside in mergers with small separations, consistent with both simulations and observations.

Keywords: AGN host galaxies, X-ray astronomy, Active galactic nuclei, Galaxy mergers
A Comprehensive Study of Hα Emitters at z ∼ 0.62 in the DAWN Survey: The Need for Deep and Wide Regions. We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an Hα-selected sample at z ∼ 0.62 from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new Hα sample in the extended COSMOS region (compared to Coughlin et al.) with the inclusion of flanking fields, resulting in a total area coverage of ∼1.5 deg2. A total of 241 Hα emitters were selected based on robust selection criteria using spectrophotometric redshifts and broadband color-color classification. Given that dust extinction is a dominant uncertainty in the estimation of LF and SFRD, we explore the effect of different dust-correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, AHα = 1 mag, a luminosity-dependent correction, and a stellar-mass-dependent correction. The resulting Hα LFs are well fitted using Schechter functions with best-fit parameters: L* = 1042.24 erg s-1, φ* = 10-2.85 Mpc-3, α = -1.62 for constant dust correction, L*=1042.31 erg s-1, φ* = 10-2.8 Mpc-3, α = -1.39 for luminosity-dependent dust correction, and L* = 1042.36 erg s-1, φ* = 10-2.91 Mpc-3, α = -1.48, for stellar-mass-dependent dust correction. The deep and wide nature of the DAWN survey effectively samples Hα emitters over a wide range of luminosities, thereby providing better constraints on both the faint and bright ends of the LF. Also, the SFRD estimates ρSFR = 10-1.39 M☉ yr-1 Mpc-3 (constant dust correction), ρSFR = 10-1.47 M☉ yr-1 Mpc-3 (luminosity-dependent dust correction), and ρSFR = 10-1.46 M☉ yr-1 Mpc-3 (stellar-mass-dependent dust correction) are in good agreement with the evolution of SFRD across redshifts (0 &lt; z &lt; 2) seen from previous Hα surveys.

Keywords: Luminosity function, Star forming regions, Star formation, Emission line galaxies
Temperatures and Metallicities of M Dwarfs in the APOGEE Survey. M dwarfs have enormous potential for our understanding of structure and formation on both Galactic and exoplanetary scales through their properties and compositions. However, current atmosphere models have limited ability to reproduce spectral features in stars at the coolest temperatures (Teff &lt; 4200 K) and to fully exploit the information content of current and upcoming large-scale spectroscopic surveys. Here we present a catalog of spectroscopic temperatures, metallicities, and spectral types for 5875 M dwarfs in the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and Gaia-DR2 surveys using The Cannon: a flexible, data-driven spectral-modeling and parameter-inference framework demonstrated to estimate stellar-parameter labels (Teff, log g, [Fe/H], and detailed abundances) to high precision. Using a training sample of 87 M dwarfs with optically derived labels spanning 2860 K &lt; Teff &lt; 4130 K calibrated with bolometric temperatures, and -0.5&lt; [Fe/H]&lt; 0.5 dex calibrated with FGK binary metallicities, we train a two-parameter model with predictive accuracy (in cross-validation) to 77 K and 0.09 dex respectively. We also train a one-dimensional spectral classification model using 51 M dwarfs with Sloan Digital Sky Survey optical spectral types ranging from M0 to M6, to predictive accuracy of 0.7 types. We find Cannon temperatures to be in agreement to within 60 K compared to a subsample of 1702 sources with color-derived temperatures, and Cannon metallicities to be in agreement to within 0.08 dex metallicity compared to a subsample of 15 FGK+M or M+M binaries. Finally, our comparison between Cannon and APOGEE pipeline (ASPCAP DR14) labels finds that ASPCAP is systematically biased toward reporting higher temperatures and lower metallicities for M dwarfs.

Keywords: M dwarf stars, High resolution spectroscopy, Surveys, Stellar abundances, Astronomy data analysis
A New Method to Constrain the Origins of Dark-matter-free Galaxies and Their Unusual Globular Clusters. We present a novel method to constrain the past collisional evolution of observed globular cluster (GC) systems, in particular their mass functions. We apply our method to a pair of galaxies hypothesized to have recently undergone an episode of violent relaxation due to a strong galaxy-galaxy interaction, namely, NGC 1052-DF2 and NGC 1052-DF4. We begin by exploring the observational evidence for a collisional origin for these two recently discovered ultradiffuse galaxies observed in the NGC 1052 group, posited in the literature to be dark matter free. We compute the timescales for infall to the central nucleus due to dynamical friction for the GCs in these galaxies, using the shortest of these times to constrain how long ago a galaxy-galaxy interaction could have occurred. We go on to quantify the initial GC numbers and densities needed for significant collisional evolution to occur within the allotted times and show that, if the hypothesis of a previous galaxy-galaxy interaction is correct, a paucity of low-mass GCs should be revealed by deeper observational surveys. If any are found, they should be more spatially extended than the currently observed GC population. Finally, we apply our method to these galaxies, in order to illustrate its efficacy in constraining their dynamical evolution. Our results motivate more complete observations of the GC luminosity functions in these galaxies, in addition to future studies aimed at combining the method presented here with a suite of numerical simulations in order to further constrain the origins of the curious GC populations in these (and other) galaxies.

