Table of contents

We present models of the Hβ-emitting broad-line region (BLR) in seven Seyfert 1 galaxies from the Lick AGN Monitoring Project 2011 sample, drawing inferences on the BLR structure and dynamics as well as the mass of the central supermassive black hole. We find that the BLR is generally a thick disk, viewed close to face-on, with preferential emission back toward the ionizing source. The dynamics in our sample range from near-circular elliptical orbits to inflowing or outflowing trajectories. We measure black hole masses of ${\mathrm{log}}_{10}({M}_{\mathrm{BH}}/{M}_{\odot })={6.48}_{-0.18}^{+0.21}$ for PG 1310−108, ${7.50}_{-0.18}^{+0.25}$ for Mrk 50, ${7.46}_{-0.21}^{+0.15}$ for Mrk 141, ${7.58}_{-0.08}^{+0.08}$ for Mrk 279, ${7.11}_{-0.17}^{+0.20}$ for Mrk 1511, ${6.65}_{-0.15}^{+0.27}$ for NGC 4593, and ${6.94}_{-0.14}^{+0.14}$ for Zw 229−015. We use these black hole mass measurements along with cross-correlation time lags and line widths to recover the scale factor f used in traditional reverberation mapping measurements. Combining our results with other studies that use this modeling technique, which brings our sample size to 16, we calculate a scale factor that can be used for measuring black hole masses in other reverberation mapping campaigns. When using the root-mean-square (rms) spectrum and using the line dispersion to measure the line width, we find ${\mathrm{log}}_{10}({f}_{\mathrm{rms},\sigma })$_pred = 0.57 ± 0.19. Finally, we search for correlations between f and other AGN and BLR parameters and find marginal evidence that f is correlated with M_BH and the BLR inclination angle, but no significant evidence of a correlation with the AGN luminosity or Eddington ratio.

We conduct a multiwavelength morphological study of the Galactic supernova remnant (SNR) RX J0852.0–4622 (also known as Vela Jr., Vela Z, and G266.2−1.2). RX J0852.0–4622 is coincident with the edge of the larger Vela SNR causing confusion in the attribution of some filamentary structures to either RX J0852.0–4622 or its larger sibling. We find that the RX J0852.0–4622 radio-continuum emission can be characterized by a two-dimensional shell with a radius of 090 ± 001 (or 11.8 ± 0.6 pc at an assumed distance of 750 pc) centered at (l, b) = (13308 ± 001,−4634 ± 001) (or R.A. = 8^h52^m192, decl. = −46°20'240, J2000), consistent with X-ray and gamma-ray emission. Although [O iii] emission features are generally associated with the Vela SNR, one particular [O iii] emission feature, which we denote as "the Vela Claw," morphologically matches a molecular clump that is thought to have been stripped by the stellar progenitor of the RX J0852.0–4622 SNR. We argue that the Vela Claw feature is possibly associated with RX J0852.0–4622. Toward the northwestern edge of RX J0852.0–4622 , we find a flattening of the radio spectral index toward another molecular clump also thought to be associated with RX J0852.0–4622 . It is currently unclear whether this feature and the Vela Claw result from interactions between the RX J0852.0–4622 shock and interstellar medium gas.

Mergers of galaxies are an important mode for galaxy evolution because they serve as an efficient trigger of powerful starbursts. However, observational studies of molecular gas properties during their early stages are scarce. We present interferometric CO(2–1) maps of two luminous infrared galaxies, NGC 3110 and NGC 232, obtained with the Submillimeter Array with ∼1 kpc resolution. While NGC 3110 is a spiral galaxy interacting with a minor (14:1 stellar mass) companion, NGC 232 is interacting with a similarly sized object. We find that such interactions in these galaxies have likely induced enhancements in the molecular gas content and central concentrations, partly at the expense of atomic gas. The obtained molecular gas surface densities in their circumnuclear regions are Σ_mol ≳ 10^2.5M_⊙ pc⁻², higher than in noninteracting objects by an order of magnitude. Gas depletion times of  0.5–1 Gyr are found for the different regions, lying in between noninteracting disk galaxies and the starburst sequence. In the case of NGC 3110, the spiral arms show on average 0.5 dex shorter depletion times than in the circumnuclear regions if we assume a similar H₂–CO conversion factor. We show that even in the early stages of the interaction with a minor companion, a starburst is formed along the circumnuclear region and spiral arms, where a large population of SSCs is found (∼350), and at the same time a large central gas concentration is building up that might be the fuel for an active galactic nucleus. The main morphological properties of the NGC 3110 system are reproduced by our numerical simulations and allow us to estimate that the current epoch of the interaction is at ∼150 Myr after closest approach.

To understand the galaxy population in clusters today, we should also consider the impact of previous environments prior to cluster infall, namely preprocessing. We use the Yonsei Zoom-in Cluster Simulation, a hydrodynamic high-resolution zoom-in simulation of 15 clusters, and focus on the tidal stripping suffered by the dark matter halos of cluster members due to preprocessing. We find that ∼48% of today's cluster members were once satellites of other hosts. This is slightly higher than previous estimates, in part because we consider not just group-mass hosts but hosts of all masses. Thus, we find that the preprocessed fraction is poorly correlated with cluster mass and is instead related to each cluster's recent mass growth rate. Hosts less massive than groups are significant contributors, providing more than one-third of the total preprocessed fraction. We find that halo mass loss is a clear function of the time spent in hosts. However, two factors can increase the mass-loss rate considerably: the mass ratio of a satellite to its host and the cosmological epoch when the satellite was hosted. The latter means we may have previously underestimated the role of high-redshift groups. From a sample of heavily tidally stripped members in clusters today, nearly three-quarters were previously in a host. Thus, visibly disturbed cluster members are more likely to have experienced preprocessing. Being hosted before cluster infall enables cluster members to experience tidal stripping for extended durations compared to direct cluster infall and at earlier epochs when hosts were more destructive.

We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 404 at 1.25 μm (J band) and 2.2 μm (K band) near-infrared (NIR) wavelengths. Although NGC 404 is thought to host an intermediate-mass black hole (BH) at its center, it has been unclear whether accretion onto the BH or another mechanism such as shock excitation drives its LINER emission at optical/NIR wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of [Fe ii], H₂, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H₂ gas is in a central rotating disk, and ratios of multiple H₂ lines indicate that the molecular gas is thermally excited, with some contribution from UV fluorescence. The [Fe ii] emission is more extended and diffuse than the molecular gas and has a different kinematic structure that reaches higher velocities/dispersions. We also map the strength of the CO stellar absorption feature and constrain the dominant age of the nuclear stellar population to ∼1 Gyr. Finally, we find regions across the nucleus of NGC 404 with [Fe ii]/Paβ line ratios up to 6.5, ∼2.5 times higher than the ratio measured from spatially integrated spectra. From these high line ratios, we conclude that shocks are the dominant physical mechanism exciting NGC 404's LINER emission and argue that a possible source of this shock excitation is a supernova remnant.

HD 81809 has one of the highest quality activity cycles from the sample of stars synoptically observed in the Mount Wilson Observatory HK Project. However, this object is in fact a binary system, raising the question as to which of the components is responsible for the observed cyclic activity and what are the properties of that active component. The Hipparcos spacecraft obtained resolved two-color photometry for this system that indicates that both components are near the solar temperature. Combined with the precise Gaia parallax and empirical bolometric corrections we derive component the luminosities of ${L}_{{\rm{A}}}=5.8\pm 0.3\,{{ \mathcal L }}_{\odot }^{{\rm{N}}}$ and ${L}_{{\rm{B}}}=1.025\pm 0.055\,{{ \mathcal L }}_{\odot }^{{\rm{N}}}$, and radii ${R}_{{\rm{A}}}=2.42\pm 0.08\,{{ \mathcal R }}_{\odot }^{{\rm{N}}}$ and ${R}_{{\rm{B}}}=1.04\pm 0.04\,{{ \mathcal R }}_{\odot }^{{\rm{N}}}$, confirming that the primary component is a subgiant. We perform an independent estimate of the rotation period of the A component based on $v\sin i$ and find that it agrees with the 40.2 days period previously measured from the Ca HK time series. We explore plausible scenarios for the deconvolved S-index and find that a cycling A component would have an activity level within the bounds of ensemble activity-rotation trends, while a cycling B component likely does not. Based on the available rotation and activity evidence, we find the most likely characterization of the system is a subgiant primary component responsible for the smooth cyclic behavior in Ca HK with $\mathrm{log}({R}_{\mathrm{HK}}^{{\prime} })\sim -4.89$, while the secondary component has relatively flat activity at $\mathrm{log}({R}_{\mathrm{HK}}^{{\prime} })\sim -5.02$.

Studies of solar wind turbulence traditionally employ high-resolution magnetic field data, but high-resolution measurements of ion and electron moments have been possible only recently. We report the first turbulence studies of ion and electron velocity moments accumulated in pristine solar wind by the Fast Plasma Investigation (FPI) instrument on board the Magnetospheric Multiscale Mission. Use of these data is made possible by a novel implementation of a frequency domain Hampel filter, described herein. After presenting procedures for processing of the data, we discuss statistical properties of solar wind turbulence extending into the kinetic range. Magnetic field fluctuations dominate electron and ion-velocity fluctuation spectra throughout the energy-containing and inertial ranges. However, a multispacecraft analysis indicates that at scales shorter than the ion inertial length, electron velocity fluctuations become larger than ion-velocity and magnetic field fluctuations. The kurtosis of ion-velocity peaks around a few ion inertial lengths and returns to a near Gaussian value at sub-ion scales.

We have observed a glitch in the Crab pulsar (PSR B0531+21) in the 0.5–10 keV X-ray band with the X-Ray Pulsar Navigation-I (XPNAV-1) satellite. This glitch occurred around 2017 November 8. Observations at radio frequency by the Jodrell Bank observatory and the Lovell telescope have confirmed it to be the largest ever observed. We report the results of X-ray observation of this glitch. The measured rotation frequency increase of the Crab is Δν₀ = (14.3 ± 2.0) × 10⁻⁶ Hz, corresponding to a fractional increase of Δν₀/ν₀ = (0.48 ± 0.09) × 10⁻⁶. Two transient components in the rotation frequency change are detected: one is the short transient term of Δν_n1 = 6.6 × 10⁻⁶ Hz with a timescale of 38.6 days and the other is the very short one of Δν_n2 = −1.35 × 10⁻⁶ Hz with a timescale of 2.4 days. The step change in the rotation frequency derivative is determined to be ${\rm{\Delta }}{\dot{\nu }}_{0}=(3.6\pm 1.9)\times {10}^{-12}$ Hz s⁻¹. We also examine the relationship between the persistent offset ${\rm{\Delta }}{\dot{\nu }}_{{\rm{p}}}$ and Δν₀, giving ${\rm{\Delta }}{\dot{\nu }}_{{\rm{p}}}=7\times {10}^{-8}\times {\rm{\Delta }}{\nu }_{0}$. No significant X-ray flux changes are observed pre- and post-glitch.

The Fermi γ-ray source 1FGL J1417.7–4407 (J1417) is a compact X-ray binary with a neutron star primary and a red giant companion in a ∼5.4 days orbit. This initial conclusion, based on optical and X-ray data, was confirmed when a 2.66 ms radio pulsar was found at the same location (and with the same orbital properties) as the optical/X-ray source. However, these initial studies found conflicting evidence about the accretion state and other properties of the binary. We present new optical, radio, and X-ray observations of J1417 that allow us to better understand this unusual system. We show that one of the main pieces of evidence previously put forward for an accretion disk—the complex morphology of the persistent Hα emission line—can be better explained by the presence of a strong, magnetically driven stellar wind from the secondary and its interaction with the pulsar wind. The radio spectral index derived from VLA/ATCA observations is broadly consistent with that expected from a millisecond pulsar, further disfavoring an accretion disk scenario. X-ray observations show evidence for a double-peaked orbital light curve, similar to that observed in some redback millisecond pulsar binaries and likely due to an intrabinary shock. Refined optical light-curve fitting gives a distance of 3.1 ± 0.6 kpc, confirmed by a Gaia DR2 parallax measurement. At this distance the X-ray luminosity of J1417 is (${1.0}_{-0.3}^{+0.4}$) ×10³³ erg s⁻¹, which is more luminous than all known redback systems in the rotational-powered pulsar state, perhaps due to the wind from the giant companion. The unusual phenomenology of this system and its differing evolutionary path from redback millisecond pulsar binaries points to a new eclipsing pulsar "spider" subclass that is a possible progenitor of normal field millisecond pulsar binaries.

Progress in understanding of giant planet formation has been hampered by a lack of observational constraints to growing protoplanets. Recently, detection of an Hα-emission excess via direct imaging was reported for the protoplanet LkCa15b orbiting the pre-main-sequence star LkCa15. However, the physical mechanism for the Hα emission is poorly understood. According to recent high-resolution three-dimensional hydrodynamic simulations of the flow accreting onto protoplanets, the disk gas flows down almost vertically onto and collides with the surface of a circumplanetary disk at a supersonic velocity and thus passes through a strong shockwave. The shock-heated gas is hot enough to generate Hα emission. Here we develop a one-dimensional radiative hydrodynamic model of the flow after the shock by detailed calculations of chemical reactions and electron transitions in hydrogen atoms, and quantify the hydrogen line emission in the Lyman-, Balmer-, and Paschen-series from the accreting gas giant system. We then demonstrate that the Hα intensity is strong enough to be detected with current observational techniques. Comparing our theoretical Hα intensity with the observed one from LkCa15b, we constrain the protoplanet mass and the disk gas density. Observation of hydrogen line emission from protoplanets is highly encouraged to obtain direct constraints of accreting gas giants, which will be key in understanding the formation of gas giants.

