Table of contents

Our ability to study the properties of the interstellar medium in the earliest galaxies will rely on emission-line diagnostics at rest-frame ultraviolet (UV) wavelengths. In this work, we identify metallicity-sensitive diagnostics using UV emission lines. We compare UV-derived metallicities with standard, well-established optical metallicities using a sample of galaxies with rest-frame UV and optical spectroscopy. We find that the He2–O3C3 diagnostic (He iiλ1640 ${\rm{\mathring{\rm A} }}$/C iii] λ1906,1909 ${\rm{\mathring{\rm A} }}$ versus [O iii] λ1666 ${\rm{\mathring{\rm A} }}$/C iii] λ1906,9 ${\rm{\mathring{\rm A} }}$) is a reliable metallicity tracer, particularly at low metallicity ($12+{\mathrm{log}}_{10}({\rm{O}}/{\rm{H}})\leqslant 8$), where stellar contributions are minimal. We find that the Si3–O3C3 diagnostic ([Si iii] λ1883 ${\rm{\mathring{\rm A} }}$/C iii] λ1906 ${\rm{\mathring{\rm A} }}$ versus [O iii] λ1666 ${\rm{\mathring{\rm A} }}$/C iii] λ1906,9 ${\rm{\mathring{\rm A} }}$) is a reliable metallicity tracer, though with large scatter (0.2–0.3 dex), which we suggest is driven by variations in gas-phase abundances. We find that the C4–O3C3 diagnostic (C ivλ 1548,50 ${\rm{\mathring{\rm A} }}$/[O iii] λ 1666 ${\rm{\mathring{\rm A} }}$ versus [O iii] λ 1666 ${\rm{\mathring{\rm A} }}$/C iii] λ 1906,9 ${\rm{\mathring{\rm A} }}$) correlates poorly with optically derived metallicities. We discuss possible explanations for these discrepant metallicity determinations, including the hardness of the ionizing spectrum, contribution from stellar wind emission, and non-solar-scaled gas-phase abundances. Finally, we provide two new UV oxygen abundance diagnostics, calculated from polynomial fits to the model grid surface in the He2–O3C3 and Si3–O3C3 diagrams.

Double degenerate (DD) systems are supposed to be significant gravitational-wave (GW) sources for future space-based GW detectors, e.g., the Laser Interferometer Space Antenna (LISA). Recently, one type of DD system with extremely low-mass WD (ELM WD; ≲ 0.30 M_☉) companions was found in the ELM Survey. These companions have very short orbital periods and are therefore important sources for LISA detection. Further, due to the thick envelope of ELM WDs compared with massive WDs (e.g., CO WDs), they are much easier to find through the combination of electromagnetic (EM) and GW observations. In this paper, we first obtain the population of ELM WDs in DDs by considering the detailed evolutionary tracks of ELM WDs and then analyzing the GW radiation of these systems. We found that about 6 × 10³ sources could be solely detected by LISA, including ∼2 × 10³ chirping sources, and ∼13 (∼107) more sources are expected to be detected by both LISA and the ELM Survey (Gaia).

One of the most unique phenomena in the Galactic center region is the existence of numerous long and narrow filamentary structures within a few hundred parsecs of Sgr A^⋆. While more than 100 radio filaments have been revealed by MeerKAT, only about two dozen X-ray filaments have been discovered so far. In this article, we report our analysis of deep Chandra and NuSTAR observations of a nonthermal X-ray filament, G0.13–0.11, which is located adjacent to the Radio Arc. Chandra revealed a unique morphology of G0.13–0.11, which is an elongated (0.1 pc in width and 3.2 pc in length) structure slightly bent toward the Radio Arc. A pulsar candidate (Γ ∼ 1.4) is detected in the middle of the filament, with a tail of diffuse nonthermal X-ray emission on one side of the filament. The filament is detected by NuSTAR up to 79 keV, with the hard X-ray centroid consistent with the pulsar candidate. We found that the X-ray intensity decays along the filament farther away from the pulsar candidate, dropping to half of its peak value 2.2 pc away. This system is most likely a pulsar wind nebula (PWN) interacting with the ambient interstellar magnetic field, where the filaments are kinetic jets from the PWN as recently proposed. The nature of this filament adds to the complex origin of X-ray filaments, which serve as powerful tools for probing local and global powerful particle accelerators in the Galactic center.

