Table of contents

We investigate the onset of a GOES M3.7 flare on 2017 September 9 with rapid-cadence (9.4 s) UV stare spectra obtained with IRIS in five 1'' slit segments. Our analysis is based primarily on integrated intensities and Doppler velocities of C iiλ1334.5 (T ≈ 2.5 × 10⁴ K), Si ivλ1402.7 (7.9 × 10⁴ K), and Fe xxiλ1354.1 (1.1 × 10⁷ K). The four segments within the ribbon show systematically earlier starting times for the low-T lines (C ii and Si iv) than Fe xxi; further, the velocities derived for Fe xxi are generally directed upward along the line of sight. This is consistent with the standard flare model, in which beams of nonthermal particles ionize and heat the chromosphere and drive chromospheric evaporation: as the temperature and ionization stages of the chromospheric plasma increase, intensities of emission lines also increase, first from lines in lower stages of ionization, and later from lines in higher stages of ionization. Where quasi-periodic fluctuations were observed in the ribbon in both low-T and Fe xxi emission, peaks in the low-T intensity preceded those in the Fe xxi intensity, and peaks in the Fe xxi upward velocity typically also preceded those in the Fe xxi intensity. Thus, the behavior of each individual fluctuation was similar to that of a standard flare, suggesting that each individual fluctuation was due to a separate injection of nonthermal particles into the chromosphere. Based on RHESSI hard X-ray observations, we estimate sufficient beam energy flux (≥1.5 × 10¹⁰ erg cm⁻² s⁻¹) to drive explosive chromospheric evaporation.

We present the X-ray spectral and timing analysis of the transient black hole X-ray binary 4U 1630–47, observed with the AstroSat, Chandra, and MAXI space missions during its soft X-ray outburst in 2016. The outburst, from the rising phase until the peak, is detected neither in hard X-rays (15–50 keV) by the Swift/BAT nor in radio. Such nondetection, along with the source behavior in the hardness–intensity and color–color diagrams obtained using MAXI data, confirms that both Chandra and AstroSat observations were performed during the HS spectral state. The High Energy Grating (HEG) spectrum from the Chandra High-Energy Transmission Grating Spectrometer shows two strong, moderately blueshifted absorption lines at ${6.705}_{-0.002}^{+0.002}$ keV and ${6.974}_{-0.003}^{+0.004}$ keV, which are produced by Fe xxv and Fe xxvi in a low-velocity ionized disk wind. The corresponding outflow velocity is determined to be 366 ± 56 km s⁻¹. Separate spectral fits of Chandra/HEG, AstroSat/SXT+LAXPC, and Chandra/HEG+AstroSat/SXT+LAXPC data show that the broadband continuum can be well described with a relativistic disk blackbody model, with a disk flux fraction of ∼0.97. Based on the best-fit continuum spectral modeling of Chandra, AstroSat, and Chandra+AstroSat joint spectra and using the Markov chain Monte Carlo simulations, we constrain the spectral hardening factor at ${1.56}_{-0.06}^{+0.14}$ and the dimensionless black hole spin parameter at 0.92 ± 0.04 within the 99.7% confidence interval. Our conclusion of a rapidly spinning black hole in 4U 1630–47 using the continuum spectrum method is in agreement with a previous finding applying the reflection spectral fitting method.

The nonadiabatic nuclear dynamics for the 17 low-lying molecular states of the ${\mathrm{CaH}}^{+}$ collisional system is studied by the probabilistic version of the hopping probability current method based on the accurate ab initio adiabatic potentials. Inelastic Ca⁺ + H, Ca + H⁺, and Ca²⁺ + H⁻ collisions are treated, and partial cross sections and rate coefficients for all transitions between the considered scattering channels are calculated for excitation, de-excitation, charge exchange, ion-pair formation, and neutralization processes. The cross sections and the rate coefficients for the 272 partial inelastic processes are computed. It is found that the reaction mechanism for the partial processes with high-valued rates is due to the long-range ionic–covalent interaction, while for some processes with moderate-valued rates it is due to short-range nonadiabatic regions. It is shown that the largest rate coefficients correspond to the neutralization and also charge exchange processes from the optimal window. The largest rate coefficient exceeds the value ${10}^{-7}\,{\mathrm{cm}}^{3}\,{{\rm{s}}}^{-1}$. It is also found that some two-electron-transition charge exchange processes have rate coefficients as large as one-electron-transition processes. The processes with large and moderate values of rate coefficients are likely to be important for stellar spectra modeling.

We present spatially resolved mass outflow rate measurements (${\dot{M}}_{\mathrm{out}}$) for the narrow line region of Markarian 34, the nearest Compton-thick type 2 quasar (QSO2). Spectra obtained with the Hubble Space Telescope and at Apache Point Observatory reveal complex kinematics, with distinct signatures of outflow and rotation within 2 kpc of the nucleus. Using multi-component photoionization models, we find that the outflow contains a total ionized gas mass of M ≈ 1.6 × 10⁶M_⊙. Combining this with the kinematics yields a peak outflow rate of ${\dot{M}}_{\mathrm{out}}\approx 2.0\pm 0.4$M_⊙ yr⁻¹ at a distance of 470 pc from the nucleus, with a spatially integrated kinetic energy of E ≈ 1.4 × 10⁵⁵ erg. These outflows are more energetic than those observed in Mrk 573 and NGC 4151, supporting a correlation between luminosity and outflow strength even though they have similar peak outflow rates. The mix of rotational and outflowing components suggests that spatially resolved observations are required to determine accurate outflow parameters in systems with complex kinematics.

We present a systematic study of sunspot physical parameters using full-disk magnetograms from the Michelson Doppler Imager/Solar and Heliospheric Observatory and the Helioseismic and Magnetic Imager/Solar Dynamic Observatory. Our aim is to use uniform data sets and analysis procedures to characterize the sunspots, paying particular attention to the differences and similarities between "Hale" and "anti-Hale" spots. Included are measurements of the magnetic tilt angles, areas, fluxes, and polarity pole separations for 4385 sunspot groups in Cycles 23 and 24 each measured, on average, at ∼66 epochs centered on meridian crossing. The sunspots are classified as either "Hale" or "anti-Hale," depending on whether their polarities align or anti-align with Hale's hemispheric polarity rule. We find that (1) the "anti-Hale" sunspots constitute a fraction (8.1 ± 0.4)% of all sunspots, and this fraction is the same in both hemispheres and cycles; (2) "Hale" sunspots obey Joy's law in both hemispheres and cycles but "anti-Hale" sunspots do not—three equivalent forms of Joy's law are derived: $\sin \gamma =(0.38\pm 0.05)\,\sin \,\phi ,$γ = (0.39 ± 0.06) ϕ, and $\gamma =(23.80\pm 3.51)\,\sin \,\phi$, where γ is the tilt angle and ϕ is the heliospheric latitude; (3) the average Hale sunspot tilt angle is $\overline{\gamma }=5\buildrel{\circ}\over{.} 49\pm 0.09;$ and (4) the tilt angles, magnetic fluxes, and pole separations of sunspots are interrelated, with larger fluxes correlated with larger pole separations and smaller tilt angles. We present empirical relations between these quantities. Cycle 24 is a much weaker cycle than Cycle 23 in sunspot numbers, cumulative magnetic flux, and average sunspot magnetic flux. The "anti-Hale" sunspots are also much weaker than "Hale" sunspots in those parameters, but they share similar magnetic flux distributions and average latitudes. We characterize the two populations, and aim to shed light on the origin of "anti-Hale" sunspots.

Using 9.5 yr of Fermi Large Area Telescope data, we report the evidence on the orbital modulated gamma-ray emissions from the redback candidate 3FGL J2039.6–5618. We produced the folded light curve with the orbital period of ∼5.47 hr at a ∼4σ level. We also computed the gamma-ray spectra in two orbital phases corresponding to the inferior conjunction and the superior conjunction. We found that the <3 GeV excess in the spectrum of inferior conjunction can be modeled by the inverse Compton scattering between a relativistic pulsar wind and background soft photons of the companion star. The orbital modulation can also be explained by the evolving collision angle between the particles and photons in the same model. Through period searches by the Rayleigh test and the flux variability, we speculate that the orbital modulation is not detected after MJD ∼57,000. We propose a possible explanation in which the intrabinary shock is located closer to the pulsar so that the pulsar wind carries a smaller Lorentz factor. We estimated that the resultant inverse Compton component will be too soft and too weak to be observed.

Interstellar dust spans a wide range in size distribution, ranging from ultrasmall grains of a few Ångströms to micrometer-size grains. While the presence of nanometer-size dust grains in the Galactic interstellar medium was speculated six decades ago and was previously suggested based on early infrared observations, systematic and direct analysis of their properties over a wide range of environments has been lacking. Here we report the detection of nanometer-size dust grains that appear to be universally present in a wide variety of astronomical environments, from Galactic high-latitude clouds to nearby star-forming galaxies and galaxies with low levels of nuclear activity. The prevalence of such a grain population is revealed conclusively as prominent mid-infrared continuum emission at λ ≲ 10 μm seen in the Spitzer/Infrared Spectrograph data, characterized by temperatures of ∼300–400 K that are significantly higher than the equilibrium temperatures of common, submicron-size grains in typical galactic environments. We propose that the optimal carriers of this pervasive, featureless hot dust component are very small carbonaceous (e.g., graphite) grains of nanometer size that are transiently heated by single-photon absorption. This grain population accounts for ∼1.4% of the total infrared emission at ∼5–3000 μm and ∼0.4% of the total interstellar dust mass.

We present an analysis of the molecular gas properties, based on CO (2−1) emission, of 12 starburst galaxies at z ∼ 1.6 selected by having a boost (≳4×) in their star formation rate (SFR) above the average star-forming galaxy at an equivalent stellar mass. ALMA observations are acquired of six more galaxies than previously reported through our effort. As a result of the larger statistical sample, we significantly detect, for the first time at high z, a systematically lower ${L}_{\mathrm{CO}}^{{\prime} }$/L_IR ratio in galaxies lying above the star-forming "main sequence" (MS). Based on an estimate of α_CO (i.e., the ratio of molecular gas mass to ${L}_{\mathrm{CO}\,1-0}^{{\prime} }$), we convert the observational quantities (e.g., ${L}_{\mathrm{CO}}^{{\prime} }$/L_IR) to physical units (M_gas/SFR) that represent the gas depletion time or its inverse, the star formation efficiency. We interpret the results as indicative of the star formation efficiency increasing in a continuous fashion from the MS to the starburst regime, whereas the gas fractions remain comparable to those of MS galaxies. However, the balance between an increase in star formation efficiency and gas fraction depends on the adopted value of α_CO as discussed.

The purpose of this study is the identification of young (1 < age < 100 Myr), nearby (d ≤ 100 pc) moving groups (YNMGs) through their kinematic signature. YNMGs could be the result of the recent dispersal of young embedded clusters, such that they still represent kinematically cold groups, carrying the residual motion of their parental cloud. Using the fact that a large number (∼14,000) of the RAVE sources with evidence of chromospheric activity also present signatures of stellar youth, we selected a sample of solar-type sources with the highest probability of chromospheric activity to look for common kinematics. We made use of radial velocity information from RAVE and astrometric parameters from GAIA DR2 to construct a 6D position–velocity vector catalog for our full sample. We developed a method based on the grouping of stars with similar orientation of their velocity vectors, which we call the Cone Method Sampling. Using this method, we detected 646 sources with high significance in the velocity space, with respect to the average orientation of artificial distributions made from a purely Gaussian velocity ellipsoid with null vertex deviation. We compared this sample of highly significant sources with a catalog of YNMGs reported in previous studies, which yield 75 confirmed members. From the remaining sample, about 50% of the sources have ages younger than 100 Myr, which indicate they are highly probable candidates to be new members of identified or even other YNMGs in the solar neighborhood.