To help identify interplanetary coronal mass ejections (ICMEs) in New Horizons (NH) Solar Wind Around Pluto observations, we developed a method for determining the alpha to proton density ratio (n_α/n_p). Many common ICME signatures are derived from plasma and field parameters with values inside transient ICMEs distinct from values in the background solar wind. As the solar wind propagates, the plasma parameters evolve with increasing heliocentric distance, and ICMEs interact with the background solar wind. Some ICME signatures are based on composition such as the alpha (He⁺⁺) to proton (H⁺) number density ratio, which is frequently enhanced in ICMEs. Intervals with enhanced n_α/n_p ratios persist into the outer heliosphere even though individual solar wind parameters evolve as solar wind propagates farther from the Sun. Overall, the solar wind expands as it propagates, but parcels of differing speeds dynamically interact, forming compressions and rarefactions, and altering the solar wind parameters. Both n_α and n_p change in lock step during such dynamic interactions, keeping the n_α/n_p ratio fixed. Our n_α/n_p results are consistent with prior missions, and we find that enhanced levels of n_α/n_p often occur within intervals of low proton temperature, which is the only other reliable ICME signature that NH can measure. Eventually, enhanced n_α/n_p values will likely become the most reliable ICME indicator for NH if the ICME temperatures become indistinguishable from background levels. NH is heading toward the Energetic Neutral Atom ribbon, and should have enough power to reach the termination shock.

In this work, we studied MHD modes in a magnetically twisted flux tube with a twisted flow that is embedded in the uniform magnetic field. We consider when the azimuthal magnetic field and velocity are linear functions of radius (case i) and also more generally when they are arbitrary functions of radius (case ii). Under these assumptions, we obtain the dispersion equation in the incompressible limit. This solution can also be used to describe the MHD perturbations in plasma pinches and vortices. The dispersion equation is simplified by implementing the thin flux tube approximation. It is shown that sausage modes (m = 0) become unstable for large enough azimuthal flow speeds. Also, we obtained the unstable modes for m > 0. It is shown that the stability criterion of the m = 1 mode (for case i) is independent of the background azimuthal components of the plasma velocity and magnetic field. These criteria fully coincide with the result that was previously obtained by Syrovatskiy for a plane interface. Moreover, this result even remains valid when the azimuthal magnetic field and velocity have an arbitrary dependence on radius (case ii). A criterion for the stability of the m ≥ 2 modes is also obtained. It was found that instability of these modes is determined by both longitudinal and azimuthal flows. It is shown that if there is sufficient azimuthal background flow, then all modes with m ≥ 2 will become unstable.

We compare multi-epoch sub-arcsecond Very Large Array imaging of the 22 GHz water masers toward the massive protocluster NGC 6334I observed before and after the recent outburst of MM1B in (sub)millimeter continuum. Since the outburst, the water maser emission toward MM1 has substantially weakened. Simultaneously, the strong water masers associated with the synchrotron continuum point source CM2 have flared by a mean factor of 6.5 (to 4.2 kJy) with highly blueshifted features (up to 70 km s⁻¹ from the LSR) becoming more prominent. The strongest flaring water masers reside 3000 au north of MM1B and form a remarkable bow shock pattern whose vertex coincides with CM2 and tail points back to MM1B. Excited OH masers trace a secondary bow shock located ∼120 au downstream. Atacama Large Millimeter Array images of CS (6–5) reveal a highly collimated north–south structure encompassing the flaring masers to the north and the nonflaring masers to the south seen in projection toward the MM3-UCHII region. Proper motions of the southern water masers over 5.3 years indicate a bulk projected motion of 117 km s⁻¹ southward from MM1B with a dynamical time of 170 years. We conclude that CM2, the water masers, and many of the excited OH masers trace the interaction of the high-velocity bipolar outflow from MM1B with ambient molecular gas. The previously excavated outflow cavity has apparently allowed the radiative energy of the current outburst to propagate freely until terminating at the northern bow shock where it strengthened the masers. Additionally, water masers have been detected toward MM7 for the first time, and a highly collimated CS (6–5) outflow has been detected toward MM4.

More than 20 precataclysmic variable (pre-CV) systems have now been discovered with very short orbital periods ranging from 250 minutes down to 68 minutes. A pre-CV consists of a white dwarf (WD) or hot subdwarf primary and a low-mass companion star, where the companion star has successfully ejected the common envelope (CE) of the primary progenitor, but mass transfer from the companion star to the primary has not yet commenced. In this short-period range, a substantial fraction of the companion stars are likely to be either brown dwarfs with masses ≲0.07 M_⊙ or stars at the bottom of the main sequence (MS; ≲0.1 M_⊙). The discovery of these short-period pre-CVs raises the question, what is the shortest possible orbital period of such systems? We ran 500 brown dwarf/low-mass MS models with Modules for Experiments in Stellar Astrophysics that cover the mass range from 0.002 to 0.1 M_⊙. We find that the shortest possible orbital period is 40 minutes, with a corresponding brown dwarf mass of 0.07 M_⊙ for an age equal to a Hubble time. We discuss the past evolution of these systems through the CE and suggest that many of the systems with present-day WD primaries may have exited the CE with the primary as a helium-burning hot subdwarf. We also characterize the future evolution of the observed systems, which includes a phase as CVs below the conventional period minimum.

The weak field approximation (WFA) is a conceptually simple and computationally light method for inferring the magnetic field strength and its orientation in the Sun's atmosphere. In this work, we study the validity and limitations of this tool when applied to full Stokes Ca ii 8542 Å profiles to extract information about the chromospheric magnetic field. We find that the range of validity of the WFA depends, among other things, on the component of the magnetic field that one is trying to infer. The retrieval of the line-of-sight component of the chromospheric magnetic field from the core of the spectral line is reliable for field strengths up to ∼1200 G, even when moderate velocity gradients are present. The horizontal component, on the other hand, is suitably derived using the wing–core boundary of the spectral line, but typically yields systematic errors of $\geqslant 10 \%$. The effects of scattering polarization further compound the problem by rendering the transverse field inference problematic in quiet Sun areas, and for observing geometries within 30^◦ of the limb. Magneto-optical effects disproportionately challenge the determination of the magnetic field azimuth in the transverse plane, leading to errors of $\sim 10^\circ$. Typical noise levels of ${\sigma }_{{\rm{n}}}={10}^{-3}$ relative to the continuum intensity preclude the accurate retrieval of the transverse field strength and its azimuth below a threshold of a few hundred Gauss. Striving for a noise level of ${\sigma }_{{\rm{n}}}={10}^{-4}$ significantly improves the diagnostic capability of the WFA with this spectral line, at which point the magnetic field inference becomes limited by systematic errors.

We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ∼2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 deg² area with ∼10' resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map, yielding a best-fit inclination angle $i={25.86}_{-1.39}^{+0.73}$ degrees with random errors of ±019 and line-of-nodes position angle $\theta ={149.23}_{-8.35}^{+6.43}$ degrees with random errors of ±049. These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at ρ ∼ 7° that departs from the defined LMC plane up to ∼4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5°–15° relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.

We use cosmological hydrodynamical simulations to investigate the role of feedback from accreting black holes in the evolution of the size, compactness, stellar core density, and specific star formation of massive galaxies with stellar masses of ${M}_{* }\gt {10}^{10.9}\,{M}_{\odot }$. We perform two sets of cosmological zoom-in simulations of 30 halos to z = 0: (1) without black holes and active galactic nucleus (AGN) feedback and (2) with AGN feedback arising from winds and X-ray radiation. We find that AGN feedback can alter the stellar density distribution, reduce the core density within the central 1 kpc by 0.3 dex from z = 1, and enhance the size growth of massive galaxies. We also find that galaxies simulated with AGN feedback evolve along tracks similar to those characterized by observations of specific star formation rate versus compactness. We confirm that AGN feedback plays an important role in transforming galaxies from blue compact galaxies into red extended galaxies in two ways: (1) it effectively quenches the star formation, transforming blue compact galaxies into compact quiescent galaxies, and (2) it also removes and prevents new accretion of cold gas, shutting down in situ star formation and causing subsequent mergers to be gas-poor or mixed. Gas-poor minor mergers then build up an extended stellar envelope. AGN feedback also puffs up the central region through fast AGN-driven winds as well as the slow expulsion of gas while the black hole is quiescent. Without AGN feedback, large amounts of gas accumulate in the central region, triggering star formation and leading to overly massive blue galaxies with dense stellar cores.

Despite the hypothesized similar face-on viewing angles, the infrared emission of type-1 active galactic nuclei (AGNs) has diverse spectral energy distribution (SED) shapes that deviate substantially from the well-characterized quasar templates. Motivated by the commonly seen UV-optical obscuration and the discovery of parsec-scale mid-IR polar dust emission in some nearby AGNs, we develop semi-empirical SED libraries for reddened type-1 AGNs built on quasar intrinsic templates, assuming low-level extinction caused by an extended distribution of large dust grains. We demonstrate that this model can reproduce the nuclear UV to IR SED and the strong mid-IR polar dust emission of NGC 3783, the type-1 AGN with the most relevant and robust observational constraints. In addition, we compile 64 low-z Seyfert-1 nuclei with negligible mid-IR star formation contamination and satisfactorily fit the individual IR SEDs as well as the composite UV to mid-IR composite SEDs. Given the success of these fits, we characterize the possible infrared SED of AGN polar dust emission and utilize a simple but effective strategy to infer its prevalence among type-1 AGNs. The SEDs of high-z peculiar AGNs, including the extremely red quasars, mid-IR warm-excess AGNs, and hot dust-obscured galaxies, can be also reproduced by our model. These results indicate that the IR SEDs of most AGNs, regardless of redshift or luminosity, arise from similar circumnuclear torus properties but differ mainly due to the optical depths of extended obscuring dust components.

The cigar distribution of suprathermal electrons (40–200 keV), showing electron pitch angles primarily in the parallel and anti-parallel directions, has been frequently observed in the terrestrial magnetotail. The formation of such a distribution is typically attributed to Fermi acceleration, betatron cooling, or a combination of these. To date, Fermi acceleration has been well studied via both observations and simulations, while betatron cooling has not been verified directly. In this study, we focus on the betatron cooling of suprathermal electrons. By analyzing a unique case observed by the Cluster spacecraft in the Earth's magnetotail (X_GSM ≈ −15 R_E), we find a significant drop of electron flux in association with the decrease of magnetic field strength, i.e., a magnetic dip. This magnetic dip is formed due to the expansion of flux tubes driven by two opposite flows. The drop in electron flux, primarily in the perpendicular direction, is therefore strong evidence of betatron cooling. We successfully reproduce these processes using an analytical model.

Pulsars are highly magnetized rotating neutron stars (NSs) with a very stable rotation speed. Irrespective of their stable rotation rate, many pulsars have been observed to feature a sudden jump in the spin frequency, known as a pulsar glitch. The glitch phenomena are considered to be an exhibit of superfluidity of neutron matter inside the NS's crustal region. The magnitude of such a rapid change in rotation rate relative to the stable rotation frequency can quantify the ratio of the moment of inertia (MoI) of the crustal region to the total MoI of the star, also called the fractional moment of inertia (FMI). In this paper, we have calculated the FMI for different masses of a star using six different representative unified equations of state constructed under a relativistic mean field framework. We have performed an event-wise comparison of the FMI obtained from data with that from theoretically calculated values with and without considering the entrainment effect. It is found that larger glitches cannot be explained by the crustal FMI alone, even without entrainment.

The deuterated hydrogen molecule HD has been observed in a variety of cool molecular astrophysical environments. By virtue of its small dipole moment the HD molecule is believed to have played an important role in the cooling of the primordial gas in the formation of the first stars and galaxies. HD has also recently been proposed as a tracer of molecular hydrogen in protoplanetary disk evolution, providing a diagnostic for the total disk mass. Here we report benchmark computations of rotational quenching rate coefficients for HD in collisions with H₂ based on quantum coupled channel methods within the rigid rotor model, and validate them against full-dimensional rovibrational scattering formalism. It is found that the rigid rotor model yields accurate rate coeffiicents for rotational transitions in HD+H₂ collisions at astrophysically relevant kinetic temperatures. Results are reported using the most recent highly accurate interaction potentials for the H₂–H₂ system. We obtain excellent agreement with previous results of Schaefer for the most important Δj = ±1, ±2 transitions in HD induced by ortho- and para-H₂, but find significant differences with recent results of Sultanov et al. that employed the same interaction potential as the one adopted here.