Ultracompact massive galaxies (ucmgs), i.e., galaxies with stellar masses ${M}_{\star }\gt 8\times {10}^{10}{M}_{\odot }$ and effective radii ${R}_{{\rm{e}}}\lt 1.5\,\mathrm{kpc}$, are very rare systems, in particular at low and intermediate redshifts. Their origin as well as their number density across cosmic time are still under scrutiny, especially because of the paucity of spectroscopically confirmed samples. We have started a systematic census of ucmg candidates within the ESO Kilo Degree Survey, together with a large spectroscopic follow-up campaign to build the largest possible sample of confirmed ucmgs. This is the third paper of the series and the second based on the spectroscopic follow-up program. Here, we present photometrical and structural parameters of 33 new candidates at redshifts $0.15\lesssim z\lesssim 0.5$ and confirm 19 of them as ucmgs, based on their nominal spectroscopically inferred ${M}_{\star }$ and ${R}_{{\rm{e}}}$. This corresponds to a success rate of $\sim 58 \%$, nicely consistent with our previous findings. The addition of these 19 newly confirmed objects allows us to fully assess the systematics on the system selection—and to finally reduce the number density uncertainties. Moreover, putting together the results from our current and past observational campaigns and some literature data, we build the largest sample of ucmgs ever collected, comprising 92 spectroscopically confirmed objects at $0.1\lesssim z\lesssim 0.5$. This number raises to 116, allowing for a 3σ tolerance on the ${M}_{\star }$ and ${R}_{{\rm{e}}}$ thresholds for the ucmg definition. For all these galaxies, we have estimated the velocity dispersion values at the effective radii, which have been used to derive a preliminary mass–velocity dispersion correlation.

The number of independent parameters that ultraviolet interstellar extinction curves depend on has never been decisively clarified, yet the issue is critical for the comprehension and modeling of interstellar extinction observations. Cardelli, Clayton, & Mathis (CCM89) concluded that normalized extinction curves rely on only one parameter, but E. Fitzpatrick and others consider this finding at most a first-order approximation favored by uncertainties in measurement. However, the multiparameter fits successively introduced by Fitzpatrick & Massa were intended to give the best possible analytical representation of extinction curves, not to investigate their degrees of freedom. A deeper examination of these fits and of the CCM89 conclusion shows that they do not necessarily conflict. Fitzpatrick & Massa's parameterization of extinction curves and the large database (nearly 600 directions) published by Krelowski & Strobel are used in this paper to show that, within the precision allowed by the data, E(λ − V) correlates tightly with E(B − V) for all λ within the near-infrared to far-ultraviolet spectrum. This correlation confirms the relationships that led to the CCM89 fit and calls into question the reliability of today's interstellar dust models, which all need at least seven parameters (reddening included) to fit observed ultraviolet extinction curves.

Fully kinetic two-dimensional particle-in-cell simulations are used to study electron acceleration at high-Mach-number nonrelativistic perpendicular shocks. Supernova remnant shocks are mediated by the Weibel instability, which is excited because of an interaction between shock-reflected and upstream ions. Nonlinear evolution of the Weibel instability leads to the formation of current sheets. At the turbulent shock ramp the current sheets decay through magnetic reconnection. The number of reconnection sites strongly depends on the ion-to-electron mass ratio and the Alfvénic Mach number of the simulated shock. Electron acceleration is observed at locations where magnetic reconnection operates. For the highest mass ratios almost all electrons are involved in magnetic reconnection, which makes the magnetic reconnection the dominant acceleration process for electrons at these shocks. We discuss the relevance of our results for 3D systems with realistic ion-to-electron mass ratio.