Keywords: Galaxy clusters, Interacting galaxies, Stellar dynamics, Globular star clusters
Hot Gas in Galaxy Halos Traced by Coronal Broad Lyα Absorbers. We explore the possibility to systematically study the extended, hot gaseous halos of low-redshift galaxies with coronal broad Lyα absorbers (CBLAs). These are weak, thermally broadenend H I absorption lines arising from the tiny fraction of neutral hydrogen that resides in the collisionally ionized, million-degree halo gas in these galaxies. Using a semi-analytic approach, we model the spatial density and temperature distribution of hot coronal gas to predict strength, spectral shape, and cross section of CBLAs as a function of galaxy-halo mass and line-of-sight impact parameter. For virial halo masses in the range log (M/M⊙)=10.6-12.6, the characteristic logarithmic CBLA H I column densities and Doppler parameters are log N(H I) = 12.4-13.4 and b(H I) = 70-200 km s-1, indicating that CBLAs represent weak, shallow spectral features that are difficult to detect. Yet, the expected number density of CBLAs per unit redshift in the above given mass range is dN/dz (CBLA) ≈ 3, implying that CBLAs have a substantial absorption cross section. We compare the model predictions with a combined set of UV absorption-line spectra from the Hubble Space Telescope (HST)/Cosmic Origins Spectrograph and HST/Space Telescope Imaging Spectrograph that trace the halos of four low-redshift galaxies. We demonstrate that CBLAs might already have been detected in these spectra, but the complex multi-component structure and the limited signal-to-noise ratio complicate the interpretation of these CBLA candidate systems. Our study suggests that CBLAs represent a very interesting absorber class that potentially will allow us to further explore the hot coronae of galaxies with UV spectral data.

Keywords: Astronomical models, Galaxy evolution, Quasar absorption line spectroscopy, Circumgalactic medium
Stellar-mass Measurements in A133 with Magellan/IMACS. We present the analysis of deep optical imaging of the galaxy cluster A133 with the IMACS instrument on Magellan. Our multi-band photometry enables stellar-mass measurements in the cluster member galaxies down to a mass limit of M{\star }3× 108 M⊙ (≈0.1 of the Large Magellanic Cloud stellar mass). We observe a clear difference in the spatial distribution of large and dwarf galaxies within the cluster. Modeling these galaxy populations separately, we can confidently track the distribution of stellar mass locked in the galaxies to the cluster's virial radius. The extended envelope of the cluster's brightest galaxy can be tracked to ∼200 kpc. The central galaxy contributes ∼1/3 of the total cluster stellar mass within the radius r500c.

Keywords: Galaxy clusters, Galaxies, Stellar mass functions, Photometry
A Toy Model for the Electromagnetic Output of Neutron-star Merger Prompt Collapse to a Black Hole: Magnetized Neutron-star Collisions. We present a systematic study of magnetized neutron star head-on collisions. We investigate the resulting magnetic field geometries as the two neutron stars merge. Furthermore, we analyze the luminosity produced in these collisions and monitor the evolution of the magnetic fields from the time of merger until the subsequent production of a black hole. At the time of black hole formation, the luminosity peaks and rings down following the decay of the electromagnetic fields. A comparison is presented for three different cases: one where the initial magnetic field in both neutron stars is aligned, one where they are anti-aligned, and one where they initially have unequal magnetic field strength. We identify regions and set limits so that pair creation and magnetic reconnection would occur in this scenario and further discuss limits and differences in the radiated energy. This study should be regarded as a toy model of the case where the remnant of a binary neutron star merger undergoes a prompt collapse to a black hole with a negligible surrounding disk. We note that the generated electromagnetic pulses resemble the fast radio burst phenomenology. We consider implications of the high-mass mergers leading to a fast prompt collapse to a black hole and the expected flux to be observed at a distance similar to the binary neutron star gravitational wave detection GW190425.

Keywords: Neutron stars, Gravitational waves, Compact objects, Magnetohydrodynamical simulations
Making a Supermassive Star by Stellar Bombardment. Approximately 200 supermassive black holes (SMBHs) have been discovered within the first ∼gigayear after the Big Bang. One pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs). A possible obstacle to this scenario is that the collapsing gas fragments and forms a cluster of main-sequence stars. Here, we raise the possibility that stellar collisions may be sufficiently frequent and energetic to inhibit the contraction of the massive protostar, avoiding strong UV radiation driven outflows, and allowing it to continue growing into an SMS. We investigate this scenario with semianalytic models incorporating star formation; gas accretion; dynamical friction from stars and gas; stellar collisions; and gas ejection. We find that when the collapsing gas fragments at a density of ≲3 × 1010 cm-3, the central protostar contracts due to infrequent stellar mergers, and in turn photoevaporates the remaining collapsing gas, resulting in the formation of a ≲104 M⊙ object. On the other hand, when the collapsing gas fragments at higher densities (expected for a metal-poor cloud with Z ≲ 10-5 Z⊙ with suppressed H2 abundance) the central protostar avoids contraction and keeps growing via frequent stellar mergers, reaching masses as high as ∼105-106 M⊙. We conclude that frequent stellar mergers represent a possible pathway to form massive BHs in the early universe.