Solar eruptions, mainly eruptive flares with coronal mass ejections, represent the most powerful drivers of space weather. Due to the low plasma-β nature of the solar corona, solar eruption has its roots in the evolution of the coronal magnetic field. Although various theoretical models of the eruptive magnetic evolution have been proposed, they still oversimplify the realistic process in observation, which shows a much more complex process due to the invisible complex magnetic environment. In this paper, we continue our study of a complex sigmoid eruption in solar active region 11283, which is characterized by a multipolar configuration embedding a null-point topology and a sigmoidal magnetic flux rope. Based on extreme ultraviolet observations, it has been suggested that a three-stage magnetic reconnection scenario might explain the complex flare process. Here we reproduce the complex magnetic evolution during the eruption using a data-constrained high-resolution magnetohydrodynamic (MHD) simulation. The simulation clearly demonstrates three reconnection episodes, which occurred in sequence in different locations in the corona. Through these reconnections, the initial sigmoidal flux rope breaks one of its legs, and quickly gives birth to a new tornado-like magnetic structure that is highly twisted and has multiple connections to the Sun due to the complex magnetic topology. The simulated magnetic field configuration and evolution are found to be consistent with observations of the corona loops, filaments, and flare ribbons. Our study demonstrates that significant insight into a realistic, complex eruption event can be gained by a numerical MHD simulation that is constrained or driven by observed data.

We build a comprehensive sample to statistically describe the properties of X-ray flashes (XRFs) and X-ray riches (XRRs) from the third Swift Burst Alert Telescope (BAT3) catalog of Gamma-ray bursts (GRBs). We obtain 81 XRFs, 540 XRRs, and 394 classical GRBs (C-GRBs). We statistically explore the different properties of the γ-ray prompt emission, the X-ray emission, the X-ray light-curve type, the association with supernovae (SNe), and the host galaxy properties for these sources. We confirm that most XRFs/XRRs are long GRBs with low values of peak energy ${E}_{\mathrm{peak}}^{\mathrm{obs}}$ and they are low-luminosity GRBs. XRFs, XRRs, and C-GRBs follow the same E_X,iso–E_γ,iso–E_peak,z correlations. Compared to the classical GRBs, XRFs are favorable to have the association with SN explosions. We do not find any significant differences of redshift distribution and host galaxy properties among XRFs, XRRs, and C-GRBs. We also discuss some observational biases and selection effects that may affect our statistical results. The GRB detectors with wide energy range and low energy threshold are expected for the XRF/XRR research in the future.

An exact solution of the Lemaître–Tolman–Bondi class is investigated as a possible model of the Schwarzschild-like black hole embedded in a nonstatic dust-filled universe for the three types of spatial curvature. The solution is obtained in comoving coordinates by means of the mass function method. It is shown that the central part of space contains a Schwarzschild-like black hole. The R–T structure of the resulting spacetime is built. It is shown that the solution includes both the Schwarzschild and Friedmann solutions as its natural limits. The geodesic equations for test particles are analyzed. The particle observable velocities are found. The trajectories of the test particles are built from the point of view of both comoving and distant observers. For the distant observer, the results coincide with the Schwarzschild picture within a second-order accuracy near the symmetry center.

One bottleneck for the exploitation of data from the Kepler mission for stellar astrophysics and exoplanet research has been the lack of precise radii and evolutionary states for most of the observed stars. We report revised radii of 177,911 Kepler stars derived by combining parallaxes from the Gaia Data Release 2 with the DR25 Kepler Stellar Properties Catalog. The median radius precision is ≈8%, a typical improvement by a factor of 4–5 over previous estimates for typical Kepler stars. We find that ≈67% (≈120,000) of all Kepler targets are main-sequence stars, ≈21% (≈37,000) are subgiants, and ≈12% (≈21,000) are red giants, demonstrating that subgiant contamination is less severe than some previous estimates and that Kepler targets are mostly main-sequence stars. Using the revised stellar radii, we recalculate the radii for 2123 confirmed and 1922 candidate exoplanets. We confirm the presence of a gap in the radius distribution of small, close-in planets, but find that the gap is mostly limited to incident fluxes >200 ${F}_{\oplus }$, and its location may be at a slightly larger radius (closer to ≈2 R_⊕) when compared to previous results. Furthermore, we find several confirmed exoplanets occupying a previously described "hot super-Earth desert" at high irradiance, show the relation between a gas-giant planet's radius and its incident flux, and establish a bona fide sample of eight confirmed planets and 30 planet candidates with ${R}_{{\rm{p}}}$ < 2 R_⊕ in circumstellar "habitable zones" (incident fluxes between 0.25 and 1.50 ${F}_{\oplus }$). The results presented here demonstrate the potential for transformative characterization of stellar and exoplanet populations using Gaia data.

New Very Large Array (VLA) detections of the variable radio continuum source VLA J181335.1−174957, associated with the energetic X-ray pulsar PSR J1813−1749 and the TeV source HESS J1813–178, are presented. The radio source has a right circular polarization of ∼50% and a negative spectral index of −1.3 ± 0.1, which show that it is nonthermal. The radio pulses of the pulsar are not detected from additional Effelsberg observations at 1.4 GHz made within one week of a VLA detection. This result would appear to support the idea that the continuum radio emission detected with the VLA does not trace the time-averaged emission pulses, as had previously been suggested. We discuss other possible origins for the radio source, such as a pulsar wind, magnetospheric emission, and a low-mass star companion. However, observations made at higher frequencies by Camilo et al. show that the VLA source is in fact the time-averaged pulsed emission and that the detection of the pulses had not been achieved because this is the most scattered pulsar known.

It is noted that the duration of a fast radio burst (FRB), about 10⁻³ s, is a smaller fraction of the time delay between multiple images of a source gravitationally lensed by a galaxy or galaxy cluster than the human lifetime is to the age of the universe. Thus repeating, strongly lensed FRBs may offer an unprecedented opportunity for observing cosmological evolution in "real time." The possibility is discussed of observing cosmic expansion, transverse proper motion, mass accretion, and perhaps growth of density perturbations, as a function of redshift.

The TeV blazar Ton 599 has exhibited a peculiar flare in 2017 November. The temporal variation of the source is studied using simultaneous γ-ray data from the Fermi Large Area Telescope and radio data from the Owens Valley Radio Observatory's 40 m telescope, over the period of 9 yr. Four major flaring periods are observed in the γ-ray energy band of 0.1–300 GeV. These periods are studied on a shorter timescale and modeled with a time-dependent function containing exponential rising and decaying components. The physical parameters of the jet are estimated numerically and compared with those reported in the literature. During the fourth flare, a bunch of high-energy photons (>10 GeV) were detected. The two highest-energy photons, with energies of 76.9 and 61.9 GeV, are detected on MJD 58,059.0 and 58,073.3, respectively. This observation possibly constrains the γ-ray emission region to lie near the outer edge or outside the broad-line region of size ∼0.08 pc. The variation of equivalent width of an Mg ii line is studied using the spectroscopic data from Steward Observatory. It was observed that the equivalent width of the line varies inversely with the underlying power-law continuum.

We present 1201 galaxies at 0.05 < z < 0.45 that host tidal features in the first ∼200 deg² of imaging from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We select these galaxies from a sample of 21,208 galaxies with spectroscopic redshifts drawn from the Sloan Digital Sky Survey (SDSS) spectroscopic campaigns. Of these galaxies, we identify 214 shell systems and 987 stream systems. For 575 of these systems, we are additionally able to measure the (g−i) colors of the tidal features. We find evidence for star formation in a subset of the streams, with the exception of streams around massive ellipticals, and find that stream host galaxies span the full range of stellar masses in our sample. Galaxies that host shells are predominantly red and massive: we find that observable shells form more frequently around ellipticals than around disk galaxies of the same stellar mass. Although the majority of the shells in our sample are consistent with being formed by minor mergers, 15% ± 4.4% of shell host galaxies have (g−i) colors as red as their host galaxy, consistent with being formed by major mergers. These "red shell" galaxies are preferentially aligned with the major axis of the host galaxy, as previously predicted from simulations. We suggest that although the bulk of the observable shell population originates from fairly minor mergers, which preferentially form shells that are not aligned with the major axis of the galaxy, major mergers produce a significant number of observable shells.

We present empirical evidence, supported by a planet formation model, to show that the curve $R/{R}_{\oplus }=1.05{(F/{F}_{\oplus })}^{0.11}$ approximates the location of the so-called photo-evaporation valley. Planets below that curve are likely to have experienced complete photo-evaporation, and planets just above it appear to have inflated radii; thus we identify a new population of inflated super-Earths and mini-Neptunes. Our N-body simulations are set within an evolving protoplanetary disk and include prescriptions for orbital migration, gas accretion, and atmospheric loss due to giant impacts. Our simulated systems broadly match the sizes and periods of super-Earths in the Kepler catalog. They also reproduce the relative sizes of adjacent planets in the same system, with the exception of planet pairs that straddle the photo-evaporation valley. This latter group is populated by planet pairs with either very large or very small size ratios (R_out/R_in ≫ 1 or R_out/R_in ≪ 1) and a dearth of size ratios near unity. It appears that this feature could be reproduced if the planet outside the photo-evaporation valley (typically the outer planet, but sometimes not) has its atmosphere significantly expanded by stellar irradiation. This new population of planets may be ideal targets for future transit spectroscopy observations with the upcoming James Webb Space Telescope.

The origin of the so-called p-isotopes ${}^{\mathrm{92,94}}\mathrm{Mo}$ and ${}^{\mathrm{96,98}}\mathrm{Ru}$ in the solar system remains a mystery, as several astrophysical scenarios fail to account for them. In addition, data on presolar silicon carbide grains of type X (SiC X) exhibit peculiar Mo patterns, especially for ${}^{\mathrm{95,97}}\mathrm{Mo}$. We examine the production of Mo and Ru isotopes in neutrino-driven winds associated with core-collapse supernovae (CCSNe) over a wide range of conditions. We find that proton-rich winds can make dominant contributions to the solar abundance of ${}^{98}\mathrm{Ru}$ and significant contributions to those of ⁹⁶Ru, ⁹²Mo, and ⁹⁴Mo. In contrast, neutron-rich winds make negligible contributions to the solar abundances of ^92,94Mo and cannot produce ^96,98Ru, whereas the early ejecta of CCSNe can make dominant contributions to the solar abundance of ⁹²Mo. Furthermore, we show that some neutron-rich winds can account for the peculiar Mo patterns in SiC X grains. Our results can be generalized if conditions similar to those studied here are also obtained for other types of ejecta in either CCSNe or neutron star mergers.

Using observational data from the Magnetospheric Multiscale mission in the Earth's magnetosheath, we estimate the energy cascade rate at three ranges of length scale, employing a single data interval, using different techniques within the framework of incompressible magnetohydrodynamic (MHD) turbulence. At the energy-containing scale, the energy budget is controlled by the von Kármán decay law. Inertial range cascade is estimated by fitting a linear scaling to the mixed third-order structure function. Finally, we use a multi-spacecraft technique to estimate the Kolmogorov–Yaglom-like cascade rate in the kinetic range, well below the ion inertial length scale, where we expect a reduction due to involvement of other channels of transfer. The computed inertial range cascade rate is almost equal to the von Kármán–MHD law at the energy-containing scale, while the incompressive cascade rate evaluated at the kinetic scale is somewhat lower, as anticipated in theory. In agreement with a recent study, we find that the incompressive cascade rate in the Earth's magnetosheath is about 1000 times larger than the cascade rate in the pristine solar wind.

Studies of ultradense hydrogen H(0) in our laboratory have been reported in around 50 publications. The proton solar wind was shown to agree well with the protons ejected by Coulomb explosions in p(0). H(0) is a quantum material and can have at least two slightly different forms—ultradense protium p(0) and ultradense deuterium D(0)—which are stable even inside many stars. Mixed phases pD(0) have also been studied. These phases are the lowest-energy forms of hydrogen, and H(0) will probably exist everywhere where hydrogen exists in the universe. Rotational spectra from H(0) have been studied in laboratory experiments in emission in the visible range, giving good agreement with observations of ERE (extended red emission) in space. The ERE bands and sharp peaks agree with rotational transitions for a few coupled p–p and p–D pairs in the well studied spin state s = 4 in H(0). Since ERE is observed almost everywhere in space, this proves that H(0) is common in space. The rotational absorption from the ground state in p(0) agrees with the 220 nm extinction bump for three coupled p–p pairs in the most common spin state s = 2 studied. The uneven distribution of deuterium in space may be due to the slightly different properties of D(0), which separate it from p(0). The dark "missing mass" concluded to exist in the halos of rotating galaxies is proposed as being due to accumulation of H(0) there. Other important implications of the superfluid and superconductive phase H(0) in space await discovery.

The most heavily polluted white dwarfs often show excess infrared radiation from circumstellar dust disks, which are modeled as a result of tidal disruption of extrasolar minor planets. Interaction of dust, gas, and disintegrating objects can all contribute to the dynamical evolution of these dust disks. Here, we report two infrared variable dusty white dwarfs, SDSS J1228+1040 and G29-38. For SDSS J1228+1040, compared to the first measurements in 2007, the IRAC [3.6] and [4.5] fluxes decreased by 20% before 2014 to a level also seen in the recent 2018 observations. For G29-38, the infrared flux of the 10 μm silicate emission feature became 10% stronger between 2004 and 2007, We explore several scenarios that could account for these changes, including tidal disruption events, perturbation from a companion, and runaway accretion. No satisfactory causes are found for the flux drop in SDSS J1228+1040 due to the limited time coverage. Continuous tidal disruption of small planetesimals could increase the mass of small grains and concurrently change the strength of the 10 μm feature of G29-38. Dust disks around white dwarfs are actively evolving and we speculate that there could be different mechanisms responsible for the temporal changes of these disks.