We present high-resolution (02, 1000 au) 1.3 mm ALMA observations of the massive infrared dark cloud clump, G028.37+00.07-C1, thought to harbor the early stages of massive star formation. Using ${{\rm{N}}}_{2}{{\rm{D}}}^{+}$(3–2), we resolve the previously identified C1-S core, separating the bulk of its emission from two nearby protostellar sources. C1-S is thus identified as a massive (∼50 M_⊙), compact (∼0.1 pc diameter) starless core, e.g., with no signs of outflow activity. Being highly deuterated, this is a promising candidate for a pre-stellar core on the verge of collapse. An analysis of its dynamical state indicates a sub-virial velocity dispersion compared to a trans-Alfvénic turbulent core model. However, virial equilibrium could be achieved with sub-Alfvénic conditions involving magnetic field strengths of ∼2 mG.

We find, using high-resolution numerical relativistic simulations, that the tail of the dynamical ejecta of neutron star mergers extends to mildly relativistic velocities faster than 0.7c. The kinetic energy of this fast tail is ∼10⁴⁷–10⁴⁹ erg, depending on the neutron star equation of state and on the binary masses. The synchrotron flare arising from the interaction of this fast tail with the surrounding interstellar medium (ISM) can power the observed nonthermal emission that followed GW170817, provided that the ISM density is $\sim {10}^{-2}\,{\mathrm{cm}}^{-3}$, the two neutron stars had roughly equal masses and the neutron star equation of state is soft (small neutron star radii). One of the generic predictions of this scenario is that the cooling frequency crosses the X-ray band on a timescale of a few months to a year, leading to a cooling break in the X-ray light curve. While the recent observation of the superluminal motion resolved by very long baseline interferometry (VLBI) rules out the dynamical ejecta scenario, the model described in this paper is generic and can be applied for future neutron star merger events.

We present the results of a Keck/NIRSPEC follow-up survey of 13 late-type T dwarfs (T6–T9), 12 of which have unusually red or blue J − H colors. Previous work suggests that J − H color outliers may represent the high-gravity, low-metallicity (old) and low-gravity, solar-metallicity (young) extremes of the late-type T dwarf population. We use medium-resolution Y- and H-band spectroscopy to probe regions of T dwarf atmospheres that are more sensitive to gravity and metallicity variations than the J band. We find that the spectral morphologies of our sample are largely homogeneous, with peak-normalized, Y- and H-band morphologies consistent with spectral standards. However, three objects stand out as potentially old, with overluminous Y-band spectra compared to their respective spectral standards, and a fourth object stands out as potentially young, with an underluminous Y band. Of these four objects, three have been previously identified as potential metallicity/gravity outliers, including the one object in our sample with a normal J − H color. We fit publicly available atmospheric model grids to our spectra and find that the best-fit physical parameters vary depending on the model used. As we continue to probe the characteristics of the late-T population, differences in synthetic spectra of ∼10%–20% in the blue wing of the Y band and ∼45% at 1.65 μm, for the same physical parameters, must be reconciled. Further development and public availability of nonsolar metallicity models is also recommended. Future progress toward deciphering the impacts of gravity, metallicity, and variability in the late-type T dwarf population will also require high signal-to-noise, multiwavelength and multi-epoch photometry and spectroscopy.

This paper examines the ability to produce a laser beam detectable to a cursory survey (SNR 0.1% with a 1 m receive telescope) by an extraterrestrial intelligence using proven or near-term technology (megawatt-class lasers, telescopes tens of meters in size). We find that such lasers can produce a signal at ranges of less than 20,000 lt-yr, with a broad enough beam to overcome uncertainties in nearby exoplanet orbits (e.g., Prox Cen b) or encompass entire habitable zones of more distant systems (e.g., TRAPPIST-1). While the probability of closing a handshake with even a nearby extraterrestrial intelligence is low with current survey methodologies, advances in full-sky surveys for SETI and other purposes may reduce the mean-time-to-handshake to decades or centuries, after which these laser systems may close links at data rates of kbps–Mpbs. The next major gap to address for searching for extraterrestrial lasers is in expanding spectral searches into the infrared, where most terrestrial communication and high-power lasers are manufactured.

It is unknown whether or not low-mass stars can form at low metallicity. While theoretical simulations of Population III (Pop III) star formation show that protostellar disks can fragment, it is impossible for those simulations to discern if those fragments survive as low-mass stars. We report the discovery of a low-mass star on a circular orbit with orbital period P = 34.757 ± 0.010 days in the ultra metal-poor (UMP) single-lined spectroscopic binary system 2MASS J18082002–5104378. The secondary star 2MASS J18082002–5104378 B has a mass ${M}_{2}={0.14}_{-0.01}^{+0.06}\,{M}_{\odot }$, placing it near the hydrogen-burning limit for its composition. The 2MASS J18082002–5104378 system is on a thin disk orbit as well, making it the most metal-poor thin disk star system by a considerable margin. The discovery of 2MASS J18082002–5104378 B confirms the existence of low-mass UMP stars and its short orbital period shows that fragmentation in metal-poor protostellar disks can lead to the formation and survival of low-mass stars. We use scaling relations for the typical fragment mass and migration time along with published models of protostellar disks around both UMP and primordial composition stars to explore the formation of low-mass Pop III stars via disk fragmentation. We find evidence that the survival of low-mass secondaries around solar-mass UMP primaries implies the survival of solar-mass secondaries around Pop III primaries with masses $10\,{M}_{\odot }\lesssim {M}_{* }\lesssim 100\,{M}_{\odot }$. If true, this inference suggests that solar-mass Pop III stars formed via disk fragmentation could survive to the present day.

The enigmatic near-infrared transient VVV-WIT-06 underwent a large-amplitude eruption of unclear origin in 2013 July. Based on its light curve properties and late-time post-outburst spectra, various possibilities have been proposed in the literature for the origin of the object, namely a Type I supernova, a classical nova (CN), or a violent stellar merger event. We show that, of these possibilities, an origin in a CN outburst convincingly explains the observed properties of VVV-WIT-06. We estimate that the absolute K-band magnitude of the nova at maximum was M_k = −8.2 ± 0.5, its distance d = 13.35 ± 2.18 kpc, and the extinction A_v = 15.0 ± 0.55 mag.

Observations show that winds can be driven from the innermost region (inside a 50 Schwarschild radius) of a thin disk. It is interesting to study the winds launched from the innermost region. A hot corona above the black hole (BH) thin disk is irradiated by the disk. We perform two-dimensional hydrodynamical simulations to study the winds driven by radiation force from the corona in the innermost regions. The hard X-ray spectrum from active galactic nuclei (AGNs) suggests that the corona temperature is about 10⁹ K, so that we mainly analyze the properties of winds (or outflows) from the 10⁹ K corona. The disk luminosity plays an important role in driving the outflows. The more luminous the disk, the stronger the outflows. Mass outflow rate (${\dot{M}}_{\mathrm{out}}$) at a 90 Schwarschild radius depends on disk luminosity, which can be described as ${\dot{M}}_{\mathrm{out}}\propto {10}^{3.3{\rm{\Gamma }}}$ (Γ is the ratio of the disk luminosity to the Eddington luminosity). In the case of high luminosity (e.g., Γ = 0.75), the supersonic outflows with maximum speed 1.0 × 10⁴ Km s⁻¹ are launched at ∼17°–30° and ∼50°–80° away from the pole axis. The Bernoulli parameter keeps increasing with the outward propagation of outflows. The radiation force keeps accelerating the outflows when outflows move outward. Therefore, we can expect the outflows to escape from the BH gravity and go to the galactic scale. The interaction between outflows and interstellar medium may be an important AGN feedback process.

Cold stellar streams—produced by tidal disruptions of globular clusters—are long-lived, coherent dynamical features in the halo of the Milky Way. They hold the promise of delivering precise information about the gravitational potential, including constraints on the shape of the dark matter halo. Because of their different ages and different positions in phase space, different streams tell us different things about the Galaxy. Here we employ a Cramér–Rao lower bound (CRLB) or Fisher-matrix approach to understand the quantitative information content in (toy versions of) 11 known streams: ATLAS, GD-1, Hermus, Kwando, Orinoco, PS1A, PS1C, PS1D, PS1E, Sangarius, and Triangulum. This approach depends on a generative model, which we have developed previously, and which permits calculation of derivatives of predicted stream properties with respect to Galaxy and stream parameters. We find that in simple analytic models of the Milky Way, streams on eccentric orbits contain the most information about the halo shape. For each stream, there are near degeneracies between dark matter halo properties and parameters of the bulge, the disk, and the stream progenitor itself, but simultaneous fitting of multiple streams will constrain all parameters at the percent level. At this precision, simulated dark matter halos deviate from simple analytic parameterizations, so we add an expansion of basis functions as a first step in giving the gravitational potential more freedom. As freedom increases, the information about the halo reduces overall, and it becomes more localized to the current position of the stream. In the limit of high model freedom, a stellar stream appears to measure the local acceleration at its current position; this motivates thinking about future nonparametric approaches. The CRLB formalism also permits us to assess the value of future measurements of stellar velocities, distances, and proper motions. We show that velocities of stream stars are essential for producing competitive constraints on the distribution of dark matter.

We use a suite of cosmological zoom galaxy formation simulations and dust radiative transfer calculations to explore the use of the monochromatic 850 μm luminosity (L_ν,850) as a molecular gas mass (M_mol) estimator in galaxies between 0 < z < 9.5 for a broad range of masses. For our fiducial simulations, where we assume that the dust mass is linearly related to the metal mass, we find that empirical L_ν,850–M_mol calibrations accurately recover the molecular gas mass of our model galaxies and that the L_ν,850-dependent calibration is preferred. We argue that the major driver of scatter in the L_ν,850–M_mol relation arises from variations in the molecular gas-to-dust mass ratio, rather than variations in the dust temperature, in agreement with the previous study of Liang et al. Emulating a realistic measurement strategy with ALMA observing bands that are dependent on the source redshift, we find that estimating S_ν,850 from continuum emission at a different frequency contributes 10%–20% scatter to the L_ν,850–M_mol relation. This additional scatter arises from a combination of mismatches in assumed T_dust and β values, as well as the fact that the SEDs are not single-temperature blackbodies. However, this observationally induced scatter is a subdominant source of uncertainty. Finally, we explore the impact of a dust prescription in which the dust-to-metals ratio varies with metallicity. Though the resulting mean dust temperatures are ∼50% higher, the dust mass is significantly decreased for low-metallicity halos. As a result, the observationally calibrated L_ν,850–M_mol relation holds for massive galaxies, independent of the dust model, but below L_ν,850 ≲ 10²⁸ erg s⁻¹ (metallicities ${\mathrm{log}}_{10}(Z/{Z}_{\odot })\lesssim -0.8$) we expect that galaxies may deviate from literature observational calibrations by ≳0.5 dex.

The discovery of an ultrafast outflow has been reported in the z = 0.0658 narrow-line Seyfert galaxy IRAS 13224−3809. The ultrafast outflow was first inferred through the detection of highly blueshifted absorption lines and then confirmed with a principal component analysis. Two of the reported properties of this outflow differed from those typically detected in other AGNs with ultrafast outflows. First, the outflow velocity was found not to vary with v = 0.236c ± 0.006c. Second, the equivalent width of the highly blueshifted absorption line was reported to be anticorrelated with the 3–10 keV flux of this source. We present a reanalysis of the XMM-Newton observations of IRAS 13224−3809 considering the influence of background. We also undertook a different analysis approach in combining the spectra and investigated the change of the properties of the outflow as a function of 3–10 keV flux and time. We confirm the presence of an ultrafast outflow in IRAS 13224−3809; however, we find that the background spectra used in the Parker et al. analyses dominate the source spectra for energies near the blueshifted iron lines. By reducing the source extraction regions to improve the signal-to-noise ratio, we discover larger than previously reported outflow velocities and find that the outflow velocity varies from ∼0.2c to ∼0.3c and increases with 3–10 keV flux. The previously reported anticorrelation between equivalent width of the iron line and 3–10 keV flux disappears when the background spectra are reduced by optimizing the source extraction regions.