Keywords: Supermassive black holes, Early universe, Quasars, Primordial galaxies, Pre-main sequence, Population II stars
Properties of Trans-fast Magnetosonic Jets in Black Hole Magnetospheres. Traveling across several orders of magnitude in distance, relativistic jets from strong gravity regions to asymptotic flat spacetime regions are believed to consist of several general relativistic magnetohydrodynamic (GRMHD) processes. We present a semianalytical approach for modeling the global structures of a trans-fast magnetosonic relativistic jet, which should be ejected from a plasma source near a black hole in a funnel region enclosed by dense accreting flow and a disk corona around the black hole. Our model consistently includes the inflow and outflow part of the GRMHD solution along the magnetic field lines penetrating the black hole horizon. After the rotational energy of the black hole is extracted electromagnetically by the negative energy GRMHD inflow, the huge electromagnetic energy flux propagates from the inflow to the outflow region across the plasma source, and in the outflow region, the electromagnetic energy converts to the fluid kinetic energy. Eventually, the accelerated outflow must exceed the fast magnetosonic wave speed. We apply the semianalytical trans-fast magnetosonic flow model to the black hole magnetosphere for both parabolic and split-monopole magnetic field configurations and discuss the general flow properties, that is, jet acceleration, jet magnetization, and the locations of some characteristic surfaces of the black hole magnetosphere. We have confirmed that, at large distances, the GRMHD jet solutions are in good agreement with the previously known trans-fast special relativistic magnetohydrodynamic jet properties, as expected. The flexibility of the model provides a prompt and heuristic way to approximate the global GRMHD trans-fast magnetosonic jet properties.

Keywords: Accretion, Black hole physics, Magnetohydrodynamics, Jets, Kerr black holes, Relativistic jets, Galaxy jets, Rotating black holes, Magnetic fields, Astrophysical black holes
Spot Model for Identifications of Periods in Asynchronous Polars. We improved the discless accretion models in Wynn &amp; King considering the effects of the changing aspect due to the white dwarf (WD) spin and the variable feeding intensity caused by the asynchronism, and set up a more general spot model that is not sensitive to the different forms of these effects and can be applied for the period analysis of the optical and X-ray light curve. The spot model can produce the power spectra compatible with the observations, and its simulations limit the ratio Pspin/Porb &lt; 2 between the powers at the WD spin and the binary orbital frequencies, which is a strong criterion for identification of periods. Then we recognize the periods for CD Ind, BY Cam, and 1RXS J083842.1-282723. The spot model reveals a complex accretion geometry in the asynchronous polars (APs), which may indicate that the complex magnetic field causes their asynchronism. We think 1RXS J083842.1-282723 is a prepolar because of its highest asynchronism and stable light curve. Giving the unstable accretion process in APs, the period analysis of the long-term light curve will make the orbital signal prominent.

Keywords: X-ray photometry, X-ray binary stars, AM Herculis stars, CCD photometry
The Proper Motion of Sagittarius A*. III. The Case for a Supermassive Black Hole. We report measurements with the Very Long Baseline Array of the proper motion of Sgr A* relative to two extragalactic radio sources spanning 18 yr. The apparent motion of Sgr A* is -6.411 ± 0.008 mas yr-1 along the Galactic plane and -0.219 ± 0.007 mas yr-1 toward the North Galactic Pole. This apparent motion can almost entirely be attributed to the effects of the Sun's orbit about the Galactic center. Removing these effects yields residuals of -0.58 ± 2.23 km s-1 in the direction of Galactic rotation and -0.85 ± 0.75 km s-1 toward the North Galactic Pole. A maximum-likelihood analysis of the motion, both in the Galactic plane and perpendicular to it, expected for a massive object within the Galactic center stellar cluster indicates that the radiative source, Sgr A*, contains more than about 25% of the gravitational mass of 4 × 106 M⊙ deduced from stellar orbits. The intrinsic size of Sgr A* is comparable to its Schwarzschild radius, and the implied mass density of ≳ 4× 1023 M⊙ pc-3 is very close to that expected for a black hole, providing overwhelming evidence that it is indeed a supermassive black hole. Finally, "intermediate mass" black holes more massive than ≈3 × 104 M⊙ between approximately 0.003 and 0.1 pc from Sgr A* are excluded.

Keywords: Supermassive black holes, Galactic center, Milky Way dynamics, Milky Way Galaxy physics, Astrometry