The observation of the IceCube-170922A event from the direction of TXS 0506+056 when it was in its enhanced γ-ray emission state offers a unique opportunity to investigate the lepto-hadronic processes in blazar jets. Here, the observed broadband emission of TXS 0506+056 is explained by boosted synchrotron/synchrotron self Compton emission from the jet, whereas the γ-ray data observed during the neutrino emission by inelastic interactions of the jet-accelerated protons in a dense gaseous target. The proton energy distribution is $\sim {E}_{p}^{-2.50}$, calculated straightforwardly from the data obtained by the Fermi Large Area Telescope (Fermi-LAT) and the Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC); if such a distribution continues up to E_c,p = 10 PeV, the expected neutrino rate is as high as ∼0.46 events during the long active phase of the source or ∼0.15 if the activity lasts 60 days. In this interpretation, the energy content of the protons above >GeV in blazar jets can be estimated as well: the required proton injection luminosity is ≃2.0 × 10⁴⁸ erg s⁻¹ exceeding 10³ times that of electrons ≃10⁴⁵ erg s⁻¹, which are in equipartition with the magnetic field. As the required parameters are physically realistic, this can be an acceptable model for an explanation of the neutrino and γ-ray emission from TXS 0506+056.

The Atacama Large Millimeter/submillimeter Array (ALMA) has found multiple dust gaps and rings in a number of protoplanetary disks in continuum emission at millimeter wavelengths. The origin of such structures is under debate. Recently, we documented how one super-Earth planet can open multiple (up to five) dust gaps in a disk with low viscosity (α ≲ 10⁻⁴). In this paper, we examine how the positions, depths, and total number of gaps opened by one planet depend on input parameters, and apply our results to real systems. Gap locations (equivalently, spacings) are the easiest metric to use when making comparisons between theory and observations, as positions can be robustly measured. We fit the locations of gaps empirically as functions of planet mass and disk aspect ratio. We find that the locations of the double gaps in HL Tau and TW Hya, and of all three gaps in HD 163296, are consistent with being opened by a sub-Saturn mass planet. This scenario predicts the locations of other gaps in HL Tau and TW Hya, some of which appear consistent with current observations. We also show how the Rossby wave instability may develop at the edges of several gaps and result in multiple dusty vortices, all caused by one planet. A planet as low in mass as Mars may produce multiple dust gaps in the terrestrial planet-forming region.

For dark matter (DM) particles with masses in the 0.6–6m_p range, we set stringent constraints on the interaction cross-sections for scattering with ordinary baryonic matter. These constraints follow from the recognition that such particles can be captured by—and thermalized within—the Earth, leading to a substantial accumulation and concentration of DM that interact with baryons. Here, we discuss the probability that DM intercepted by the Earth will be captured, the number of DM particles thereby accumulated over Earth's lifetime, the fraction of such particles retained in the face of evaporation, and the density distribution of such particles within the Earth. In the latter context, we note that a previous treatment of the density distribution of DM, presented by Gould and Raffelt and applied subsequently to DM in the Sun, is inconsistent with considerations of hydrostatic equilibrium. Our analysis provides an estimate of the DM particle density at Earth's surface, which may exceed 10¹⁴ cm⁻³, and leads to constraints on various scattering cross-sections, which are placed by (1) the lifetime of the relativistic proton beam at the Large Hadron Collider; (2) the orbital decay of spacecraft in low Earth orbit; (3) the vaporization rate of cryogenic liquids in well-insulated storage dewars; and (4) the thermal conductivity of Earth's crust. For the scattering cross-sections that were invoked recently in Barkana's original explanation for the anomalously deep 21 cm absorption reported by EDGES, DM particle masses in the 0.6–4m_p range are excluded.

We present optical long-slit spectroscopy and far-ultraviolet to mid-infrared spectral energy distribution fitting of two diffuse dwarf galaxies, LSBG-285 and LSBG-750, which were recently discovered by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We measure redshifts using Hα line emission and find that these galaxies are at comoving distances of ≈25 and ≈41 Mpc, respectively, after correcting for the local velocity field. They have effective radii of r_eff = 1.2 and 1.8 kpc and stellar masses of M_⋆ ≈ (2–3) × 10⁷M_⊙. There are no massive galaxies (${M}_{\star }\gt {10}^{10}\,{M}_{\odot }$) within a comoving separation of at least 1.5 Mpc from LSBG-285 and 2 Mpc from LSBG-750. These sources are similar in size and surface brightness to ultradiffuse galaxies, except they are isolated, star-forming objects that were optically selected in an environmentally blind survey. Both galaxies likely have low stellar metallicities [Z_⋆/Z_⊙] < −1.0 and are consistent with the stellar mass–metallicity relation for dwarf galaxies. We set an upper limit on LSBG-750's rotational velocity of ∼50 km s⁻¹, which is comparable to dwarf galaxies of similar stellar mass with estimated halo masses <10¹¹M_⊙. We find tentative evidence that the gas-phase metallicities in both of these diffuse systems are high for their stellar mass, though a statistically complete, optically selected galaxy sample at very low surface brightness will be necessary to place these results into context with the higher surface brightness galaxy population.

Photo-/ion-induced ionization and dissociation processes are commonly observed for polycyclic aromatic hydrocarbon (PAH) molecules. This work performs theoretical studies of PAHs and their fragments. Molecular dynamics simulations in combination with static quantum chemical calculations reveal that following a single hydrogen atom loss, the fragments, PAH-H, are extremely reactive. They catch a neighbor molecule within picoseconds to form a covalently bonded large molecule regardless of orientations/angles and temperatures. We calculate the infrared spectra of the covalently bonded molecules, which indicate that such species could be the carrier of unidentified infrared emission bands. It also implies that regular PAHs might be less abundant in space than what is expected.

A magnetohydrodynamic (MHD) fluid description is typically employed to study the magnetized plasma comprising the solar atmosphere. This approach has had many successes in modeling and explaining solar phenomena. Most often, the plasma is assumed to be fully ionized. While this approach is justified in the higher atmosphere, i.e., the solar corona; the temperature in the lower solar atmosphere is such that a large proportion of the fluid may be electrically neutral. This begs the question: to what degree are the results derived from a fully ionized MHD description valid? In this article, we investigate the effect of partial ionization on buoyancy-driven MHD waves (the MHD analog of internal gravity waves) by applying a simplified two-fluid description. We show that previously derived results may be applied, when the fluid is weakly ionized, if the ion–neutral collision frequency is high. We derive dispersion relations for buoyancy-driven MHD waves, which include correction factors and damping rates due to ion–neutral collisions.

The concept of the quasar main sequence is very attractive since it stresses correlations between various parameters and implies the underlying simplicity. In the optical plane defined by the width of the Hβ line and the ratio of the equivalent width of the Fe ii to Hβ observed objects form a characteristic pattern. In this paper we use a physically motivated model to explain the distribution of quasars in the optical plane. Continuum is modeled as an accretion disk with a hard X-ray power law uniquely tight to the disk at the basis of observational scaling, and the broad-line region distance is determined also from observational scaling. We perform the computations of the Fe ii and Hβ line production with the code CLOUDY. We have only six free parameters for an individual source, maximum temperature of accretion disk, Eddington ratio, cloud density, cloud column density, microturbulence, and iron abundance, and only the last four remain as global parameters in our modeling of the whole sequence. Our theoretically computed points cover well the optical plane part populated with the observed quasars, particularly if we allow for supersolar abundance of heavy elements. Explanation of the exceptionally strong Fe ii emitter requires stronger contribution from the dark sides of the clouds. Analyzing the way our model covers the optical plane, we conclude that there is no single simple driver behind the sequence, as neither Eddington ratio nor broadband spectrum shape plays the dominant role. Also, the role of the viewing angle in providing the dispersion of the quasar main sequence is apparently not as strong as expected.

Grain surface chemistry and its treatment in gas-grain chemical models is an area of large uncertainty. While laboratory experiments are making progress, there is still much that is unknown about grain surface chemistry. Further, the results and parameters produced by experiments are often not easily translated to the rate equation approach most commonly used in astrochemical modeling. It is possible that statistical methods can reduce the uncertainty in grain surface chemical networks. In this work, a simple model of grain surface chemistry in a molecular cloud is developed and a Bayesian inference of the reactions rates is performed through Markov Chain Monte Carlo sampling. Using observational data of the solid state abundances of major chemical species in molecular clouds, the posterior distributions for the rates of seven reactions producing CO, CO₂, CH₃OH, and H₂O are calculated in a form that is suitable for rate equation models. This represents a vital first step in the development of a method to infer reaction rates from observations of chemical abundances in astrophysical environments.

We present high-resolution (017 × 014) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the CO (6–5) line and 435 μm dust continuum emission within a ∼9'' × 9'' area centered on the nucleus of the galaxy NGC 5135. NGC 5135 is a well-studied luminous infrared galaxy that also harbors a Compton-thick active galactic nucleus (AGN). At the achieved resolution of 48 × 40 pc, the CO (6–5) and dust emissions are resolved into gas "clumps" along the symmetrical dust lanes associated with the inner stellar bar. The clumps have radii in the range of ∼45–180 pc and CO (6–5) line widths of ∼60–88 $\mathrm{km}\,{{\rm{s}}}^{-1}$. The CO (6–5) to dust continuum flux ratios vary among the clumps and show an increasing trend with the [Fe ii]/Brγ ratios, which we interpret as evidence for supernova-driven shocked gas providing a significant contribution to the CO (6–5) emission. The central AGN is undetected in continuum, nor is it detected in CO (6–5) if its line velocity width is no less than ∼ 40 $\mathrm{km}\,{{\rm{s}}}^{-1}$. We estimate that the AGN contributes at most 1% of the integrated CO (6–5) flux of 512 ± 24 Jy $\mathrm{km}\,{{\rm{s}}}^{-1}$ within the ALMA field of view, which in turn accounts for ∼32% of the CO (6–5) flux of the whole galaxy.

A Forbush decrease is a sudden decrease in cosmic-ray intensity caused by transient interplanetary disturbances. The substructure of an interplanetary counterpart of a coronal mass ejection (ICME) such as a shock sheath and/or a magnetic cloud independently contributes to cosmic-ray decrease, which is evident as a two-step decrease. Our earlier work has shown multistep decrease and recovery within the ICME-driven shock-sheath region. Further, we have suggested that the presence of a small-scale flux rope within the shock-sheath region causes a steady/gradual recovery in cosmic-ray intensity. Here, we demonstrate the presence of a planar magnetic structure (PMS) and small-scale flux rope within a single shock sheath of an ICME. The plot of the elevation (θ) versus azimuthal (ϕ) angle of the interplanetary magnetic field (IMF) is used for the identification of the PMS. The planarity, efficiency, and a plane-normal vector are estimated by employing a minimum variance analysis (MVA) technique, which confirmed the presence of the PMS. In addition, a 2D-hodogram method in conjunction with the MVA technique is utilized to identify the flux-rope structure and turbulent conditions in the corresponding ICME region. The observation in the visible suggests that the PMS region within the ICME shock sheath caused the decrease in the cosmic-ray flux observed at Earth. It has also been observed that the sharp variations in the IMF (i.e., turbulence) cause a decrease, whereas the flux-rope structure is responsible for the recovery of the CR flux. Further studies are needed to investigate their origins and to confirm their effects on space weather.

We present Keck/OSIRIS laser guide-star assisted adaptive optics (LGSAO) integral-field spectroscopy of [O iii] λ5007 nebular emission from 12 galaxies hosting optically faint (${ \mathcal R }$ = 20–25; $\nu \,{L}_{\nu }\sim {10}^{44}-{10}^{46}$ erg s⁻¹) active galactic nuclei (AGNs) at redshift z ∼ 2–3. In combination with deep Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) rest-frame optical imaging, Keck/MOSFIRE rest-optical spectroscopy, and Keck/KCWI rest-UV integral-field spectroscopy, we demonstrate that both the continuum and emission-line structures of these sources exhibit a wide range of morphologies, from compact, isolated point sources to double-AGN merging systems with extensive ∼50 kpc tidal tails. One of the 12 galaxies previously known to exhibit a proximate damped Lyα system coincident in redshift with the galaxy shows evidence for both an extended [O iii] narrow-line emission region and spatially offset Lyα emission (with morphologically distinct blueshifted and redshifted components) indicative of large-scale gas flows photoionized by the central AGN. We do not find widespread evidence of star formation in the host galaxies surrounding these AGNs; the [O iii] velocity dispersions tend to be high (σ = 100–500 $\mathrm{km}\,{{\rm{s}}}^{-1}$), the continuum morphologies are much more compact than a mass-matched star-forming comparison sample, and the diagnostic nebular emission-line ratios are dominated by an AGN-like ionizing spectrum. The sample is most consistent with a population of AGNs that radiate at approximately their Eddington limit and photoionize extended [O iii] nebulae whose characteristic sizes scale approximately as the square root of the AGN luminosity.