The 2D model of the field line random walk (FLRW) is developed by considering a space-dependent mean magnetic field ${B}_{0z}{{\boldsymbol{e}}}_{z}$ with perpendicular and parallel gradients, and a component in the perpendicular plane ${{\boldsymbol{B}}}_{0\perp }.$ The impact of the configuration of the mean field on FLRW is explored. We have found that both the diffusion (random walk) and the convection (ordered walk) are significantly modified. The diffusion is strongly influenced by the parallel gradient and by ${{\boldsymbol{B}}}_{0\perp }$, while the perpendicular gradient generates a flow of the field lines along its direction. A synergistic effect between the three elements of the configuration of the mean field is found.

The Asteroid Terrestrial-impact Last Alert System (ATLAS) observes most of the sky every night in search of dangerous asteroids. Its data are also used to search for photometric variability, where sensitivity to variability is limited by photometric accuracy. Since each exposure spans 76 corner to corner, variations in atmospheric transparency in excess of 0.01 mag are common, and 0.01 mag photometry cannot be achieved by using a constant flat-field calibration image. We therefore have assembled an all-sky reference catalog of approximately one billion stars to m ∼ 19 from a variety of sources to calibrate each exposure's astrometry and photometry. Gaia DR2 is the source of astrometry for this ATLAS Refcat2. The sources of g, r, i, and z photometry include Pan-STARRS DR1, the ATLAS Pathfinder photometry project, ATLAS reflattened APASS data, SkyMapper DR1, APASS DR9, the Tycho-2 catalog, and the Yale Bright Star Catalog. We have attempted to make this catalog at least 99% complete to m < 19, including the brightest stars in the sky. We believe that the systematic errors are no larger than 5 mmag rms, although errors are as large as 20 mmag in small patches near the Galactic plane.

Luminous red galaxies (LRGs) are the most massive galaxies at z ∼ 0.5 and, by selection, have negligible star formation (SF). These objects have halo masses between those of L_* galaxies, whose circumgalactic media (CGMs) are observed to have large masses of cold gas, and clusters of galaxies, which primarily contain hot gas. Here, we report detections of strong and extended metal (C iii 977) and H i lines in the CGM of two LRGs. The C iii lines have equivalent widths (EWs) of ∼1.8 and ∼1.2 Å, and velocity spreads of ∼796 and ∼1245 $\mathrm{km}\,{{\rm{s}}}^{-1}$, exceeding all such measurements from local ∼L_* galaxies (maximal C iii EWs ∼1 Å). The data demonstrate that a subset of halos hosting very massive, quenched galaxies contain significant complexes of cold gas. Possible scenarios to explain our observations include that the LRGs' CGMs originate from past activity (e.g., SF or active galactic nuclei driven outflows) or from the CGMs of galaxies in overlapping subhalos. We favor the latter scenario, in which the properties of the CGMs are more tightly linked to the underlying dark matter halo than properties of the targeted galaxies (e.g., SF).

We investigate the local and line-of-sight (LOS) overdensities of strong gravitational lens galaxies using wide-area multiband imaging from the Hyper Suprime-Cam Subaru Strategic Program. We present 41 new definite or probable lens candidates discovered in Data Release 2 of the survey. Using a combined sample of 87 galaxy-scale lenses out to a lens redshift of z_L ∼ 0.8, we compare galaxy number counts in LOSs toward known and newly discovered lenses in the survey to those of a control sample consisting of random LOSs. We also compare the local overdensity of lens galaxies to a sample of "twin" galaxies that have similar redshift and velocity dispersion to test whether lenses lie in different environments from similar nonlens galaxies. We find that lens fields contain higher number counts of galaxies compared to the control fields, but this effect arises from the local environment of the lens. Once galaxies in the lens plane are removed, the lens LOSs are consistent with the control sample. The local environments of the lenses are overdense compared to the control sample, and are slightly overdense compared to those of the twin sample, although the significance is marginal. There is no significant evidence of the evolution of the local overdensity of lens environments with redshift.

Recent analyses suggest that distance residuals measured from Type Ia supernovae (SNe Ia) are correlated with local host galaxy properties within a few kiloparsecs of the SN explosion. However, the well-established correlation with global host galaxy properties is nearly as significant, with a shift of 0.06 mag across a low to high mass boundary (the mass step). Here, with 273 SNe Ia at z < 0.1, we investigate whether the stellar masses and rest-frame u − g colors of regions within 1.5 kpc of the SN Ia explosion site are significantly better correlated with SN distance measurements than global properties or properties measured at random locations in SN hosts. At ≲2σ significance, local properties tend to correlate with distance residuals better than properties at random locations, though despite using the largest low-z sample to date, we cannot definitively prove that a local correlation is more significant than a random correlation. Our data hint that SNe observed by surveys that do not target a pre-selected set of galaxies may have a larger local mass step than SNe from surveys that do, an increase of 0.071 ± 0.036 mag (2.0σ). We find a 3σ local mass step after global mass correction, evidence that SNe Ia should be corrected for their local mass, but we note that this effect is insignificant in the targeted low-z sample. Only the local mass step remains significant at >2σ after global mass correction, and we conservatively estimate a systematic shift in H₀ measurements of −0.14 km s⁻¹ Mpc⁻¹ with an additional uncertainty of 0.14 km s⁻¹ Mpc⁻¹, ∼10% of the present uncertainty.

Y dwarfs provide a unique opportunity to study free-floating objects with masses <30 M_Jup and atmospheric temperatures approaching those of known Jupiter-like exoplanets. Obtaining distances to these objects is an essential step toward characterizing their absolute physical properties. Using Spitzer's Infrared Array Camera (IRAC) [4.5] images taken over baselines of ∼2–7 years, we measure astrometric distances for 22 late-T and early Y dwarfs, including updated parallaxes for 18 objects and new parallax measurements for 4 objects. These parallaxes will make it possible to explore the physical parameter space occupied by the coldest brown dwarfs. We also present the discovery of six new late-T dwarfs, updated spectra of two T dwarfs, and the reclassification of a new Y dwarf, WISE J033605.04−014351.0, based on Keck/NIRSPEC J-band spectroscopy. Assuming that effective temperatures are inversely proportional to absolute magnitude, we examine trends in the evolution of the spectral energy distributions of brown dwarfs with decreasing effective temperature. Surprisingly, the Y dwarf class encompasses a large range in absolute magnitude in the near- to mid-infrared photometric bandpasses, demonstrating a larger range of effective temperatures than previously assumed. This sample will be ideal for obtaining mid-infrared spectra with the James Webb Space Telescope because their known distances will make it easier to measure absolute physical properties.

We present a broadband X-ray spectral analysis of the M51 system, including the dual active galactic nuclei (AGNs) and several off-nuclear point sources. Using a deep observation by NuSTAR, new high-resolution coverage of M51b by Chandra, and the latest X-ray torus models, we measure the intrinsic X-ray luminosities of the AGNs in these galaxies. The AGN of M51a is found to be Compton-thick, and both AGNs have very low accretion rates (${\lambda }_{\mathrm{Edd}}\lt {10}^{-4}$). The latter is surprising considering that the galaxies of M51 are in the process of merging, which is generally predicted to enhance nuclear activity. We find that the covering factor of the obscuring material in M51a is 0.26 ± 0.03, consistent with the local AGN obscured fraction at ${L}_{{\rm{X}}}$$\sim {10}^{40}$ erg s⁻¹. The substantial obscuring column does not support theories that the torus, presumed responsible for the obscuration, disappears at these low accretion luminosities. However, the obscuration may have resulted from the gas infall driven by the merger rather than the accretion process. We report on several extranuclear sources with ${L}_{{\rm{X}}}$$\gt {10}^{39}$ erg s⁻¹ and find that a spectral turnover is present below 10 keV in most such sources, in line with recent results on ultraluminous X-ray sources.

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of ¹²CO(1–0) and ¹²CO(2–1) in the central 40'' (680 pc) of the nuclear starburst galaxy NGC 253, including its molecular outflow. We measure the ratio of brightness temperature for CO(2–1)/CO(1–0), r₂₁, in the central starburst and outflow-related features. We discuss how r₂₁ can be used to constrain the optical depth of the CO emission, which impacts the inferred mass of the outflow and consequently the molecular mass outflow rate. We find r₂₁ ≲ 1 throughout, consistent with a majority of the CO emission being optically thick in the outflow, as it is in the starburst. This suggests that the molecular outflow mass is 3–6 times larger than the lower limit reported for optically thin CO emission from warm molecular gas. The implied molecular mass outflow rate is 25–50 M_⊙ yr⁻¹, assuming that the conversion factor for the outflowing gas is similar to our best estimates for the bulk of the starburst. This is a factor of 9–19 times larger than the star formation rate in NGC 253. We see tentative evidence for an extended, diffuse CO(2–1) component.

Methods to solve the relativistic hydrodynamic equations are important in a large number of astrophysical simulations, which may be very dynamic and involve multiscale features. This requires computational methods that are highly adaptive and capable of automatically resolving numerous localized features and instabilities that emerge across the computational domain and over many temporal scales. While this has been historically accomplished with adaptive-mesh-refinement-based methods, alternatives using wavelet bases and the wavelet transformation have recently achieved significant success in adaptive representation for advanced engineering applications. The current work presents a new method, extending the wavelet adaptive multiresolution representation method, for the integration of the relativistic hydrodynamic equations using iterated interpolating wavelets and introduces a highly adaptive implementation for multidimensional simulation. The wavelet coefficients provide a direct measure of the local approximation error for the solution and place collocation points that naturally adapt to the fluid flow while providing good conservation of fluid quantities. The resulting implementation, oahu, is applied to a series of demanding 1D and 2D problems that explore high Lorentz factor outflows and the formation of several instabilities, including the Kelvin–Helmholtz instability and the Rayleigh–Taylor instability.

The energy liberated by fallback accretion has been suggested as a possible engine to power hydrogen-poor superluminous supernovae (SLSNe). We systematically investigate this model using the Bayesian light curve (LC) fitting code MOSFiT (Modular Open Source Fitter for Transients), fitting the LCs of 37 hydrogen-poor SLSNe assuming a fallback accretion central engine. We find that this model can yield good fits to their LCs, with a fit quality that rivals the popular magnetar engine models. Examining our derived parameters for the fallback model, we estimate the total energy requirements from the accretion disk to be 0.002–0.7 ${\text{}}{M}_{\odot }$c². If we adopt a typical conversion efficiency ∼10⁻³, the required mass to accrete is thus 2–700 ${\text{}}{M}_{\odot }$. Many SLSNe, therefore, require an unrealistic accretion mass, and so only a fraction of these events could be powered by fallback accretion unless the true efficiency is much greater than our fiducial value. The SLSNe that require the smallest amounts of fallback mass are still fallback accretion-powered supernova candidates, but they are difficult to distinguish solely by their LC properties.

We report on the results of optical, near-infrared (NIR), and mid-infrared observations of the black hole X-ray binary candidate (BHB) MAXI J1535–571 during its 2017/2018 outburst. During the first part of the outburst (MJD 58004–58012), the source shows an optical–NIR spectrum that is consistent with an optically thin synchrotron power law from a jet. After MJD 58015, however, the source faded considerably, the drop in flux being much more evident at lower frequencies. Before the fading, we measure a dereddened flux density of ≳100 mJy in the mid-infrared, making MAXI J1535–571 one of the brightest mid-infrared BHBs known so far. A significant softening of the X-ray spectrum is evident contemporaneous with the infrared fade. We interpret it as being due to the suppression of the jet emission, similar to the accretion–ejection coupling seen in other BHBs. However, MAXI J1535–571 did not transition smoothly to the soft state, instead showing X-ray hardness deviations associated with infrared flaring. We also present the first mid-IR variability study of a BHB on minute timescales, with a fractional rms variability of the light curves of ∼15%–22%, which is similar to that expected from the internal shock jet model, and much higher than the optical fractional rms (≲7%). These results represent an excellent case of multiwavelength jet spectral timing and demonstrate how rich, multiwavelength time-resolved data of X-ray binaries over accretion state transitions can help in refining models of the disk–jet connection and jet launching in these systems.

We construct a new 3D Whole-prominence Fine-structure (WPFS) model based on a prominence magnetic field configuration designed to qualitatively approximate the morphology of a quiescent prominence observed on 2010 June 22. The model represents an entire prominence with its numerous fine structures formed by a prominence plasma located in dips in the prominence magnetic field. We use the constructed 3D model and employ a radiative-transfer-based Hα visualization method to analyze the Hα visibility of prominence fine structures and its effect on the perceived morphology of observed and modeled prominences. We qualitatively compare three techniques used for visualization of modeled prominences—visualizations drawing magnetic dips up to a height of 1 pressure scale height, drawing the full extent of magnetic dips, and the synthetic Hα visualization—and discuss their suitability for direct comparison between models and observations of prominences and filaments. We also discuss the role of visibility of the prominence fine structures in the estimation of the total height of prominences, which may indicate the height of pre-erupting flux ropes. This parameter is critical for the observational determination of the flux-rope stability. In addition, we employ the WPFS model to assess the effects caused by a projection of the naturally three-dimensional and heterogeneous prominences onto a two-dimensional plane of the sky. We discuss here how the morphological structures of prominences differ when observed in projections from different viewing angles. We also discuss the shapes of the dipped magnetic field lines and the perceived projection of motions of prominence fine structures along such field lines.

We present a detailed study of the disk around the intermediate-mass star SO 411, aiming to explain the spectral energy distribution of this star. We show that this is a transitional disk truncated at ∼11 au, with ∼0.03 lunar masses of optically thin dust inside the cavity. Gas also flows through the cavity, since we find that the disk is still accreting mass onto the star, at a rate of ∼5 × 10⁻⁹M_☉ yr⁻¹. Until now, SO 411 has been thought to belong to the ∼3 Myr old σ Orionis cluster. However, we analyzed the second Gaia Data Release in combination with kinematic data previously reported and found that SO 411 can be associated with a sparse stellar population located in front of the σ Orionis cluster. If this is the case, then SO 411 is older and even more peculiar, since primordial disks in this stellar mass range are scarce for ages >5 Myr. Analysis of the silicate 10 μm feature of SO 411 indicates that the observed feature arises at the edge of the outer disk and displays a very high crystallinity ratio of ∼0.5, with forsterite the most abundant silicate crystal. The high forsterite abundance points to crystal formation in nonequilibrium conditions. The PAH spectrum of SO 411 is consistent with this intermediate state between the hot and luminous Herbig Ae and the less massive and cooler T Tauri stars. Analysis of the 7.7 μm PAH feature indicates that small PAHs still remain in the SO 411 disk.

We present a high-sensitivity (1σ < 1.6 mJy beam⁻¹) continuum observation in a 343 arcmin² area of the northeast region of the Small Magellanic Cloud at a wavelength of 1.1 mm, conducted using the AzTEC instrument on the ASTE telescope. In the observed region, we identified 20 objects by contouring 10σ emission. Through spectral energy distribution analysis using 1.1 mm, Herschel, and Spitzer data, we estimated gas masses of 5 × 10³–7 × 10⁴M_⊙, assuming a gas-to-dust ratio of 1000. The dust temperature and index of emissivity were also estimated as 18–33 K and 0.9–1.9, respectively, which are consistent with previous low-resolution studies. The dust temperature and the index of emissivity shows a weak negative linear correlation. We also investigated five CO-detected, dust-selected clouds in detail. The total gas masses were comparable to those estimated from the Mopra CO data, indicating that the assumed gas-to-dust ratio of 1000 and the X_CO factor of 1 × 10²¹ cm⁻² (K km s⁻¹)⁻¹, with uncertainties of a factor of 2, are reliable for the estimation of the gas masses of molecular or dust-selected clouds. The dust column density showed good spatial correlation with CO emission, except for an object associated with bright young stellar objects. The 8 μm filamentary and clumpy structures also showed a spatial distribution similar to that of the CO emission and dust column density, supporting the fact that polycyclic aromatic hydrocarbon emissions arise from the surfaces of dense gas and dust clouds.

We use both photometric and spectroscopic data from the Hubble Space Telescope to explore the relationships among 4000 Å break (D4000) strength, colors, stellar masses, and morphology, in a sample of 352 galaxies with log(M_*/M_⊙) > 9.44 at 0.6 ≲ z ≲ 1.2. We have identified authentically quiescent galaxies in the UVJ diagram based on their D4000 strengths. This spectroscopic identification is in good agreement with their photometrically derived specific star formation rates (sSFRs). Morphologically, most (that is, 66 out of 68 galaxies, ∼97%) of these newly identified quiescent galaxies have a prominent bulge component. However, not all of the bulge-dominated galaxies are quenched. We found that bulge-dominated galaxies show positive correlations among the D4000 strength, stellar mass, and Sérsic index, while late-type disks do not show such strong positive correlations. Also, bulge-dominated galaxies are clearly separated into two main groups in the parameter space of sSFR versus stellar mass and stellar surface density within the effective radius, Σ_e, while late-type disks and irregulars only show high sSFR. This split is directly linked to the "blue cloud" and the "red sequence" populations and correlates with the associated central compactness indicated by Σ_e. While star-forming massive late-type disks and irregulars (with D4000 < 1.5 and log(M_*/M_⊙) ≳ 10.5) span a stellar mass range comparable to bulge-dominated galaxies, most have systematically lower Σ_e ≲ 10⁹M_⊙ kpc⁻². This suggests that the presence of a bulge is a necessary but not sufficient requirement for quenching at intermediate redshifts.

We present a semi-analytic model for self-consistently evolving a population of globular clusters (GCs) in a given host galaxy across cosmic time. We compute the fraction of GCs still hosting intermediate-mass black holes (IMBHs) at a given redshift in early and late -type galaxies of different masses and sizes, and the corresponding rate of tidal disruption events (TDEs), both main-sequence (MS) and white dwarf (WD) stars. We find that the integrated TDE rate for the entire GC population can exceed the corresponding rate in a given galactic nucleus and that ∼90% of the TDEs reside in GCs within a maximum radius of ∼2–15 kpc from the host galaxy's center. This suggests that observational efforts designed to identify TDEs should not confine themselves to galactic nuclei alone, but should also consider the outer galactic halo where massive old GCs hosting IMBHs would reside. Indeed, such off-center TDEs as predicted here may already have been observed. MS TDE rates are more common than WD TDE rates by a factor of 30 (100) at z ≤ 0.5 (z = 2). We also calculate the rate of IMBH-SBH mergers across cosmic time, finding that the typical IMRI rate at low redshift is of the order of ∼0.5–3 Gpc⁻³ yr⁻¹, which becomes as high as ∼100 Gpc⁻³ yr⁻¹ near the peak of GC formation. Advanced LIGO, combined with VIRGO, KAGRA, the Einstein Telescope, and LISA will be able to observe the bottom end and top end of the IMBH population.

We investigate the electron–positron pair cascade taking place in the magnetosphere of a rapidly rotating black hole. Because of the spacetime frame dragging, the Goldreich–Julian charge density changes sign in the vicinity of the event horizon, which leads to the occurrence of a magnetic-field-aligned electric field, in the same way as the pulsar outer-magnetospheric accelerator. In this lepton accelerator, electrons and positrons are accelerated in the opposite directions, to emit copious gamma rays via the curvature and inverse Compton processes. We examine a stationary pair cascade and show that a stellar-mass black hole moving in a gaseous cloud can emit a detectable very high energy flux, provided that the black hole is extremely rotating and that the distance is less than about 1 kpc. We argue that the gamma-ray image will have a point-like morphology, and we demonstrate that their gamma-ray spectra have a broad peak around 0.01–1 GeV and a sharp peak around 0.1 TeV, that the accelerators become most luminous when the mass accretion rate becomes about 0.01% of the Eddington rate, and that the predicted gamma-ray flux changes little in a wide range of magnetospheric currents. An implication of the stability of such a stationary gap is discussed.

Cepheid stars play a considerable role as extragalactic distances indicators, thanks to the simple empirical relation between their pulsation period and their luminosity. They overlap with that of secondary distance indicators, such as Type Ia supernovae, whose distance scale is tied to Cepheid luminosities. However, the period–luminosity (P–L) relation still lacks a calibration to better than 5%. Using an original combination of interferometric astrometry with optical and ultraviolet spectroscopy, we measured the geometrical distance $d=720.35\pm 7.84$ pc of the 3.33 day period Cepheid V1334 Cyg with an unprecedented accuracy of ±1%, providing the most accurate distance for a Cepheid. Placing this star in the P–L diagram provides an independent test of existing P–L relations. We show that the secondary star has a significant impact on the integrated magnitude, particularly at visible wavelengths. Binarity in future high-precision calibrations of the P–L relations is not negligible, at least in the short-period regime. Subtracting the companion flux leaves V1334 Cyg in marginal agreement with existing photometric-based P–L relations, indicating either an overall calibration bias or a significant intrinsic dispersion at a few percent level. Our work also enabled us to determine the dynamical masses of both components, ${M}_{1}=4.288\pm 0.133\,{M}_{\odot }$ (Cepheid) and ${M}_{2}=4.040\pm 0.048\,{M}_{\odot }$ (companion), providing the most accurate masses for a Galactic binary Cepheid system.

Recent detections of high-energy γ-rays from behind-the-limb (BTL) solar flares by the Fermi Gamma-ray Space Telescope pose a puzzle and challenge on the particle acceleration and transport mechanisms. In such events, the γ-ray emission region is located away from the BTL flare site by up to tens of degrees in heliographic longitude. It is thus hypothesized that particles are accelerated at the shock driven by the coronal mass ejection (CME) and then travel from the shock downstream back to the front side of the Sun to produce the observed γ-rays. To test this scenario, we performed data-driven, global magnetohydrodynamics simulations of the CME associated with a well-observed BTL flare on 2014 September 1. We found that part of the CME-driven shock develops magnetic connectivity with the γ-ray emission region, facilitating transport of particles back to the Sun. Moreover, the observed increase in γ-ray flux is temporally correlated with (1) the increase of the shock compression ratio and (2) the presence of a quasi-perpendicular shock over the area that is magnetically connected to the γ-ray emitting region, both conditions favoring the diffusive shock acceleration (DSA) of particles. These results support the above hypothesis and can help resolve another puzzle, i.e., long-duration (up to 20 hr) γ-rays flares. We suggest that, in addition to DSA, stochastic acceleration by plasma turbulence may also play a role, especially in the shock downstream region and during the early stage when the shock Alfvén Mach number is small.

When mobilized, granular materials become charged as grains undergo collisions and frictional interactions. On Earth, this process, known as triboelectrification, has been recognized in volcanic plumes and sandstorms. Yet, frictional charging almost certainly exists on other worlds, both in our own solar system (such as Mars, the Moon, and Venus) and exosolar planets. Indeed, observations suggest that numerous planets in the galaxy are enshrouded by optically thick clouds or hazes. Triboelectric charging within these clouds may contribute to global electric circuits of these worlds, providing mechanisms to generate lightning, drive chemical processes in the atmospheres, and, perhaps, influence habitability. In this work, we explore the frictional electrification of potassium chloride and zinc sulfide, two substances proposed to make up the clouds of giant exoplanets with >50× solar metallicities, including the widely studied super-Earth GJ 1214b, super-Earth HD 97658b, Neptune-sized GJ 436b, and hot-Jupiter WASP-31b. We find that both materials become readily electrified when mobilized, attaining charge densities similar to those found on volcanic ash particles. Thus, if these worlds do indeed host collections of mineral particles in their atmospheres, these clouds are likely electrified and may be capable of producing lightning or corona discharge.