To achieve a fuller understanding of galaxy evolution, SED fitting can be used to recover quantities beyond stellar masses (M_*) and star formation rates (SFRs). We use star formation histories (SFHs) reconstructed via the Dense Basis method of Iyer & Gawiser for a sample of 17,873 galaxies at 0.5 < z < 6 in the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey GOODS-S field to study the nature and evolution of the SFR–M_* correlation. The reconstructed SFHs represent trajectories in SFR–M_* space, enabling us to study galaxies at epochs earlier than observed by propagating them backward in time along these trajectories. We study the SFR–M_* correlation at z = 1, 2, 3, 4, 5, 6 using both direct fits to galaxies observed at those epochs and SFR–M_* trajectories of galaxies observed at lower redshifts. The SFR–M_* correlations obtained using the two approaches are found to be consistent with each other through a K-S test. Validation tests using SFHs from semi-analytic models and cosmological hydrodynamical simulations confirm the sensitivity of the method to changes in the slope, normalization, and shape of the SFR–M_* correlation. This technique allows us to further probe the low-mass regime of the correlation at high z by ∼1 dex and over an effective volume of ∼10× larger than possible with just direct fits. We find that the SFR–M_* correlation is consistent with being linear down to M_* ∼ 10⁶M_⊙ at z > 4. The evolution of the correlation is well described by $\mathrm{log}\,\mathrm{SFR}=(0.80\pm 0.029-0.017\pm 0.010\times {t}_{\mathrm{univ}})$$\mathrm{log}\,{M}_{* }-(6.487\pm 0.282-0.039\pm 0.008\times {t}_{\mathrm{univ}})$, where t_univ is the age of the universe in Gyr.

We report the discovery of 30 stars with extreme space velocities (≳480 $\,\mathrm{km}\,{{\rm{s}}}^{-1}$) in the Gaia-DR2 archive. These stars are a subset of 1743 stars with high-precision parallax, large tangential velocity (v_tan > 300 $\,\mathrm{km}\,{{\rm{s}}}^{-1}$), and measured line-of-sight velocity in DR2. By tracing the orbits of the stars back in time, we find at least one of them is consistent with having been ejected by the supermassive black hole at the Galactic Center. Another star has an orbit that passed near the Large Magellanic Cloud about 200 Myr ago. Unlike previously discovered blue hypervelocity stars, our sample is metal-poor (−1.5 < [Fe/H] < −1.0) and quite old (>1 $\,\mathrm{Gyr}$). We discuss possible mechanisms for accelerating old stars to such extreme velocities. The high observed space density of this population, relative to potential acceleration mechanisms, implies that these stars are probably bound to the Milky Way (MW). If they are bound, the discovery of this population would require a local escape speed of around ∼600 $\,\mathrm{km}\,{{\rm{s}}}^{-1}$ and consequently imply a virial mass of M₂₀₀ ∼ 1.4 × 10¹²M_⊙ for the MW.

We present X-ray timing results of the new black hole candidate MAXI J1535−571 during its 2017 outburst from Hard X-ray Modulation Telescope (Insight-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by Belloni, we find that the source exhibits transitions from the low/hard state to the hard intermediate state, and eventually to the soft intermediate state. Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of Insight-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV, which has rarely been explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lag) and strongly correlated with the centroid frequency. Assuming a geometrical origin of type-C QPOs, the source is consistent with being a high-inclination system.

Mrk 590 was originally classified as a Seyfert 1 galaxy, but then it underwent dramatic changes: the nuclear luminosity dropped by over two orders of magnitude and the broad emission lines all but disappeared from the optical spectrum. Here we present follow-up observations to the original discovery and characterization of this "changing-look" active galactic nucleus (AGN). The new Chandra  and Hubble Space Telescope observations from 2014 show that Mrk 590 is awakening, changing its appearance again. While the source continues to be in a low state, its soft excess has re-emerged, though not to the previous level. The UV continuum is brighter by more than a factor of two and the broad Mg ii emission line is present, indicating that the ionizing continuum is also brightening. These observations suggest that the soft excess is not due to reprocessed hard X-ray emission. Instead, it is connected to the UV continuum through warm Comptonization. Variability of the Fe Kα emission lines suggests that the reprocessing region is within ∼10 lt-yr or 3 pc of the central source. The change in AGN type is neither due to obscuration nor due to one-way evolution from Type 1 to Type 2, as suggested in the literature, but may be related to episodic accretion events.

The NuSTAR observatory, with its high sensitivity in hard X-rays, has enabled detailed broadband modeling of the X-ray spectra of active galactic nuclei (AGNs), thereby allowing constraints to be placed on the high-energy cutoff of the X-ray coronal continuum. We investigate the spectral properties of a sample of 46 NuSTAR-observed Seyfert 1 AGNs selected from the Swift/Burst Alert Telescope 70 month hard X-ray survey. Our measurements of the high-energy cutoff of the continuum from modeling the NuSTAR X-ray spectra are used to map out the temperature–compactness (θ–l) plane for AGN coronae. We find that most of the coronae lie clustered near the boundary for runaway pair production, suggesting that annihilation and pair production act to regulate the temperature of the corona. We discuss the implications of coronae whose high-energy cutoff may indicate a low coronal temperature on the heating and thermalization mechanisms in the corona.

We present the first X-ray and UV/optical observations of a very bright and fast nova in the disk of M31, M31N 2013-01b. The nova reached a peak magnitude R ∼ 15 mag and decayed by 2 mag in only 3 days, making it one of the brightest and fastest novae ever detected in Andromeda. From archival multiband data we have been able to trace its fast evolution down to U > 21 mag in less than two weeks and to uncover for the first time the super-soft X-ray phase, whose onset occurred 10–30 days from the optical maximum. The X-ray spectrum is consistent with a blackbody with a temperature of ∼50 eV and emitting radius of ∼4 × 10⁹ cm, larger than a white dwarf (WD) radius, indicating an expanded region. Its peak X-ray luminosity, 3.5 × 10³⁷ erg s⁻¹, places M31N 2013-01b among the most luminous novae in M31. We also unambiguously detect a short 1.28 ± 0.02 hr X-ray periodicity that we ascribe to the binary orbital period, possibly due to partial eclipses. This makes M31N 2013-01b the first nova in M31 with an orbital period determined. The short period also makes this nova one of the few known below the 2–3 hr orbital period gap. All of the observed characteristics strongly indicate that M31N 2013-01b harbors a massive WD and a very low mass companion, consistent with being a nova belonging to the disk population of the Andromeda galaxy.

Galaxies are surrounded by halos of hot gas whose mass and origin remain unknown. One of the most challenging properties to measure is the metallicity, which constrains both of these. We present a measurement of the metallicity around NGC 891, a nearby, edge-on, Milky Way analog. We find that the hot gas is dominated by low-metallicity gas near the virial temperature at ${kT}=0.20\pm 0.01\,\mathrm{keV}$ and $Z/{Z}_{\odot }=0.14\pm 0.03(\mathrm{stat}{)}_{-0.02}^{+0.08}(\mathrm{sys})$ and that this gas coexists with hotter (${kT}=0.71\pm 0.04\,\mathrm{keV}$) gas that is concentrated near the star-forming regions in the disk. Model choices lead to differences of ${\rm{\Delta }}Z/{Z}_{\odot }\sim 0.05$, and higher signal-to-noise ratio observations would be limited by systematic error and plasma emission model or abundance ratio choices. The low-metallicity gas is consistent with the inner part of an extended halo accreted from the intergalactic medium, which has been modulated by star formation. However, there is much more cold gas than hot gas around NGC 891, which is difficult to explain in either the accretion or supernova-driven outflow scenarios. We also find a diffuse nonthermal excess centered on the galactic center and extending to 5 kpc above the disk with a 0.3–10 keV ${L}_{{\rm{X}}}=3.1\times {10}^{39}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$. This emission is inconsistent with inverse Compton scattering or single-population synchrotron emission, and its origin remains unclear.

Recently, two-dimensional (2D) nonlinear instabilities of whistler waves from resonant wave–wave interaction have gained much attention in numerical simulations as well as observations in space plasmas. In this paper, both 2D and three-dimensional (3D) nonlinear instabilities of whistler waves are investigated using electron magnetohydrodynamics (EMHD). It is found that decay instabilities can excite waves with a broadband wavenumber spectrum, including highly oblique propagating whistler waves. Whistler waves with λ_ek = 1 would excite counter-propagating whistler waves, and the wave with ${\lambda }_{e}k\ne 1$ can produce both co- and counter-propagating whistler waves, where λ_e is the electron inertial length and k is the wavenumber. Moreover, it is shown that 3D instabilities have similar nonlinear growth rate distributions as in 2D decay for the azimuthal wavelength much larger than λ_e. These results suggest that nonlinear wave–wave interaction can play an important role in the scattering of whistler waves in the solar wind and the Earth's magnetosphere, and are also helpful for understanding nonlinear wave–wave interaction in the formation and development of EMHD turbulence.

The supernova remnant Cassiopeia A (Cas A) is one of the few remnants in which it is possible to observe unshocked ejecta. A deep 1.64 μm image of Cas A shows a patch of diffuse emission from unshocked ejecta, as well as brighter emission from fast-moving knots and quasi-stationary flocculi. Emission at 1.64 μm is usually interpreted as [Fe ii] emission, and spectra of the bright knots confirm this by showing the expected emission in other [Fe ii] lines. We performed near-infrared spectroscopy on the diffuse emission region and found that the unshocked ejecta emission does not show those lines, but rather shows the [Si i] 1.607 μm line. This means that the 1.64 μm line from the unshocked ejecta may be the [Si i] 1.645 line from the same upper level, rather than [Fe ii]. We find that the [Si i] line is formed by recombination, and we use the [Si i] to [Si ii] ratio to infer a temperature of about 100 K, which is close to the value assumed for an analysis of low-frequency radio absorption and that can be inferred from emission by cool dust. Our results constrain estimates of Cas A's total mass of unshocked ejecta that are extremely sensitive to temperature assumptions, but they do not resolve the ambiguity due to clumping.

Symbiotic stars often exhibit broad wings around Balmer emission lines, whose origin is still controversial. We present high-resolution spectra of the S type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS and the 3.6 m Canada–France–Hawaii Telescope to investigate the broad wings around Hα and Hβ. When Hα and Hβ lines are overplotted in the Doppler space, it is noted that Hα profiles are overall broader than Hβ in these two objects. Adopting a Monte Carlo approach, we consider the formation of broad wings of Hα and Hβ through Raman scattering of far-UV radiation around Lyβ and Lyγ and Thomson scattering by free electrons. Raman scattering wings are simulated by choosing an H i region with a neutral hydrogen column density N_{H i} and a covering factor CF. For Thomson wings, the ionized scattering region is assumed to fully cover the Balmer emission nebula and is characterized by the electron temperature T_e and the electron column density N_e. Thomson wings of Hα and Hβ have the same width that is proportional to ${T}_{{\rm{e}}}^{1/2}$. However, Raman wings of Hα are overall three times wider than Hβ counterparts, which is attributed to different cross sections for Lyβ and Lyγ. Normalized to have the same peak values and presented in the Doppler factor space, Hα wings of Z And and AG Dra are observed to be significantly wider than their Hβ counterparts, favoring the Raman scattering origin for broad Balmer wings.

Modeling the interface region between the solar photosphere and corona is challenging because the relative importance of magnetic and plasma forces change by several orders of magnitude. While the solar corona can be modeled by the force-free assumption, we need to take plasma forces into account (pressure gradient and gravity) in photosphere and chromosphere, here within the magnetohydrostatic (MHS) model. We solve the MHS equations with the help of an optimization principle and use vector magnetogram as the boundary condition. Positive pressure and density are ensured by replacing them with two new basic variables. The Lorentz force during optimization is used to update the plasma pressure on the bottom boundary, which makes the new extrapolation work even without pressure measurements on the photosphere. Our code is tested using a linear MHS model as reference. From the detailed analyses, we find that the newly developed MHS extrapolation recovers the reference model at high accuracy. The MHS extrapolation is, however, numerically more expensive than the nonlinear force-free field extrapolation and consequently one should limit their application to regions where plasma forces become important, e.g., in a layer of about 2 Mm above the photosphere.

1I/'Oumuamua is the first interstellar interloper to have been detected. Because planetesimal formation and ejection of predominantly icy objects are common by-products of the star and planet formation processes, in this study we address whether 1I/'Oumuamua could be representative of this background population of ejected objects. The purpose of the study of its origin is that it could provide information about the building blocks of planets in a size range that remains elusive to observations, helping to constrain planet formation models. We compare the mass density of interstellar objects inferred from its detection to that expected from planetesimal disks under two scenarios: circumstellar disks around single stars and wide binaries, and circumbinary disks around tight binaries. Our study makes use of a detailed study of the PanSTARRS survey volume; takes into account that the contribution from each star to the population of interstellar planetesimals depends on stellar mass, binarity, and planet presence; and explores a wide range of possible size distributions for the ejected planetesimals, based on solar system models and observations of its small-body population. We find that 1I/'Oumuamua is unlikely to be representative of a population of isotropically distributed objects, favoring the scenario that it originated from the planetesimal disk of a young nearby star whose remnants are highly anisotropic. Finally, we compare the fluxes of meteorites and micrometeorites observed on Earth to those inferred from this population of interstellar objects, concluding that it is unlikely that one of these objects is already part of the collected meteorite samples.