In this work we focus on a group of Galactic double neutron star (DNS) systems with long orbital periods of ≳1 day and low eccentricities of ≲0.4. The feature of these orbital parameters is used to constrain the evolutionary processes of progenitor binaries and the supernova (SN) kicks of the second born NSs. Adopting that the mass transfer during primordial binary evolution is highly nonconservative (rotation-dependent), the formation of DNS systems involves a double helium star binary phase, the common envelope (CE) evolution initiates before the first NS formation. During the CE evolution the binary orbital energy is obviously larger when using a helium star rather than an NS to expel the donor envelope, this can help explain the formation of DNS systems with long periods. SN kicks at NS birth can lead to eccentric orbits and even the disruption of binary systems, and the low eccentricities require that the DNSs receive a small natal kick at the second collapse. Compared with the overall distribution of orbital parameters for observed DNS binaries, we propose that the second born NSs in most DNS systems are subject to small natal kicks with the Maxwellian dispersion velocity of less than 80 km s⁻¹, which can provide some constraints on the SN explosion processes. The mass distribution of DNS binaries is also briefly discussed. We suggest that the rotation-dependent mass transfer mode and our results about SN kicks should be applied to massive binary evolution and population synthesis studies.

Populations of massive stars are directly reflective of the physics of stellar evolution. Counts of subtypes of massive stars and ratios of massive stars in different evolutionary states have been used ubiquitously as diagnostics of age and metallicity effects. While the binary fraction of massive stars is significant, inferences are often based upon models incorporating only single-star evolution. In this work, we utilize custom synthetic stellar populations from the Binary Population and Stellar Synthesis code to determine the effect of stellar binaries on number count ratios of different evolutionary stages in both young massive clusters and galaxies with massive stellar populations. We find that many ratios are degenerate in metallicity, age, and/or binary fraction. We develop diagnostic plots using these stellar count ratios to help break this degeneracy, and use these plots to compare our predictions to observed data in the Milky Way and the Local Group. These data suggest a possible correlation between the massive star binary fraction and metallicity. We also examine the robustness of our predictions in samples with varying levels of completeness. We find including binaries and imposing a completeness limit can both introduce ≳0.1 dex changes in inferred ages. Our results highlight the impact that binary evolution channels can have on the massive star population.

Recent core-collapse supernova (CCSN) simulations have predicted several distinct features in gravitational-wave (GW) spectrograms, including a ramp-up signature due to the g-mode oscillation of the protoneutron star (PNS) and an excess in the low-frequency domain (100 to ∼300 Hz) potentially induced by the standing accretion shock instability (SASI). These predictions motivated us to perform a sophisticated time–frequency analysis (TFA) of the GW signals, aimed at preparation for future observations. By reanalyzing a gravitational waveform obtained in a three-dimensional general-relativistic CCSN simulation, we show that both the spectrogram with an adequate window and the quadratic TFA separate the multimodal GW signatures much more clearly compared with a previous analysis. We find that the observed low-frequency excess during the SASI active phase is divided into two components, a stronger one at 130 Hz and an overtone at 260 Hz, both of which evolve quasistatically during the simulation time. We also identify a new mode with frequency varying from 700 to 600 Hz. Furthermore, we develop the quadratic TFA for the Stokes I, Q, U, and V parameters as a new tool to investigate the circular polarization of GWs. We demonstrate that the polarization states that randomly change with time after bounce are associated with the PNS g-mode oscillation, whereas a slowly changing polarization state in the low-frequency domain is connected to the PNS core oscillation. This study demonstrates the capability of sophisticated TFA to diagnose polarized CCSN GWs in order to explore their complex nature.

The core-accretion model predicts that planetary cores as massive as super-Earths undergo runaway gas accretion to become gas giants. However, the exoplanet census revealed the prevalence of super-Earths close to their host stars, which should have avoided runaway gas accretion. In fact, mass–radius relationships of transiting planets suggest that some close-in super-Earths possess H₂/He atmospheres of ∼0.1%–10% by mass. Previous studies indicated that properties of a disk gas such as metallicity and the inflow/outflow cycle of a disk gas around a super-Earth can regulate accumulation of an H₂/He atmosphere onto itself. In this paper, we propose a new mechanism for which radial mass accretion in a disk can limit the gas accretion onto super-Earth cores. Recent magnetohydrodynamic simulations found that magnetically driven disk winds can drive a rapid gas flow near the disk surface. Such a rapid gas flow may slip out of a planetary core and regulate gas supply to an accreting gas onto the core. We performed N-body simulations for formation of super-Earths with accretion of atmospheres in a viscous accretion disk including effects of wind-driven accretion. We found that even super-Earth cores can avoid triggering runaway gas accretion if the inflow of a disk gas toward the cores is limited by viscous accretion. Our model predicts that super-Earths having an H₂/He atmosphere of ∼0.1–10 wt% form within ≲1 au of the central star, whereas gas giants are born in the outer region. This mechanism can explain the radial dependence of observed giant planets beyond the solar system.

We report the results of monitoring of the radio galaxy 3C 120 with the Neil Gehrels Swift Observatory, Very Long Baseline Array, and Metsähovi Radio Observatory. The UV-optical continuum spectrum and R-band polarization can be explained by a superposition of an inverted-spectrum source with a synchrotron component containing a disordered magnetic field. The UV-optical and X-ray light curves include dips and flares, while several superluminal knots appear in the parsec-scale jet. The recovery time of the second dip was longer at UV-optical wavelengths, in conflict with a model in which the inner accretion disk (AD) is disrupted during a dip and then refilled from outer to inner radii. We favor an alternative scenario in which occasional polar alignments of the magnetic field in the disk and corona cause the flux dips and formation of shocks in the jet. Similar to observations of Seyfert galaxies, intra-band time lags of flux variations are longer than predicted by the standard AD model. This suggests that scattering or some other reprocessing occurs. The 37 GHz light curve is well-correlated with the optical-UV variations, with a ∼20 day delay. A radio flare in the jet occurred in a superluminal knot 0.14 milliarcseconds downstream of the 43 GHz "core," which places the site of the preceding X-ray/UV/optical flare within the core 0.5–1.3 pc from the black hole. The inverted UV-optical flare spectrum can be explained by a nearly monoenergetic electron distribution with energy similar to the minimum energy inferred in the TeV γ-ray emitting regions of some BL Lacertae objects.

Solar Cycle 24 has been proven to be the weakest cycle in solar activity in the last century. So far, most of the evidence has been presented near Earth at 1 au. In this study, we statistically studied the magnetic field of the solar wind near Venus and the induced magnetosphere of Venus using Pioneer Venus Orbiter (PVO) and Venus Express (VEX) observations. Our study provides fundamental and comparative results between different solar phases of Solar Cycle 24 at 0.72 au. The solar wind magnetic field strength near Venus shows a strongly correlated variation with solar activities. While the solar wind magnetic field direction, indicated by the B_x component ratio, is almost the same in different solar phases of the same cycle. It is significantly different between Cycle 24 and previous cycles. The magnetic field strength of the Venusian-induced magnetosphere is also closely correlated to solar activities. It is strongest at solar maximum and weakest at solar minimum. Observations from PVO and VEX clearly show that the magnetic barrier of the Venusian-induced magnetosphere is much weaker in Cycle 24 than in previous cycles. But the average magnetic fields of the ionosphere and the magnetotail are stronger in Cycle 24.

According to the traditional scenario for core-collapse supernovae, the core of the collapsing star forms a neutron star (NS) and its gravitational energy release sends out a shock wave into the stellar envelope. However, in a significant number of numerical simulations, the shock stalls and the star cannot be exploded successfully, especially for a massive, compact star. We consider an alternative scenario in which, with mass fallback, the collapsing star forms a black hole in the center, surrounded by a dense, hot accretion disk, which blows out an intense outflow (wind). The kinetic energy of the wind may result in a successful stellar explosion. With an improved version of the formalism in Kohri et al., who studied NS accretion of minor fallback, we study this disk wind-driven explosion by calculating the accretion history for a suite of pre-SN stellar models with different initial surface rotational velocities, masses and metallicities, and by comparing the disk wind energy with the binding energy of the infalling stellar envelope. We show that the most promising models to be exploded successfully by this new channel are those relatively compact pre-SN stars with relatively low metallicities and not too low specific angular momenta. The total energies of the explosions are ∼10^51–52 erg, and a more massive progenitor may produce a more energetic explosion.

We report the identification of blazar candidates behind the Magellanic Clouds. The objects were selected from the Magellanic Quasars Survey (MQS), which targeted the entire Large Magellanic Cloud (LMC) and 70% of the Small Magellanic Cloud (SMC). Among the 758 MQS quasars and 898 of the unidentified (featureless spectra) objects, we identified a sample of 44 blazar candidates, including 27 flat-spectrum radio quasars and 17 BL Lacertae objects, respectively. All the blazar candidates from our sample were identified with respect to their radio, optical, and midinfrared properties. The newly selected blazar candidates possess the long-term, multicolor photometric data from the Optical Gravitational Lensing Experiment, multicolor midinfrared observations, and archival radio data for one frequency at least. In addition, for nine of them, the radio polarization data are available. With such data, these objects can be used to study the physics behind the blazar variability detected in the optical and midinfrared bands, as a tool to investigate magnetic field geometry of the LMC and SMC, and as an exemplary sample of point-like sources most likely detectable in the γ-ray range with the newly emerging Cherenkov Telescope Array.

Using parallaxes from Gaia Data Release 2 (Gaia DR2), we estimate the distance to the globular clusters 47 Tuc and NGC 362, taking advantage of the background stars in the Small Magellanic Cloud and quasars to account for various parallax systematics. We found the parallax to be dependent on the Gaia DR2 G-band apparent magnitude for stars with 13 < G < 18, where brighter stars have a lower parallax zero point than fainter stars. The distance to 47 Tuc was found to be 4.45 ± 0.01 ± 0.12 kpc, and for NGC 362 8.54 ± 0.20 ± 0.44 kpc, with random and systematic errors listed, respectively. This is the first time a precise distance measurement directly using parallaxes has been determined for either of these two globular clusters.

Using atomistic simulations, we characterize the adsorption process of organic molecules on carbon nanoparticles, both of which have been reported to be abundant in the interstellar medium (ISM). The aromatic organics are found to adsorb more readily than the aliphatic ones. This selectivity would favor the formation of polycyclic aromatic hydrocarbons (PAHs) or fullerene-like structures in the ISM due to a structural similarity. In our simulations, we also observed that the molecules form a monolayer over the nanoparticle surface before stacking up in aggregates. This suggests a possible layer-by-layer formation process of onion-like nanostructures in the ISM. These findings reveal the possible role of carbon nanoparticles as selective catalysts that could provide reaction substrates for the formation of interstellar PAHs, high fullerenes, and soots from gas-phase molecules.

The density distribution of flare loops and the mechanisms of their emission in the continuum are still open questions. On 2017 September 10, a prominent loop system appeared during the gradual phase of an X8.2 flare (SOL2017-09-10), visible in all passbands of SDO/AIA and in the white-light continuum of SDO/HMI. We investigate its electron density by taking into account all radiation processes in the flare loops, i.e., the Thomson continuum, hydrogen Paschen and Brackett recombination continua, as well as free–free continuum emission. We derive a quadratic function of the electron density for a given temperature and effective loop thickness. By absolutely calibrating SDO/HMI intensities, we convert the measured intensities into electron density at each pixel in the loops. For a grid of plausible temperatures between cool (6000 K) and hot (10⁶ K) structures, the electron density is computed for representative effective thicknesses between 200 and 20,000 km. We obtain a relatively high maximum electron density, about 10¹³ cm⁻³. At such high electron densities, the Thomson continuum is negligible and therefore one would not expect a significant polarization degree in dense loops. We conclude that the Paschen and Brackett recombination continua are dominant in cool flare loops, while the free–free continuum emission is dominant for warmer and hot loops.

Motivated by the recent discovery of the binary neutron-star (BNS) merger GW170817, we determine the optimal observational setup for detecting and characterizing radio counterparts of nearby (d_L ∼ 40 Mpc) BNS mergers. We simulate GW170817-like radio transients, and radio afterglows generated by fast jets with isotropic energy ${E}_{\mathrm{iso}}\sim {10}^{50}$ erg, expanding in a low-density interstellar medium (ISM; ${n}_{\mathrm{ISM}}={10}^{-4}\mbox{--}{10}^{-2}$ cm⁻³), observed from different viewing angles (from slightly off-axis to largely off-axis). We then determine the optimal timing of GHz radio observations following the precise localization of the BNS radio counterpart candidate, assuming a sensitivity comparable to that of the Karl G. Jansky Very Large Array. The optimization is done so as to ensure that properties such as viewing angle and circumstellar density can be correctly reconstructed with the minimum number of observations. We show that radio is the optimal band to explore the fastest ejecta from BNSs in the low-density ISM, since the optical emission is likely to be dominated by the so-called "kilonova" component, while X-rays from the jet are detectable only for a small subset of the BNS models considered here. Finally, we discuss how future radio arrays like the next-generation VLA would improve the detectability of BNS mergers with physical parameters similar to those explored here.

We present an analysis of the caustic-crossing binary microlensing event OGLE-2017-BLG-0039. Thanks to the very long duration of the event, with a time scale t_E ∼ 130 days, the microlens parallax is measured precisely despite its low value of ${\pi }_{{\rm{E}}}\sim 0.06$. Analysis of the well-resolved caustic crossings during the source star's entrance and exit of the caustic yields an angular Einstein radius of ${\theta }_{{\rm{E}}}\sim 0.6$ mas. The measured ${\pi }_{{\rm{E}}}$ and ${\theta }_{{\rm{E}}}$ indicate that the lens is a binary composed of two stars with masses $\sim 1.0\,{M}_{\odot }$ and ∼0.15 M_⊙, and is located at a distance of ∼6 kpc. From the color and brightness of the lens estimated from its determined mass and distance, it is expected that ∼2/3 of the I-band blended flux comes from the lens. Therefore, the event is a rare case of a bright lens event for which high-resolution follow-up observations can confirm its nature.

The initial conditions of cosmological simulations are commonly drawn from a Gaussian ensemble. The limited number of modes inside simulations gives rise to sample variance: statistical fluctuations that limit the accuracy of the simulation predictions. Fixed fields offer an alternative initialization strategy; they have the same power spectrum as Gaussian fields but no intrinsic amplitude scatter. Paired fixed fields consist of two fixed fields with opposite phases that cancel phase correlations. We study the statistical properties of those fields for 19 different quantities at different redshifts through a large set of 600 N-body and 530 state-of-the-art magnetohydrodynamic simulations. We find that paired fixed simulations do not introduce a bias on any of the examined quantities. We quantify the statistical improvement brought by these simulations on different power spectra—matter, halos, cold dark matter, gas, stars, galaxies, and magnetic fields—finding that they can reduce their variance by factors as large as 10⁶. We quantify the improvement achieved by fixing and by pairing, showing that sample variance can be highly suppressed by pairing after fixing. Paired fixed simulations do not change the scatter in quantities such as the probability distribution function or the halo, void, or stellar mass functions. We argue that procedures aiming at reducing the sample variance of those quantities are unlikely to work. Our results show that paired fixed simulations do not affect either mean relations or scatter of galaxy properties and suggest that the information embedded in one-point statistics is highly complementary to that in clustering.

New infrared spectra are presented for H₂S and four other sulfur-containing compounds, all thiols, at 10–140 K to aid in the study of interstellar and solar system ices. Infrared spectral changes on warming H₂S and each thiol are described with an emphasis on the S–H stretching vibration at 2550–2525 cm⁻¹ (λ = 3.92–3.96 μm) as it is in a relatively unobscured part of the infrared spectra of interstellar and planetary ices. Infrared positions and band strengths for each thiol's S–H and C–H stretching vibrations are reported, along with the S–H band strength of H₂S. Two band strengths of near-infrared features of CH₃SH are included. Results for these compounds are compared, and some areas of agreement and disagreement with the literature are described.

A very long and nearly straight H i filament at about −60 km s⁻¹ in the southern Galactic hemisphere, seen nearly normal to the line of sight and well separated from low-velocity gas, has been studied in several ways in order to understand its physics, structure, and morphology. Gaussian analysis of 1800 profiles and examination of 140 declination–velocity cross sections shows that an underlying H i component, which is at least 15° long and about 1° wide, has a typical line width of 21 km s⁻¹. It does not appear to be in thermal pressure equilibrium with its surroundings; rather, it may be confined by a magnetic field of 18 μG. Narrow, elongated features (threads), probably unresolved in the 4' H i observations, have been identified within the boundaries of the filament. In general, each of these threads has two emission components, with line widths of the order of 8 and 3 km s⁻¹, which may wind around each other. Analysis suggests that these cooler components have an average density of 29 cm⁻³ and may be confined by a magnetic field of 5 μG. These results, taken together, can be explained if this southern filament has magnetic substructure.

We investigate the properties of the interstellar medium, star formation, and the current-day stellar population in the strongly lensed star-forming galaxy H-ATLAS J091043.1-000321 (SDP.11), at z = 1.7830, using new Herschel and Atacama Large Millimeter/submillimeter Array (ALMA) observations of far-infrared fine-structure lines of carbon, oxygen, and nitrogen. We report detections of the [O iii] 52 μm, [N iii] 57 μm, and [O i] 63 μm lines from Herschel/PACS, and present high-resolution imaging of the [C ii] 158 μm line, and underlying continuum, using ALMA. We resolve the [C ii] line emission into two spatially offset Einstein rings, tracing the red and blue velocity components of the line, in the ALMA/Band 9 observations at 02 resolution. The values seen in the [C ii]/far-infrared (FIR) ratio map, as low as ∼0.02% at the peak of the dust continuum, are similar to those of local ULIRGs, suggesting an intense starburst in this source. This is consistent with the high intrinsic FIR luminosity (∼3 × 10¹²L_⊙), ∼16 Myr gas depletion timescale, and ≲8 Myr timescale since the last starburst episode, estimated from the hardness of the UV radiation field. By applying gravitational lensing models to the visibilities in the uv-plane, we find that the lensing magnification factor varies by a factor of two across SDP.11, affecting the observed line profiles. After correcting for the effects of differential lensing, a symmetric line profile is recovered, suggesting that the starburst present here may not be the result of a major merger, as is the case for local ULIRGs, but instead could be powered by star formation activity spread across a 3–5 kpc rotating disk.

We present a new pulsar wind nebula (PWN) model that solves both advection and diffusion of nonthermal particles in a self-consistent way to satisfy the momentum and energy conservation laws. Assuming spherically symmetric (1D) steady outflow, we calculate the emission spectrum integrating over the entire nebula and the radial profile of the surface brightness. We find that the back reaction of the particle diffusion modifies the flow profile. The photon spectrum and the surface brightness profile are different from the model calculations without the back reaction of the particle diffusion. Our model is applied to the two well-studied PWNe, 3C 58 and G21.5-0.9. By fitting the spectra of these PWNe, we determine the parameter sets and calculate the radial profiles of X-ray surface brightness. For both the objects, obtained profiles of X-ray surface brightness and the photon index are well consistent with observations. Our model suggests that particles that have escaped from the nebula significantly contribute to the γ-ray flux. A γ-ray halo larger than the radio nebula is predicted in our model.

We analyze the metal accumulation in dwarf and spiral galaxies by following the history of metal enrichment and outflows in a suite of 20 high-resolution simulated galaxies. These simulations agree with the observed stellar and gas-phase mass–metallicity relation, an agreement that relies on large fractions of the produced metals escaping into the circumgalactic media. For instance, in galaxies with M_vir ∼ 10^9.5–10¹⁰${M}_{\odot }$, we find that about ∼85% of the available metals are outside of the galactic disk at z = 0, although the fraction decreases to a little less than half in Milky-Way-mass galaxies. In many cases, these metals are spread far beyond the virial radius. We analyze the metal deficit within the ISM and stars in the context of previous work tracking the inflow and outflow of baryons. Outflows are prevalent across the entire mass range, as is reaccretion. We find that between 40% and 80% of all metals removed from the galactic disk are later reaccreted. The outflows themselves are metal-enriched relative to the ISM by a factor of 0.2 dex because of the correspondence between sites of metal enrichment and outflows. As a result, the metal mass loading factor scales as ${\eta }_{\mathrm{metals}}\propto {v}_{\mathrm{circ}}^{-0.91}$, a somewhat shallower scaling than the total mass loading factor. We analyze the simulated galaxies within the context of analytic chemical evolution models by determining their net metal expulsion efficiencies, which encapsulate the rates of metal loss and reaccretion. We discuss these results in light of the inflow and outflow properties necessary for reproducing the mass–metallicity relation.

Instrumentation designed to characterize potentially habitable planets may combine adaptive optics and high-resolution spectroscopy techniques to achieve the highest possible sensitivity to spectral signs of life. Detecting the weak signal from a planet containing biomarkers will require exquisite control of the optical wavefront to maximize the planet signal and significantly reduce unwanted starlight. We present an optical technique, known as vortex fiber nulling (VFN), that allows polychromatic light from faint planets at extremely small separations from their host stars (≲λ/D) to be efficiently routed to a diffraction-limited spectrograph via a single-mode optical fiber, while light from the star is prevented from entering the spectrograph. VFN takes advantage of the spatial selectivity of a single-mode fiber to isolate the light from close-in companions in a small field of view around the star. We provide theoretical performance predictions of a conceptual design and show that VFN may be utilized to characterize planets detected by radial velocity (RV) instruments in the infrared without knowledge of the azimuthal orientation of their orbits. Using a spectral template-matching technique, we calculate an integration time of ∼400, ∼100, and ∼30 hr for Ross 128 b with Keck, the Thirty Meter Telescope, and the Large Ultraviolet/Optical/Infrared Surveyor, respectively.

The large-scale distribution of globular clusters in the central region of the Coma cluster of galaxies is derived through the analysis of Hubble Space Telescope/Advanced Camera for Surveys data. Data from three different HST observing programs are combined in order to obtain a full surface density map of globular clusters in the core of Coma. A total of 22,426 Globular cluster candidates were selected through a detailed morphological inspection and the analysis of their magnitude and colors in two wavebands, F475W (Sloan g) and F814W (I). The spatial distribution of globular clusters defines three main overdensities in Coma that can be associated with NGC 4889, NGC 4874, and IC 4051 but have spatial scales five to six times larger than individual galaxies. The highest surface density of globular clusters in Coma is spatially coincidental with NGC 4889. The most extended overdensity of globular clusters is associated with NGC 4874. Intracluster globular clusters also form clear bridges between Coma galaxies. Red globular clusters, which agglomerate around the center of the three main subgroups, reach higher surface densities than blue ones.

We explore effects of random nonaxisymmetric perturbations of kinetic helicity (the α effect) and diffusive decay of bipolar magnetic regions on generation and evolution of large-scale nonaxisymmetric magnetic fields on the Sun. Using a reduced 2D nonlinear mean-field dynamo model and assuming that bipolar regions emerge due to magnetic buoyancy in situ of the large-scale dynamo action, we show that fluctuations of the α effect can maintain the nonaxisymmetric magnetic fields through a solar-type α²Ω dynamo process. It is found that diffusive decay of bipolar active regions is likely to be the primary source of nonaxisymmetric magnetic fields observed on the Sun. Our results show that nonaxisymmetric dynamo models with stochastic perturbations of the α effect can explain periods of extremely high activity ("super-cycle" events) as well as periods of deep decline of magnetic activity. We compare the models with synoptic observations of solar magnetic fields for the last four activity cycles and discuss implications of our results for interpretation of observations of stellar magnetic activity.

Amorphous ice has long been invoked as a means for trapping extreme volatiles into solids, explaining the abundances of these species in comets and planetary atmospheres. Experiments have shown that this trapping is possible and has been used to estimate the abundances of each species in primitive ices after they have formed. However, these experiments have been carried out at deposition rates that exceed those expected in a molecular cloud or solar nebula by many orders of magnitude. Here, we develop a numerical model that reproduces the experimental results and apply it to those conditions expected in molecular clouds and protoplanetary disks. We find that two regimes of ice trapping exist: burial trapping, where the ratio of trapped species to water in the ice reflects that same ratio in the gas; and equilibrium trapping, where the ratio in the ice depends only on the partial pressure of the trapped species in the gas. The boundary between these two regimes is set by both the temperature and rate of ice deposition. These effects must be accounted for when determining the source of trapped volatiles during planet formation.