We explore the disk–jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of multiwavelength monitoring of the source. The target is unique in that its radiative output at radio wavelengths is dominated by a moderately beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96% and 98% respectively) between the optical and radio bands, with the disk lagging behind the jet by 250 ± 42 days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along a relativistic outflow. This scenario is supported by re-analysis of NuSTAR data, modeled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns an inner disk radius ${R}_{\mathrm{in}}/{R}_{\mathrm{ISCO}}={35}_{-16}^{+40}$. We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity L_bol ∼ 9 × 10⁴⁶ erg s⁻¹ ∼ 0.2L_Edd, the jet total kinetic energy L_j ∼ 4 × 10⁴⁴ erg s⁻¹, inferred from the dynamical modeling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.

We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-Hβ reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure Hβ time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent Hβ lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.

We studied dynamical balances in magnetorotational instability (MRI) turbulence with a net vertical field in the shearing box model of disks. Analyzing the turbulence dynamics in Fourier (${\boldsymbol{k}}$-)space, we identified three types of active modes that define the turbulence characteristics. These modes have lengths similar to the box size, i.e., lie in the small wavenumber region in Fourier space labeled "the vital area" and are (i) the channel mode, uniform in the disk plane with the smallest vertical wavenumber; (ii) the zonal flow mode, azimuthally and vertically uniform with the smallest radial wavenumber; and (iii) the rest (parasitic) modes. The rest modes comprise those harmonics in the vital area whose energies reach more than 50% of the maximum spectral energy. The rest modes individually are not so significant compared to the channel and zonal flow modes; however, the combined action of their multitude is dominant over these two modes. These three mode types are governed by the interplay of the linear and nonlinear processes, leading to their interdependent dynamics. The linear processes consist of disk flow nonmodality modified classical MRI with a net vertical field. The main nonlinear process is the transfer of modes over wavevector angles in Fourier space—the transverse cascade. The channel mode exhibits episodic bursts supplied by linear MRI growth, while the nonlinear processes mostly oppose this, draining the channel energy and redistributing it to the rest modes. As for the zonal flow, it does not have a linear source and is fed by nonlinear interactions of the rest modes.

Current and upcoming radio telescopes will map the spatial distribution of cosmic neutral hydrogen (H i) through its 21 cm emission. In order to extract the maximum information from these surveys, accurate theoretical predictions are needed. We study the abundance and clustering properties of H i at redshifts z ≤ 5 using TNG100, a large state-of-the-art magnetohydrodynamic simulation of a 75 h⁻¹ Mpc box size, which is part of the IllustrisTNG Project. We show that most of the H i lies within dark matter halos, and we provide fits for the halo H i mass function, i.e., the mean H i mass hosted by a halo of mass M at redshift z. We find that only halos with circular velocities larger than ≃30 km s⁻¹ contain H i. While the density profiles of H i exhibit a large halo-to-halo scatter, the mean profiles are universal across mass and redshift. The H i in low-mass halos is mostly located in the central galaxy, while in massive halos the H i is concentrated in the satellites. Our simulation reproduces the bias value of damped Lyα systems from observations. We show that the H i and matter density probability distribution functions differ significantly. Our results point out that for small halos, the H i bulk velocity goes in the same direction and has the same magnitude as the halo peculiar velocity, while in large halos, differences show up. We find that halo H i velocity dispersion follows a power law with halo mass. We find a complicated H i bias, with H i already becoming nonlinear at k = 0.3 h Mpc⁻¹ at z ≳ 3. The clustering of H i can, however, be accurately reproduced by perturbative methods. We find a new secondary bias by showing that the clustering of halos depends not only on mass but also on H i content. We compute the amplitude of the H i shot noise and find that it is small at all redshifts, verifying the robustness of BAO measurements with 21 cm intensity mapping. We study the clustering of H i in redshift space and show that linear theory can explain the ratio between the monopoles in redshift and real space down to 0.3, 0.5, and 1 h Mpc⁻¹ at redshifts 3, 4, and 5, respectively. We find that the amplitude of the Fingers-of-God effect is larger for H i than for matter, since H i is found only in halos above a certain mass. We point out that 21 cm maps can be created from N-body simulations rather than full hydrodynamic simulations. Modeling the one-halo term is crucial for achieving percent accuracy with respect to a full hydrodynamic treatment. Although our results are not converged against resolution, they are, however, very useful as we work at the resolution where the model parameters have been calibrated to reproduce galaxy properties.

Using a sample of four galaxy clusters at 1.35 < z < 1.65 and 10 galaxy clusters at 0.85 < z < 1.35, we measure the environmental quenching timescale, t_Q, corresponding to the time required after a galaxy is accreted by a cluster for it to fully cease star formation. Cluster members are selected by a photometric-redshift criterion, and categorized as star-forming, quiescent, or intermediate according to their dust-corrected rest-frame colors and magnitudes. We employ a "delayed-then-rapid" quenching model that relates a simulated cluster mass accretion rate to the observed numbers of each type of galaxy in the cluster to constrain t_Q. For galaxies of mass M_* ≳ 10^10.5M_⊙, we find a quenching timescale of t_Q = ${1.1}_{-0.3}^{+0.3}$ Gyr in the z ∼ 1.5 cluster sample, and ${t}_{{\rm{Q}}}={1.3}_{-0.3}^{+0.3}$ Gyr at z ∼ 1. Using values drawn from the literature, we compare the redshift evolution of t_Q to timescales predicted for different physical quenching mechanisms. We find t_Q to depend on host halo mass such that quenching occurs over faster timescales in clusters relative to groups, suggesting that properties of the host halo are responsible for quenching high-mass galaxies. Between z = 0 and z = 1.5, we find that t_Q evolves faster than the molecular gas depletion timescale and slower than an estimated star formation rate-outflow timescale, but is consistent with the evolution of the dynamical time. This suggests that environmental quenching in these galaxies is driven by the motion of satellites relative to the cluster environment, although due to uncertainties in the atomic gas budget at high redshift, we cannot rule out quenching due to simple gas depletion.

Relativistic effects dominate the emission of blazar jets, complicating our understanding of their intrinsic properties. Although many methods have been proposed to account for them, the variability Doppler factor method has been shown to describe the blazar populations best. We use a Bayesian hierarchical code called Magnetron to model the light curves of 1029 sources observed by the Owens Valley Radio Observatory's 40 m telescope as a series of flares with an exponential rise and decay, and estimate their variability brightness temperature. Our analysis allows us to place the most stringent constraints on the equipartition brightness temperature, i.e., the maximum achieved intrinsic brightness temperature in beamed sources, which we found to be $\langle {\text{}}{T}_{\mathrm{eq}}\rangle =2.78\times {10}^{11}\,{\rm{K}}\pm 26 \%$. Using our findings, we estimated the variability Doppler factor for the largest sample of blazars, increasing the number of available estimates in the literature by almost an order of magnitude. Our results clearly show that γ-ray loud sources have faster and higher amplitude flares than γ-ray quiet sources. As a consequence, they show higher variability brightness temperatures and thus are more relativistically beamed, with all of the above suggesting a strong connection between the radio flaring properties of the jet and γ-ray emission.

The correlation between the spins of dark matter halos and the large-scale structure (LSS) has been studied in great detail over a large redshift range, while investigations of galaxies are still incomplete. Motivated by this point, we use the state-of-the-art hydrodynamic simulation, Illustris-1, to investigate mainly the spin–LSS correlation of galaxies at a redshift of z = 0. We mainly find that the spins of low-mass, blue, oblate galaxies are preferentially aligned with the slowest collapsing direction (${{\boldsymbol{e}}}_{3}$) of the large-scale tidal field, while massive, red, prolate galaxy spins tend to be perpendicular to ${{\boldsymbol{e}}}_{3}$. The transition from a parallel to a perpendicular trend occurs at ∼10^9.4h⁻¹M_⊙ in the stellar mass, ∼0.62 in the g–r color, and ∼0.4 in triaxiality. The transition stellar mass decreases with increasing redshifts. The alignment was found to be primarily correlated with the galaxy stellar mass. Our results are consistent with previous studies both in N-body simulations and observations. Our study also fills the vacancy in the study of the galaxy spin–LSS correlation at z = 0 using hydrodynamical simulations and also provides important insight to understand the formation and evolution of galaxy angular momentum.

We present a long-exposure (∼10 hr), narrowband image of the supernova (SN) remnant Cassiopeia A (Cas A) centered at 1.644 μm emission. The passband contains [Fe ii] 1.644 μm and [Si i] 1.645 μm lines, and our "deep [Fe ii]+[Si i] image" provides an unprecedented panoramic view of Cas A, showing both shocked and unshocked SN ejecta, together with shocked circumstellar medium at subarcsecond (∼07 or 0.012 pc) resolution. The diffuse emission from the unshocked SN ejecta has a form of clumps, filaments, and arcs, and their spatial distribution correlates well with that of the Spitzer [Si ii] infrared emission, suggesting that the emission is likely due to [Si i] not [Fe ii] as in shocked material. The structure of the optically invisible western area of Cas A is clearly seen for the first time. The area is filled with many quasi-stationary flocculi (QSFs) and fragments of the disrupted ejecta shell. We identified 309 knots in the deep [Fe ii]+[Si i] image and classified them into QSFs and fast-moving knots (FMKs). The comparison with previous optical plates indicates that the lifetime of most QSFs is ≳60 yr. The total H+He mass of QSFs is ≈0.23 M_⊙, implying that the mass fraction of dense clumps in the progenitor's mass ejection immediately prior to the SN explosion is about 4%–6%. FMKs in the deep [Fe ii]+[Si i] image mostly correspond to S-rich ejecta knots in optical studies, while those outside the southeastern disrupted ejecta shell appear Fe-rich. The mass of the [Fe ii] line emitting, shocked dense Fe ejecta is ∼3 × 10⁻⁵M_⊙.

We report the result of optical identifications of FIRST radio sources with the Hyper Suprime-Cam Subaru Strategic Program survey (HSC-SSP). The positional cross-match within 1'' between the FIRST and HSC-SSP catalogs (i ≲ 26) produced more than 3600 optical counterparts in the 156 deg² of the HSC-SSP field. The matched counterparts account for more than 50% of the FIRST sources in the search field, which substantially exceed previously reported fractions of SDSS counterparts (i ≲ 22) of ∼30%. Among the matched sample, 9% are optically unresolved sources such as radio-loud quasars. The optically faint (i > 21) radio galaxies (RGs) show that the fitting linear function of the 1.4 GHz source counts has a slope that is flatter than that of the bright RGs, while optically faint radio quasars show a slope steeper than that of bright radio quasars. The optically faint RGs show a flat slope in the i-band number counts down to 24 mag, implying either less massive or distant radio-active galactic nuclei (AGNs) beyond 24 mag. The photometric redshift and the comparison of colors with the galaxy models show that most of the matched RGs are distributed at redshifts from 0 to 1.5. The optically faint sample includes the high radio-loudness sources that are not seen in the optically bright sample. Such sources are located at redshift z > 1. This study gives ∼1500 radio AGNs lying at the optically faint end and high-redshift regime not probed by previous searches.

On the basis of various data such as ALMA, JVLA, Chandra, Herschel, and Spitzer, we confirmed that two protostellar candidates in Oph A are bona fide protostars or proto-brown dwarfs (proto-BDs) in extremely early evolutionary stages. Both objects are barely visible across infrared (IR; i.e., near-IR to far-IR) bands. The physical nature of the cores is very similar to that expected in first hydrostatic cores (FHSCs), objects theoretically predicted in the evolutionary phase prior to stellar core formation with gas densities of ∼10^11–12 cm⁻³. This suggests that the evolutionary stage is close to the FHSC formation phase. The two objects are associated with faint X-ray sources, suggesting that they are in very early phase of stellar core formation with magnetic activity. In addition, we found the CO outflow components around both sources, which may originate from the young outflows driven by these sources. The masses of these objects are calculated to be ∼0.01–0.03 M_⊙ from the dust continuum emission. These physical properties are consistent with that expected from the numerical model of forming brown dwarfs. These facts (the X-ray detection, CO outflow association, and FHSC-like spectral energy distributions) strongly indicate that the two objects are proto-BDs or will be in the very early phase of protostars, which will evolve to more massive protostars if they gain enough mass from their surroundings. The ages of these two objects are likely to be within ∼10³ years after the protostellar core (or second core) formation, taking into account the outflow dynamical times (≲500 years).

It is believed that satellites of giant planets form in circumplanetary disks (CPDs). Many of the previous contributions assumed that their formation process proceeds similarly to rocky planet formation via accretion of the satellite seeds called satellitesimals. However, the satellitesimal formation itself poses a nontrivial problem, as the dust evolution in CPD is heavily impacted by fast radial drift and thus dust growth to satellitesimals is hindered. To address this problem, we connected state-of-the art hydrodynamical simulations of a CPD around a Jupiter-mass planet with dust growth, and a drift model in a post-processing step. We found that there is an efficient pathway to satellitesimal formation if there is a dust trap forming within the disk. Thanks to natural existence of an outward gas-flow region in the hydrodynamical simulation, a significant dust trap arises at the radial distance of 85 R_J from the planet, where the dust-to-gas ratio becomes high enough to trigger streaming instability. The streaming instability leads to efficient formation of the satellite seeds. Because of the constant infall of material from the circumstellar disk and the very short timescale of dust evolution, the CPD acts as a satellitesimal factory, constantly processing the infalling dust to pebbles that gather in the dust trap and undergo the streaming instability.

Vela X is a nearby pulsar wind nebula (PWN) powered by a ∼10⁴ year old pulsar. Modeling of the spectral energy distribution of the Vela X PWN has shown that accelerated electrons have largely escaped from the confinement, which is likely due to the disruption of the initially confined PWN by the supernova remnant reverse shock. The escaped electrons propagate to the Earth and contribute to the measured local cosmic-ray (CR) electron spectrum. We find that the escaped CR electrons from Vela X would hugely exceed the measured flux by High Energy Stereoscopic System (HESS) at ∼10 TeV if the standard diffusion coefficient for the interstellar medium (ISM) is used. We propose that the diffusion may be highly inefficient around Vela X and find that a spatially dependent diffusion can lead to CR flux that is consistent with the HESS measurement. Using a two-zone model for the diffusion around Vela X, we find that the diffusion coefficient in the inner region of a few tens of parsecs should be ≲10²⁸ cm² s⁻¹ for ∼10 TeV CR electrons, which is about two orders of magnitude lower than the standard value for the ISM. Such inefficient diffusion around PWN resembles the case of the Geminga and Monogem PWNe, suggesting that inefficient diffusion may be common in the vicinity of PWNe that span a wide range of ages.

The mass of single neutron stars (NSs) can be measured using astrometric microlensing events. In such events, the center-of-light motion of a star lensed by an NS will deviate from the expected nonlensed motion and this deviation can be used to measure the mass of the NS. I search for future conjunctions between pulsars, with measured proper motion, and stars in the GAIA-DR2 catalog. I identify two candidate events of stars involving lensing by a foreground pulsar in which the estimated light deflection of the background star will deviate from the nonlensed motion by more than 10 μas. PSR J185635−375435 passed ≅41 from a 19.4 G magnitude star on J2014.9 with an estimated deflection of 13 μas, while PSR J084606−353340 may pass ∼02 from a 19.0 G magnitude star on J2022.9 with an estimated deflection of 91 μas. However, the proper motion of the second event is highly uncertain. Therefore, additional observations are required in order to verify this event. I briefly discuss the opposite case, in which a pulsar is being lensed by a star. Such events can be used to measure the stellar mass via pulsar timing measurements. I do not find good candidates for such events with predicted variations in the pulsar period derivative ($\dot{P}$), divided by 1 s, exceeding 10⁻²⁰ s⁻¹. Since only about 10% of the known pulsars have measured proper motions, there is potential for an increase in the number of predicted pulsar lensing events.

The Carnegie–Chicago Hubble Program (CCHP) is recalibrating the extragalactic SN Ia distance scale using exclusively Population II stars. This effort focuses on the Tip of the Red Giant Branch (TRGB) method, whose systematics are entirely independent of the Population I Cepheid-based determinations that have long served as calibrators for the SN Ia distance scale. We present deep Hubble Space Telescope imaging of the low surface density and low line-of-sight reddening halos of two galaxies, NGC 1448 and NGC 1316, each of which have been hosts to recent SN Ia events. Provisionally anchoring the TRGB zero-point to the geometric distance to the Large Magellanic Cloud derived from detached eclipsing binaries, we measure extinction-corrected distance moduli of $31.23\pm {0.04}_{\mathrm{stat}}\pm {0.06}_{\mathrm{sys}}$ mag for NGC 1448 and $31.37\pm {0.04}_{\mathrm{stat}}\pm {0.06}_{\mathrm{sys}}$ mag for NGC 1316, respectively, giving metric distances of $17.7\pm {0.3}_{\mathrm{stat}}\pm {0.5}_{\mathrm{sys}}$ Mpc, and $18.8\pm {0.3}_{\mathrm{stat}}\pm {0.5}_{\mathrm{sys}}$ Mpc. We find agreement between our result and the available Cepheid distance for NGC 1448; for NGC 1316, where there are relatively few published distances based on direct measurements, we find that our result is consistent with the published SN Ia distances whose absolute scales are set from other locally determined methods such as Cepheids. For NGC 1448 and NGC 1316, our distances are some of the most precise (and systematically accurate) measurements with errors at 1.7 (2.8)% and 1.6 (2.7)% levels, respectively.

Information about the physical properties of astrophysical objects cannot be measured directly but is inferred by interpreting spectroscopic observations in the context of atomic physics calculations. Ratios of emission lines, for example, can be used to infer the electron density of the emitting plasma. Similarly, the relative intensities of emission lines formed over a wide range of temperatures yield information on the temperature structure. A critical component of this analysis is understanding how uncertainties in the underlying atomic physics propagate to the uncertainties in the inferred plasma parameters. At present, however, atomic physics databases do not include uncertainties on the atomic parameters and there is no established methodology for using them even if they did. In this paper we develop simple models for uncertainties in the collision strengths and decay rates for Fe xiii and apply them to the interpretation of density-sensitive lines observed with the EUV (extreme ultraviolet) Imagining spectrometer (EIS) on Hinode. We incorporate these uncertainties in a Bayesian framework. We consider both a pragmatic Bayesian method where the atomic physics information is unaffected by the observed data, and a fully Bayesian method where the data can be used to probe the physics. The former generally increases the uncertainty in the inferred density by about a factor of 5 compared with models that incorporate only statistical uncertainties. The latter reduces the uncertainties on the inferred densities, but identifies areas of possible systematic problems with either the atomic physics or the observed intensities.

We have computed a grid of theoretical models to fit the 12 oscillation modes of HIP 80088 observed by K2. HIP 80088 is determined to be a pre-main-sequence star, in which the CN cycle has not arrived at the equilibrium state. Mass fractions of C12 and N14 in metal composition are ${0.1277}_{-0.0049}^{+0.0064}$ and ${0.1092}_{-0.0074}^{+0.0057}$, respectively, indicating that 28% of C12 have turned into N14. Meanwhile, our fitting results show that physical parameters of HIP 80088 converge to a small range: M = 1.68–1.78 M_⊙, Z = 0.015–0.018, ${\upsilon }_{{\rm{e}}}=120\mbox{--}136$ km s⁻¹, log g = 4.114–4.125, R = 1.882–1.914 R_⊙, τ₀ = 7636–7723 s, and age = 9.03–10.21 Myr. Based on our model fittings, f₃ is suggested to be one radial mode, f₂, f₄, f₈, and f₁₁ to be four ℓ = 1 modes, and f₁, f₅, f₆, f₇, f₉, f₁₀, and f₁₂ to be seven ℓ = 2 modes. In particular, we find that (f₂, f₄, f₈) form one complete triplet with the averaged frequency spacing of 16.045 μHz, and (f₅, f₇, f₉, f₁₀) form four components of one quintuplet with the averaged frequency spacing of 13.388 μHz. The two averaged frequency spacings are not equal. Based on the best-fitting model, those ℓ = 2 modes of HIP 80088 are found to be mixed modes, which are p-dominated modes with pronounced g-mode features, while oscillation modes with ℓ = 1 are p modes.

I investigate an analytical model of galaxy clusters based on the assumptions that the intracluster medium plasma is polytropic and is in hydrostatic equilibrium. The Einasto profile is adopted as a model for the spatial-density distribution of dark matter halos. This model has sufficient degrees of freedom to simultaneously fit X-ray surface brightness and temperature profiles, with five parameters to describe the global cluster properties and three additional parameters to describe the cluster's cool-core feature. The model is tested with Chandra X-ray data for seven galaxy clusters, including three polytropic clusters and four cool-core clusters. It is found that the model accurately reproduces the X-ray data over most of the radial range. For all galaxy clusters, the data allows one to show that the model is essentially as good as that of Vikhlinin et al. and Bulbul et al., as inferred by the reduced χ².

We report the detection of 72 new pulses from the repeating fast radio burst FRB 121102 in Breakthrough Listen C-band (4–8 GHz) observations at the Green Bank Telescope. The new pulses were found with a convolutional neural network in data taken on 2017 August 26, where 21 bursts have been previously detected. Our technique combines neural network detection with dedispersion verification. For the current application, we demonstrate its advantage over a traditional brute-force dedispersion algorithm in terms of higher sensitivity, lower false-positive rates, and faster computational speed. Together with the 21 previously reported pulses, this observation marks the highest number of FRB 121102 pulses from a single observation, totaling 93 pulses in five hours, including 45 pulses within the first 30 minutes. The number of data points reveals trends in pulse fluence, pulse detection rate, and pulse frequency structure. We introduce a new periodicity search technique, based on the Rayleigh test, to analyze the time of arrivals (TOAs), with which we exclude with 99% confidence periodicity in TOAs with periods larger than 5.1 times the model-dependent timestamp uncertainty. In particular, we rule out constant periods ≳10 ms in the barycentric arrival times, though intrinsic periodicity in the time of emission remains plausible.

We have carried out observations in the 42–46 and 82–103 GHz bands with the Nobeyama 45 m radio telescope, and in the 338.2–339.2 and 348.45–349.45 GHz bands with the ASTE 10 m telescope, toward three high-mass star-forming regions containing massive young stellar objects (MYSOs), G12.89+0.49, G16.86−2.16, and G28.28−0.36. We have detected HC₃N including its ¹³C and D isotopologues, CH₃OH, CH₃CCH, and several complex organic molecules. Using our previous results for HC₅N in these sources, we compare their N(HC₅N)/N(CH₃OH) ratios. The ratio in G28.28−0.36 is derived to be ${0.091}_{-0.039}^{+0.109}$, which is higher than that in G12.89+0.49 by one order of magnitude, and higher than in G16.86−2.16 by a factor of ∼5. We investigate the relationship between the N(HC₅N)/N(CH₃OH) and the N(CH₃CCH)/N(CH₃OH) ratios. The relationships of the two column density ratios in G28.28−0.36 and G16.86−2.16 are similar to each other, while HC₅N is less abundant compared to CH₃CCH in G12.89+0.49. These results imply a chemical diversity in the lukewarm (T ∼ 20–30 K) envelope around MYSOs. In addition, several spectral lines from complex organic molecules, including very-high-excitation energy lines, have been detected toward G12.89+0.49, while the line density is significantly low in G28.28−0.36. These results suggest that organic-poor MYSOs are surrounded by a carbon-chain-rich lukewarm envelope (G28.28−0.36), while organic-rich MYSOs, namely hot cores, are surrounded by a CH₃OH-rich lukewarm envelope (G12.89+0.49 and G16.86−2.16).

There are important but unresolved processes in the standard formation scenarios of double compact star binaries (DCBs; black hole–black hole (BH–BH), BH–neutron star (BH–NS), NS–NS systems), such as mass transfer and the common envelope (CE) phase. We analyze the effects of different assumptions on key physical processes and binary initial conditions on massive star binary evolution with binary population synthesis (BPS), including a survey of proposed prescriptions for the mass transfer (q_cr) and the binding energy parameter (λ) in the CE phase. We find that q_cr clearly affects the properties of NS–NS systems while λ has an influence on the mass distributions of BH–BH systems. The merger rates of DCBs are increased by efficient CE ejection, which in our prescription is related to the binding energy parameter, including all the possible budgets to the energy content. It has been suggested that the difference in the properties of GW150914 and GW151226 may reflect different metallicity. We reproduce their properties with our BPS calculations and find that the property of BH–BH systems at low metallicity is sensitive to λ; the efficient CE ejection leads to a top-heavy mass distribution both for the primary and secondary BHs, which is favored to explain the nature of GW150914. The efficient CE ejection also leads to enhancement of both the BH–BH and NS–NS merger rates to the level consistent with the observational constraints from the detected gravitational-wave sources, including GW170817.

Rotating radio transients (RRATs) are a sub-class of pulsars characterized by sporadic emission and thus can generally only be studied by analysis of their single pulses. Here we present a single-pulse analysis using 11 years of timing data at 1400 MHz of three RRATs, PSRs J1819−1458, J1317−5759, and J1913+1330. We perform a spectral analysis on the single pulses of these RRATs for the first time, finding their mean spectral indices to be −1.1 ± 0.1, −0.6 ± 0.1, and −1.2 ± 0.2 respectively, within the known range of pulsar spectral indices. We find no evidence for narrowband features as seen for FRB 121102. However, we find the spread of single-pulse spectral indices for these RRATs (ranging from −7 to +4) to be larger than has been seen in other pulsars, with the exception of the Crab pulsar. We also analyze the time between detected pulses, or wait time, and find that the pulses are not random and cluster around wait times of a few pulse periods as well as ∼25 pulse periods for PSRs J1819−1458 and J1317−5759. Additionally we find that there is no correlation between the wait time and pulse flux density. Finally we find that the distribution of the pulse energy for PSRs J1317−5759 and J1913+1330 are log-normal, while that of PSR J1819−1458 is log-normal with possible evidence of an additional power-law component.