We here report a spectroscopic monitor for the supernova (SN) SN 2017iuk associated with the long-duration low-luminosity gamma-ray burst (GRB) GRB 171205A at a redshift of 0.037, which is up to now the third GRB–SN event away from us. Our spectroscopic observations and spectral analysis allow us to identify SN 2017iuk as a typical broad-line Type Ic SN. A comparison study suggests that the Type IcBL SN 2017iuk resembles SN 2006aj in the following aspects: (1) similar spectra at the nearby epochs, (2) comparable evolution of the photospheric velocity obtained from the measurements based on both the Si iiλ6355 line and spectral modeling, and (3) comparable explosion parameters. This analogy could imply the formation of a neutron star in the core collapse of GRB 171205A/SN 2017iuk as previously suggested in GRB 060218/SN 2006aj. The properties of the host galaxy are discussed, which suggest that GRB 171205A/SN 2017iuk occurred in an early-type (S0), high-mass, star-forming galaxy with low specific star formation rate and solar metallicity.

In order to relate the observed evolution of the galaxy stellar mass function and the luminosity function of active galactic nuclei (AGNs), we explore a coevolution scenario in which AGNs are associated only with the very last phases of the star-forming life of a galaxy. We derive analytically the connections between the parameters of the observed quasar luminosity functions and galaxy mass functions. The (m_bh/m_*)_Qing associated with quenching is given by the ratio of the global black hole accretion rate density (BHARD) and star formation rate density (SFRD) at the epoch in question. Observational data on the SFRD and BHARD suggest (m_bh/m_*)_Qing ∝ (1 + z)^1.5 below redshift 2. This evolution reproduces the observed mass–luminosity plane of Sloan Digital Sky Survey quasars, as well as the local m_bh/m_* relation in passive galaxies. The characteristic Eddington ratio, λ*, is derived from both the BHARD/SFRD ratio and the evolving L* of the AGN population. This increases up to z ∼ 2 as λ* ∝ (1 + z)^2.5, but at higher redshifts, λ* stabilizes at the physically interesting Eddington limit, λ* ∼ 1. The new model may be thought of as an opposite extreme to our earlier coevolution scenario in Caplar et al. The main observable difference between the two coevolution scenarios, presented here and in Caplar et al. is in the active fraction of low-mass star-forming galaxies. We compare the predictions with the data from deep multiwavelength surveys and find that the "quenching" scenario developed in the current paper is preferred.

We explore the gas morphology and excitation mechanisms of the ionization cones of the Type II Seyfert galaxy NGC 5728. Near-IR and optical data from the SINFONI and MUSE integral field units on the Very Large Telescope are combined with Hubble Space Telescope optical images, Chandra X-ray data, and Very Large Array radio observations. The complex nuclear structure has a star-forming (SF) ring with a diameter of 2 kpc. A radio jet impacts on the interstellar medium at about 200 pc from the nucleus, with the supernova remnants in the SF ring also present. Emission-line ratios of [Fe ii] and H ii show heavy extinction toward the nucleus, moderate extinction in the SF ring, and reduced extinction in the ionization cones. The active galactic nucleus (AGN) is hidden by a dust bar with up to 19 mag of visual extinction; the dust temperature at the nuclear position is ∼870 K. An X-ray jet is aligned with the ionization cones and associated with high-excitation emission lines of [Si vi] in a coronal line region extending 300 pc from the nucleus. Molecular hydrogen is spatially independent of the cones, concentrated in a disk equatorial to the SF ring, but also showing entrainment along the sides of the bicone. Gas masses for warm and cold H₂, H i, and H ii are estimated, and the excitation mechanisms for ionized and molecular gas are elucidated, from both optical (which shows a clean SF–AGN mixing sequence) and infrared diagnostics (which show more complicated, multicomponent excitation regimes).

We present a full data analysis of the pure-parallel Hubble Space Telescope (HST) imaging observations in the Brightest of Reionizing Galaxies Survey (BoRG[z9]) in Cycle 22. The medium-deep exposures with five HST/WFC3IR+UVIS filter bands from 79 independent sightlines (∼370 arcmin²) provide the least biased determination of number density for z ≳ 9 bright galaxies against cosmic variance. After a strict two-step selection for candidate galaxies, including dropout color and photometric redshift analyses, and revision of previous BoRG candidates, we identify one source at z ∼ 10 and two sources at z ∼ 9. The z ∼ 10 candidate shows evidence of line-of-sight lens magnification (μ ∼ 1.5), yet it appears surprisingly luminous (${M}_{\mathrm{UV}}\sim -22.6\pm 0.3$ mag), making it one of the brightest candidates at $z\gt 8$ known (∼0.3 mag brighter than the z = 8.68 galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z ∼ 9 candidates, we include previous data points at fainter magnitudes and find that the data are well fitted by a Schechter luminosity function with $\alpha =-{2.1}_{-0.3}^{+0.3}$, ${M}_{\mathrm{UV}}^{* }=-{21.0}_{-1.4}^{+0.7}$ mag, and $\mathrm{log}{\phi }^{* }=-{4.2}_{-0.9}^{+0.6}$ Mpc⁻³ mag⁻¹, for the first time without fixing any parameters. The inferred cosmic star formation rate density is consistent with unaccelerated evolution from lower redshift.

We present an analysis of the astrometric results from the Gaia second data release (DR2) for young stellar objects (YSOs) in star-forming regions related to the Gould Belt (GB). These regions are Barnard 59, Lupus 1 to 4, Chamaeleon I and II, Chamaeleontis, the Cepheus flare, IC 5146, and Corona Australis. The mean distance to the YSOs in each region is consistent with earlier estimations, though a significant improvement in the final errors was obtained. The mean distances to the star-forming regions were used to fit an ellipsoid of size (358 ± 7) ×(316 ± 13) × (70 ± 4) pc³, centered at (X₀, Y₀, Z₀) = (−82 ± 15, 39 ± 7, −25 ± 4) pc, consistent with recently determined parameters of the GB. The mean proper motions were combined with radial velocities from the literature to obtain the three-dimensional motions of the star-forming regions, which are consistent with a general expansion of the GB. We estimate that this expansion is occurring at a velocity of 2.5 ± 0.1 km s⁻¹. This is the first time that motions of YSOs have been used to investigate the kinematics of the GB. As an interesting side result, we also identified stars with large peculiar velocities.

A new model of the chemical evolution of primordial species in the Recombination Era, focusing on rovibrational molecular level populations and line emission, the main cooling process for low-temperature primordial gas, is presented. Since molecular excitation calculations are vital in determining particle velocity distributions, internal state distributions, abundances, and ionization balance in gaseous environments, our model of the early universe considers nonthermal level populations using new state-to-state collisional excitation rate coefficients and reaction rates. This model of Recombination Era astrochemistry highlights the level populations of ${{\rm{H}}}_{2}^{+}$, HD, and H₂ and expands upon the current chemical networks by considering deuterated, ionized, and excited species. We furthermore couple the heat equation to the chemical network to form a complete model of thermal balance and dynamical evolution of primordial gas in the early universe. A developmental version of the spectral synthesis package Cloudy was used to model the primordial gas, and a data set of ${{\rm{H}}}_{2}^{+}$ vibrational excitation rate coefficients due to H collisions are provided.

Bright high-redshift quasars (z > 6) hosting supermassive black holes (M_BH > 10⁸M_⊙) are expected to reside in massive host galaxies embedded within some of the earliest and most massive galaxy overdensities. We analyze 1.2 mm ALMA dust continuum maps of 35 bright quasars at 6 < z < 7 and search the primary beam for excess dust continuum emission from sources with L_IR ≳ 10¹²L_⊙ as evidence for early protoclusters. We compare the detection rates of continuum sources at ≥5σ significance in the fields surrounding the quasars (A_eff = 4.3 arcmin²) with millimeter number counts in blank field surveys. We discover 15 mm sources in the fields excluding the quasars themselves, corresponding to an overdensity of δ_gal ≡ (N_gal − N_exp)/N_exp = −0.07 ± 0.56, consistent with no detected overdensity of dusty galaxies within 140 physical kpc of the quasars. However, the apparent lack of continuum overdensity does not negate the hypothesis that quasars live in overdense environments, as evidenced by strong [C ii] overdensities found on the same scales as similarly selected quasars. The small field of view of ALMA could miss a true overdensity if it exists on scales larger than 1 cMpc, if the quasar is not centered in the overdensity, or if quasar feedback plays a role close to the quasar, but it is most likely that the large line-of-sight volume probed by a continuum survey will wash out a true overdensity signal. We discuss the necessary factors in determining the bias with which dusty star-forming galaxies trace true dark matter overdensities in order to improve upon overdensity searches in the dust continuum.

Heat flux suppression in collisionless plasmas for a large range of plasma β is explored using two-dimensional particle-in-cell simulations with a strong, sustained thermal gradient. We find that a transition takes place between whistler-dominated (high-β) and double-layer-dominated (low-β) heat flux suppression. Whistlers saturate at small amplitude in the low beta limit and are unable to effectively suppress the heat flux. Electrostatic double layers (DLs) suppress the heat flux to a mostly constant factor of the free-streaming value once this transition happens. The DL physics is an example of ion–electron coupling and occurs on a scale of roughly the electron Debye length. The scaling of ion heating associated with the various heat flux driven instabilities is explored over the full range of β explored. The range of plasma-βs studied in this work makes it relevant to the dynamics of a large variety of astrophysical plasmas, including the intracluster medium of galaxy clusters, hot accretion flows, stellar and accretion disk coronae, and the solar wind.

The Near Infrared Camera (NIRCam) on the James Webb Space Telescope (JWST) will be an incredibly powerful instrument for studying red supergiants (RSGs). The high luminosities and red peak wavelengths of these stars make them ideal targets for JWST/NIRCam. With effective photometric diagnostics in place, imaging RSG populations in multiple filters will make it possible to determine these stars' physical properties and, in cases where JWST pre-explosion imaging is available, to identify RSG supernova progenitors. This paper uses observed and model spectra of Galactic RSGs to simulate JWST/NIRCam near-IR photometry and colors, quantify and test potential diagnostics of effective temperature and bolometric magnitude, and present photometric techniques for separating background RSG and foreground dwarf populations. While results are presented for the full suite of near-IR filters, this work shows that (F070W–F200W) is the JWST/NIRCam color index most sensitive to effective temperature, F090W is the best band for determining bolometric magnitude, and the (F070W–F090W) versus (F090W–F200W) color–color diagram can be used to separate foreground dwarf and background RSG samples. The combination of these three filters is recommended as the best suite of photometric observations to use when studying RSGs with JWST.

The application of third moments to turbulence can determine the rate of the energy cascade. This approach is most readily done for statistically homogeneous turbulence in a uniform incompressible medium. Solar wind conditions near 1 au appear to fulfill these requirements sufficiently well to demonstrate that an energy cascade is active among interplanetary fluctuations with a rate sufficient for the inferred amount of proton heating. Fluctuation and solar-wind parameter ranges have been found where average cascade rates are calculated to have negative values that correspond to back-transfer of energy implying no proton heating. Additionally, individual outward and inward pseudo-energy cascade rates are anti-correlated rather than correlated, as they are for a power spectral cascade rate prediction. These negative rates and behaviors are shown here to be organized by inward pseudo-energy, which is generally the minor component of energy, and they occur below a threshold of inward pseudo-energy per unit mass of about 800 km² s⁻² for 12 hr intervals. Inward pseudo-energy is also shown to correlate with ambient solar-wind intervals that have decreasing wind speed and so correspond to rarefactions. These results imply that the average negative cascade rates may be the outcome of effects that are significant enough in these rarefactions to require a third-moment analysis that includes the effects of a nonuniform medium, principally flow gradients.