Non-local thermodynamical equilibrium (NLTE) line formation for Mg i and Mg ii lines is considered in classical 1D LTE model atmospheres of the Sun and 17 stars with reliable atmospheric parameters and in a broad range of spectral types: 3900 K ≤ ${T}_{\mathrm{eff}}$ ≤ 17,500 K, 1.1 ≤ log g ≤ 4.7, and −2.6 ≤ [Fe/H] ≤ +0.4. We find that, for each star, NLTE leads to smaller line-to-line scatter. For 10 stars, NLTE leads to consistent abundances of Mg i and Mg ii, while the difference in LTE abundance varies between −0.21 and +0.23 dex. We obtain an abundance discrepancy between Mg i and Mg ii in two very metal-poor stars, HD 140283 and HD 84937. The origin of these abundance differences remains unclear. Our standard NLTE modeling predicts Mg i emission lines at 7.736, 11.789, 12.224, and 12.321 μm in the atmospheres with ${T}_{\mathrm{eff}}$ ≤ 7000 K. We reproduce well the Mg i 12.2 and 12.3 μm emission lines in Procyon. However, for the Sun and three K-giants, the predicted Mg i emission lines are too weak compared with the observations. For stars with 7000 K ≤ ${T}_{\mathrm{eff}}$ ≤ 17,500 K, we recommend the Mg ii 3848, 3850, 4384, 4390, 4427, and 4433 Å lines for Mg abundance determinations even at the LTE assumption due to their small NLTE effects. The Mg i 4167, 4571, 4702, 5528, 5167, 5172, and 5183 Å lines can be safely used in the LTE analysis of stars with 7000 K < ${T}_{\mathrm{eff}}$ ≤ 8000 K. For the hotter stars, with ${T}_{\mathrm{eff}}$ from 8000 K to 9500 K, the NLTE effects are minor only for Mg i 4167, 4702, and 4528 Å.

Since its discovery as a pulsar in 2000, the central compact object (CCO) 1E 1207.4−5209 in the supernova remnant PKS 1209−51/52 had been a stable 0.424 s rotator with an extremely small spin-down rate and weak (${B}_{s}\approx 9\times {10}^{10}$ G) surface dipole magnetic field. In 2016 we observed a glitch from 1E 1207.4−5209 of at least ${\rm{\Delta }}f/f=(2.8\pm 0.4)\times {10}^{-9}$, which is typical in size for the general pulsar population. However, glitch activity is closely correlated with spin-down rate $\dot{f}$, and pulsars with $\dot{f}$ as small as that of 1E 1207.4−5209 are never seen to glitch. Unlike in glitches of ordinary pulsars, there may have been a large increase in $\dot{f}$ as well. The thermal X-ray spectrum of 1E 1207.4−5209, with its unique cyclotron absorption lines that measure the surface magnetic field strength, did not show any measurable change after the glitch, which rules out a major disruption in the dipole field as a cause or result of the glitch. A leading theory of the origin and evolution of CCOs, involving the prompt burial of the magnetic field by the fallback of supernova ejecta, might hold the explanation for the glitch.

The first nearby very-low-mass star–planet-host discovered, TRAPPIST-1, presents not only a unique opportunity for studying a system of multiple terrestrial planets, but a means to probe magnetospheric interactions between a star at the end of the main sequence and its close-in satellites. This encompasses both the possibility of persistent coronal solar-like activity, despite cool atmospheric temperatures, and the presence of large-scale magnetospheric currents, similar to what is seen in the Jovian system. Significantly, the current systems include a crucial role for close-in planetary satellites analogous to the role played by the Galilean satellites around Jupiter. We present the first radio observations of the seven-planet TRAPPIST-1 system using the Karl G. Jansky Very Large Array, looking for both highly circularly polarized radio emission and/or persistent quiescent emissions. We measure a broadband upper flux density limit of <8.1 μJy across 4–8 GHz, and place these observations both in the context of expectations for stellar radio emission, and the possible electrodynamic engines driving strong radio emissions in very-low-mass stars and brown dwarfs, with implications for future radio surveys of TRAPPIST-1 like planet-hosts. We conclude that the magnetic activity of TRAPPIST-1 is predominantly coronal and does not behave like the strong radio emitters at the stellar/substellar boundary. We further discuss the potential importance of magnetic field topology and rotation rates, demonstrating that a TRAPPIST-1 like planetary system around a rapidly rotating very-low-mass star can generate emission consistent with the observed radio luminosities of very-low-mass stars and brown dwarfs.

It is not known whether the original carriers of Earth's nitrogen were molecular ices or refractory dust. To investigate this question, we have used data and results of Herschel observations toward two protostellar sources: the high-mass hot core of Orion KL, and the low-mass protostar IRAS 16293−2422. Toward Orion KL, our analysis of the molecular inventory of Crockett et al. indicates that HCN is the organic molecule that contains by far the most nitrogen, carrying ${74}_{-9}^{+5} \%$ of nitrogen-in-organics. Following this evidence, we explore HCN toward IRAS 16293−2422, which is considered a solar analog. Toward IRAS 16293−2422, we have reduced and analyzed Herschel spectra of HCN, and fit these observations against "jump" abundance models of IRAS 16293−2422's protostellar envelope. We find an inner-envelope HCN abundance X_in = 5.9 ± 0.7 × 10⁻⁸ and an outer-envelope HCN abundance X_out = 1.3 ± 0.1 × 10⁻⁹. We also find the sublimation temperature of HCN to be T_jump = 71 ± 3 K; this measured T_jump enables us to predict an HCN binding energy E_B/k = 3840 ± 140 K. Based on a comparison of the HCN/H₂O ratio in these protostars to N/H₂O ratios in comets, we find that HCN (and, by extension, other organics) in these protostars is incapable of providing the total bulk N/H₂O in comets. We suggest that refractory dust, not molecular ices, was the bulk provider of nitrogen to comets. However, interstellar dust is not known to have ¹⁵N enrichment, while high ¹⁵N enrichment is seen in both nitrogen-bearing ices and in cometary nitrogen. This may indicate that these ¹⁵N-enriched ices were an important contributor to the nitrogen in planetesimals and likely to the Earth.

We investigate the value of the near-infrared imaging from upcoming surveys for constraining the ellipticities of galaxies. We select galaxies between 0.5 ≤ z < 3 that are brighter than expected Euclid sensitivity limits from the GOODS-S and N fields in CANDELS. The co-added CANDELS/HST V+I and J+H images are degraded in resolution and sensitivity to simulate Euclid-quality optical and near-infrared (NIR) images. We then run GALFIT on these simulated images and find that optical and NIR provide similar performances in measuring galaxy ellipticities at redshifts 0.5 ≤ z < 3. At z > 1.0, the NIR-selected source density is higher by a factor of 1.4 and therefore the standard error in NIR-derived ellipticities is about 30% smaller, implying a more precise ellipticity measurement. The good performance of the NIR is mainly because galaxies have an intrinsically smoother light distribution in the NIR bands than in the optical, the latter tracing the clumpy star-forming regions. In addition, the NIR bands have a higher surface brightness per pixel than the optical images, while being less affected by dust attenuation. Despite the worse spatial sampling and resolution of Euclid NIR compared to optical, the NIR approach yields equivalent or more precise galaxy ellipticity measurements. If systematics that affect shape such as dithering strategy and point-spread function undersampling can be mitigated, inclusion of the NIR can improve galaxy ellipticity measurements over all redshifts. This is particularly important for upcoming weak lensing surveys, such as with Euclid and WFIRST.

We report rest frequencies for rotational transitions of the deuterated ammonium isotopologues NH₃D⁺, NH₂D₂⁺, and NHD₃⁺, measured in a cryogenic ion trap machine. For the symmetric tops NH₃D⁺ and NHD₃⁺, one and three transitions are detected, respectively, and five transitions are detected for the asymmetric top NH₂D₂⁺. While the lowest frequency transition of NH₃D⁺ was already known in the laboratory and space, this work enables the future radio astronomical detection of the two other isotopologues.

We present Atacama Large Millimeter Array 1 mm observations of the rest-frame far-infrared (FIR) dust continuum in 27 quasars at redshifts 6.0 ≲ z < 6.7. We detect FIR emission at ≳3σ in all quasar host galaxies with flux densities at ∼1900 GHz in the rest-frame of 0.12 < S_{rest,1900 GHz} < 5.9 mJy, with a median (mean) flux density of 0.88 mJy (1.59 mJy). The implied FIR luminosities range from ${L}_{\mathrm{FIR}}$ = (0.27–13) × 10¹²${L}_{\odot }$, with 74% of our quasar hosts having ${L}_{\mathrm{FIR}}$ > 10¹²${L}_{\odot }$. The estimated dust masses are ${M}_{\mathrm{dust}}$ = 10⁷–10⁹${M}_{\odot }$. If the dust is heated only by star formation, then the star formation rates in the quasar host galaxies are between 50 and 2700 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$. In the framework of the host galaxy–black hole coevolution model a correlation between ongoing black hole growth and star formation in the quasar host galaxy would be expected. However, combined with results from the literature to create a luminosity-limited quasar sample, we do not find a strong correlation between quasar UV luminosity (a proxy for ongoing black hole growth) and FIR luminosity (star formation in the host galaxy). The absence of such a correlation in our data does not necessarily rule out the coevolution model, and could be due to a variety of effects (including different timescales for black hole accretion and FIR emission).

We present results from observations of the Galactic Center magnetar, PSR J1745–2900, at 2.3 and 8.4 GHz with the NASA Deep Space Network 70 m antenna, DSS-43. We study the magnetar's radio profile shape, flux density, radio spectrum, and single pulse behavior over a ∼1 year period between MJDs 57233 and 57621. In particular, the magnetar exhibits a significantly negative average spectral index of $\langle \alpha \rangle =-1.86\pm 0.02$ when the 8.4 GHz profile is single-peaked, which flattens considerably when the profile is double-peaked. We have carried out an analysis of single pulses at 8.4 GHz on MJD 57479 and find that giant pulses and pulses with multiple emission components are emitted during a significant number of rotations. The resulting single pulse flux density distribution is incompatible with a log-normal distribution. The typical pulse width of the components is ∼1.8 ms, and the prevailing delay time between successive components is ∼7.7 ms. Many of the single pulse emission components show significant frequency structure over bandwidths of ∼100 MHz, which we believe is the first observation of such behavior from a radio magnetar. We report a characteristic single pulse broadening timescale of $\langle {\tau }_{d}\rangle =6.9\pm 0.2\,\mathrm{ms}$ at 8.4 GHz. We find that the pulse broadening is highly variable between emission components and cannot be explained by a thin scattering screen at distances ≳ 1 kpc. We discuss possible intrinsic and extrinsic mechanisms for the magnetar's emission and compare our results to other magnetars, high magnetic field pulsars, and fast radio bursts.

We present the full disk-fit results VANDAM survey of all Class 0 and I protostars in the Perseus molecular cloud. We have 18 new protostellar disk candidates around Class 0 and I sources, which are well described by a simple, parametrized disk model fit to the 8 mm VLA dust continuum observations. 33% of Class 0 protostars and just 11% of Class I protostars have candidate disks, while 78% of Class 0 and I protostars do not have signs of disks within our 12 au disk diameter resolution limit, indicating that at 8 mm most disks in the Class 0 and I phases are <10 au in radius. These small radii may be a result of surface brightness sensitivity limits. Modeled 8 mm radii are similar to the radii of known Class 0 disks with detected Keplerian rotation. Since our 8 mm data trace a population of larger dust grains that radially drift toward the protostar and are lower limits on true disk sizes, large disks at early times do not seem to be particularly rare. We find statistical evidence that Class 0 and I disks are likely drawn from the same distribution, meaning disk properties may be defined early in the Class 0 phase and do not undergo large changes through the Class I phase. By combining our candidate disk properties with previous polarization observations, we find a qualitative indication that misalignment between inferred envelope-scale magnetic fields and outflows may indicate disks on smaller scales in Class 0 sources.

We analyze the properties of a sample of long gamma-ray bursts (LGRBs) detected by the Fermi satellite that have a spectroscopic redshift and good follow-up coverage at both X-ray and optical/near infrared wavelengths. The evolution of LGRB afterglows depends on the density profile of the external medium, enabling us to separate wind or interstellar medium (ISM)-like environments based on the observations. We do this by identifying the environment that provides the best agreement between estimates of p, the index of the underlying power-law distribution of electron energies, as determined by the behavior of the afterglow in different spectral/temporal regimes. At 11 rest-frame hours after trigger, we find a roughly even split between ISM-like and wind-like environments. We further find a 2σ separation in the prompt emission energy distributions of wind-like and ISM-like bursts. We investigate the underlying physical parameters of the shock, and calculate the (degenerate) product of density and magnetic field energy (_B). We show that _B must be $\ll {10}^{-2}$ to avoid implied densities comparable to the intergalactic medium. Finally, we find that the most precisely constrained observations disagree on p by more than would be expected based on observational errors alone. This suggests additional sources of error that are not incorporated in the standard afterglow theory. For the first time, we provide a measurement of this intrinsic error that can be represented as an error in the estimate of p of magnitude 0.25 ± 0.04. When this error is included in the fits, the number of LGRBs with an identified environment drops substantially, but the equal division between the two types remains.