Depopulation of long-lived metastable helium He(2³S) by spontaneous radiative charge transfer in collisions with lithium cations Li⁺ is investigated using a fully quantal approach. The corresponding transitions start in continuum states of the initial electronic state b³Σ⁺ and end in continuum states of the final electronic state a³Σ⁺. The process is characterized by cross sections and rate coefficients, which are calculated as functions of initial collision energy and temperature, respectively. Particular consideration is paid to the proper description of the high-energy cross sections in order to include their contributions to the total rate coefficient at high temperatures, where its asymptotic behavior is analyzed. The calculated total rate coefficients are in the range 1.75 × 10⁻¹⁵ – 3.16 × 10⁻¹⁴ cm³ s⁻¹. The comparison with other relevant depopulation mechanisms shows that the radiative processes prevail for temperatures below 3000 K, while at higher temperatures the nonradiative inelastic processes are dominant.

A component of space weather, electron beams are routinely accelerated in the solar atmosphere and propagate through interplanetary space. Electron beams interact with Langmuir waves resulting in type III radio bursts. They expand along the trajectory and, using kinetic simulations, we explore the expansion as the electrons propagate away from the Sun. Specifically, we investigate the front, peak, and back of the electron beam in space from derived radio brightness temperatures of fundamental type III emission. The front of the electron beam travels at speeds from 0.2c to 0.7c, significantly faster than the back of the beam, which travels at speeds between 0.12c and 0.35c. The difference in speed between the front and the back elongates the electron beam in time. The rate of beam elongation has a 0.98 correlation coefficient with the peak velocity, in line with predictions from type III observations. The inferred speeds of electron beams initially increase close to the acceleration region and then decrease through the solar corona. Larger starting densities and harder initial spectral indices result in longer and faster type III sources. Faster electron beams have higher beam energy densities, and produce type IIIs with higher peak brightness temperatures and shorter FWHM durations. Higher background plasma temperatures also increase speed, particularly at the back of the beam. We show how our predictions of electron beam evolution influences type III bandwidth and drift rates. Our radial predictions of electron beam speed and expansion can be tested by the upcoming in situ electron beam measurements made by Solar Orbiter and Parker Solar Probe.

Using observations by the Solar Dynamics Observatory from 2010 June to 2017 December, we have performed the first statistical investigation of circular-ribbon flares (CFs) and examined the white-light emission in them. We find 90 CFs occurring in 36 active regions (ARs), including eight X-class, 34 M-class, and 48 C- and B-class flares. The occurrence rate of white-light flares (WLFs) is 100% (8/8) for X-class CFs, ∼62% (21/34) for M-class CFs, and ∼8% (4/48) for C- and B-class CFs. Sometimes we observe several CFs in a single AR, and nearly all of them are WLFs. Compared to normal CFs, those with white-light enhancement tend to have a shorter duration, smaller size, stronger electric current and more complicated magnetic field. We find that for X-class WLFs, the white-light enhancement is positively correlated with the flare class, implying that it is largely determined by the amount of released energy. However, there is no such correlation for M- and C-class WLFs, suggesting that other factors such as the timescale, spatial scale, and magnetic field complexity may play important roles in the generation of white-light emission if the released energy is not high enough.

As part of our work on nitrogen-rich ices, the IR spectra and band strengths used in a recent paper to identify and quantify radiation-induced changes in an N₂+H₂O ice near 15 K are examined, along with reports of (i) a chemical tracer for N₂+H₂O ices, (ii) a new IR feature of solid N₂, and (iii) a striking ¹⁵N isotopic enrichment. Problems are found for each IR band strength used and for each of the three claims made, to the extent that none are supported by the results presented to date. In contrast, new work presented here, combined with several older investigations, strongly supports the formation of di- and triatomic nitrogen oxides in irradiated N₂-rich ices. Observations and trends in the chemistry of N₂-rich icy solids are described, and conclusions are drawn. A considerable amount of material from previous chemical studies of N₂-rich systems, spanning more than a century, is brought together for the first time and used to examine the chemistry of N₂-rich ices in extraterrestrial environments. Needs are identified and suggestions made for future studies of N₂-rich interstellar and planetary ice analogs.

In the first paper of this series, we presented our upgraded cool white dwarf atmosphere code. In this second paper, we use our new models to analyze SDSS J080440.63+223948.6 (J0804+2239), the first DZ star to show collision-induced absorption (CIA). This object provides a crucial test for our models, since previous versions of our code were unable to simultaneously fit the metal absorption lines and the CIA. We find an excellent fit to both the spectroscopic and photometric data, which further validates the improved constitutive physics of our models. We also show that the presence of metal lines allows lift of the degeneracy between high and low hydrogen abundances that usually affects the fits of white dwarfs with CIA. Finally, we investigate the potential impact of spectroscopically undetected metals on the photometric solutions of DC stars.

We report on the results of active galactic nuclei (AGNs) detection by NuSTAR performed in three extragalactic survey fields (COSMic Evolutionary Survey field (COSMOS), Ultra Deep Survey (UDS), and Extended Chandra Deep Field-South (ECDFS)) in three hard bands, namely H1 (8–16 keV), H2 (16–24 keV), and VH (35–55 keV). The aggregated area of the surveys is ∼2.7 deg². While a large number of sources is detected in the H1 band (72 at the 97% level of reliability), the H2 band directly probing close to the peak of the Cosmic X-ray Background (CXB) returns four significant detections, and two tentative (although not significant) detections are found in the VH-band. All of the sources detected above 16 keV are also detected at lower energies. We compute the integral number counts for sources in such bands, which show broad consistency with population-synthesis models of the CXB. We furthermore identify two Compton-thick AGNs, one in the COSMOS field, associated with a hard and faint Chandra source, and one in the UDS field, never detected in the X-ray band before. Both sources are at the same redshift z ∼ 1.25, which shifts their Compton-hump into the H1 band, and were previously missed in the usually employed NuSTAR bands, confirming the potential for using the H1 band to discover obscured AGNs at z > 1 in deep surveys.

The shape of the radial distribution of blue straggler stars (BSS), when normalized to a reference population of horizontal branch (HB) stars, has been found to be a powerful indicator of the dynamical evolution reached by a globular cluster (GC). In particular, observations suggest that the BSS distribution bimodality is modulated by the dynamical age of the host GC; dynamically unrelaxed GCs show a flat BSS distribution, and more relaxed GCs show a minimum at a radius that increases for increasing dynamical age, resulting in a natural "dynamical clock." While direct N-body simulations are able to reproduce the general trend, thus supporting its dynamical origin, the migration of the minimum of the distribution appears to be noisy and not well defined. Here we show that a simple unidimensional model based on dynamical friction (drift) and Brownian motion (diffusion) correctly reproduces the qualitative motion of the minimum, without adjustable parameters except for the BSS to HB stars mass ratio. Differential dynamical friction effects combine with diffusion to create a bimodality in the BSS distribution and to determine its evolution, driving the migration of the minimum to larger radii over time. The diffusion coefficient is strongly constrained by the need to reproduce the migratory behavior of the minimum, and the radial dependence of diffusion set by fundamental physical arguments automatically satisfies this constraint. Therefore, our model appears to capture the fluctuation–dissipation dynamics that underpins the dynamical clock.

Thanks to the Cassini–Huygens mission, it is now established that the first aerosols in Titan's upper atmosphere are found from an altitude of ∼1200 km. Once they are formed and through their descent toward the surface, these nanoparticles are submitted to persistent far-ultraviolet (FUV) radiation that can reach lower atmospheric layers. Such an interaction has an impact, especially on the chemistry and charge budget of the atmospheric compounds. Models are useful to understand this photoprocessing, but they lack important input data such as the photoemission threshold or the absolute photoabsorption/emission cross sections of the aerosols. In order to quantify the photoemission processes, analogs of Titan's aerosols have been studied with the DESIRS FUV beamline at the synchrotron SOLEIL as isolated substrate-free nanoparticles. We present here the corresponding angle-resolved photoelectron spectroscopy data recorded at different FUV photon energies. The results show a very low photoionization threshold (6.0 ± 0.1 eV ∼ 207 nm) and very high absolute ionization cross sections (∼10⁶ Mb), indicating that FUV photoemission from aerosols is an intense source of slow electrons that has to be taken into account in photochemical models of Titan's atmosphere.

We present Atacama Large Millimeter/Submillimeter Array CO(3–2) observations at 03 resolution of He 2–10, a starburst dwarf galaxy and possible high-z galaxy analog. The warm dense gas traced by CO(3–2) is found in clumpy filaments that are kinematically and spatially distinct. The filaments have no preferred orientation or direction; this may indicate that the galaxy is not evolving into a disk galaxy. Filaments appear to be feeding the active starburst; the velocity field in one filament suggests acceleration onto an embedded star cluster. The relative strengths of CO(3–2) and radio continuum vary strongly on decaparsec scales in the starburst. There is no CO(3–2) clump coincident with the nonthermal radio source that has been suggested to be an AGN, nor unusual kinematics. The kinematics of the molecular gas show significant activity that is apparently unrelated to the current starburst. The longest filament, east of the starburst, has a pronounced shear of FWHM ∼40 km s⁻¹ across its ∼50 pc width over its entire ≈0.5 kpc length. The cause of the shear is not clear. This filament is close in projection to a "dynamically distinct" CO feature previously seen in CO(1–0). The most complex region and the most highly disturbed gas velocities are in a region 200 pc south of the starburst. The CO(3–2) emission there reveals a molecular outflow, of line width FWZI ∼ 120–140 km s⁻¹, requiring an energy ≳10⁵³ erg s⁻¹. There is at present no candidate for the driving source of this outflow.

We observed five giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) in the ¹²CO J = 1–0 line using the Atacama Large Millimeter/submillimeter Array (ALMA). The sample includes four GMCs with some signs of star formation—either YSOs, H ii regions, and/or young clusters—and one quiescent GMC without any sign of massive star formation. The data from the ALMA 12 m, 7 m, and Total-Power arrays are jointly deconvolved to obtain high-fidelity images at high spatial resolution (3'' = 0.7 pc). The four star-forming GMCs show very complex structures with clumps and filaments. The quiescent GMC shows a relatively diffuse, extended emission distribution without prominent clumps or filaments. This difference is similar to that between structured molecular gas in Milky Way spiral arms and unstructured gas in the inter-arm regions. We characterize the difference with the brightness distribution function and brightness distribution index. In conjunction with other ALMA studies of GMCs in the LMC, the five GMCs tentatively form an evolutionary trend: from less structured, quiescent GMCs to more structured, actively star-forming GMCs. A future ALMA study will be able to map molecular clouds over the LMC and reveal the evolutionary sequence of molecular clouds.

An unbiased search of molecular outflows within the region of the CO High Resolution survey has identified 157 high-mass outflows from a sample of 770 APEX Telescope Large Area Survey of the Galaxy clumps with a detection rate of 20%. The detection rate of outflows increases for clumps with higher M_clump, L_bol, L_bol/M_clump, ${N}_{{{\rm{H}}}_{2}}$, and T_dust compared to the clumps with no outflow. The detection rates of the outflow increase from protostellar (8%) to young stellar object clump (17%) to massive star-forming clump (29%). The detection rate 26% for quiescent clump is preliminary, because the sample of quiescent clumps is small. A statistical relation between the outflow and clump masses for our sample is $\mathrm{log}({M}_{\mathrm{out}}/{M}_{\odot })=(-1.1\pm 0.21)$$+\,(0.9\pm 0.07)\mathrm{log}({M}_{\mathrm{clump}}/{M}_{\odot })$. The detection rate of outflows and the outflow mass-loss rate show an increase with increasing M_clump, L_bol, ${N}_{{{\rm{H}}}_{2}}$, and T_dust, which indicates that clumps with outflow with higher parameter values are at a more advanced evolutionary stage. The outflow mechanical force increases with increasing bolometric luminosities. No clear evidence has yet been found that higher-mass outflows have different launching conditions than low-mass outflows.