We investigated the quasi-periodic pulsation (QPP) in Lyα, X-ray, and extreme-ultraviolet (EUV) emissions during two solar flares, i.e., an X-class (SOL2012-01-27T) and a C-class (SOL2016-02-08T). The full-disk Lyα and X-ray flux during these solar flares were recorded by the EUV Sensor and X-Ray Sensor on board the Geostationary Operational Environmental Satellite. The flare regions were located from the EUV images measured by the Atmospheric Imaging Assembly. The QPP could be identified as a series of regular and periodic peaks in the light curves, and its quasi-periodicity was determined from the global wavelet and Fourier power spectra. A quasi-periodicity at about 3 minutes is detected during the impulsive phase of the X-class flare, which could be explained as the acoustic wave in the chromosphere. Interestingly, a quasi-periodicity at roughly 1 minute is discovered during the entire evolutionary phases of solar flares, including the precursor, impulsive, and gradual phases. This is the first report of 1 minute QPP in the Lyα emission during solar flares, in particular during the flare precursor. It may be interpreted as a self-oscillatory regime of the magnetic reconnection, such as magnetic dripping.

We present here the weak gravitational lensing detection of four nearby galaxy clusters in the southern sky: A2029, A85, A1606, and A2457. The weak lensing detections of A1606 and A2457 are the first in the literature. This work capitalizes on the wide field of view of the Dark Energy Camera at the Cerro Tololo Inter-American Observatory, which we use to obtain deep, multiwavelength imaging of all targets. We publish maps of the clusters' projected mass distributions and obtain the M₂₀₀ of their clusters through Navarro–Frenk–White profile fits to the 2D tangential ellipticity signal.

It is widely believed that magnetars could be born in core-collapse supernovae (SNe), binary neutron star (BNS) or binary white dwarf (BWD) mergers, or accretion-induced collapse (AIC) of white dwarfs. In this paper, we investigate whether magnetars could also be produced from neutron star–white dwarf (NSWD) mergers, motivated by FRB 180924-like fast radio bursts (FRBs) possibly from magnetars born in BNS/BWD/AIC channels suggested by Margalit et al. (2019). By a preliminary calculation, we find that NSWD mergers with unstable mass transfer could result in the NS acquiring an ultra-strong magnetic field via the dynamo mechanism due to differential rotation and convection or possibly via the magnetic flux conservation scenario of a fossil field. If NSWD mergers can indeed create magnetars, then such objects could produce at least a subset of FRB 180924-like FRBs within the framework of flaring magnetars, since the ejecta, local environments, and host galaxies of the final remnants from NSWD mergers resemble those of BNS/BWD/AIC channels. This NSWD channel is also able to well explain both the observational properties of FRB 180924-like and FRB 180916.J0158+65-like FRBs within a large range in local environments and host galaxies.

In the hierarchical structure formation model of the universe, galaxy clusters are assembled through a series of mergers. Accordingly, it is expected that galaxy clusters in the early universe are actively forming and dynamically young. Located at a high redshift of z = 1.71, SpARCS1049+56 offers a unique look into the galaxy cluster formation process. This cluster has been shown to be rich in cluster galaxies and to have intense star formation. Its high redshift pushes a weak-lensing analysis beyond the regime of the optical spectrum into that of the infrared. Equipped with deep Hubble Space Telescope Wide Field Camera 3 UVIS and IR observations, we present a weak-lensing characterization of SpARCS1049+56. As few IR weak-lensing studies have been performed, we discuss the details of point-spread function modeling and galaxy shape measurement for an IR weak-lensing procedure and the systematics that come with the territory. It will be critical to understand these systematics in future weak-lensing studies in the IR with the next-generation space telescopes such as the James Webb Space Telescope, Euclid, and WFIRST. Through a careful analysis, the mass distribution of this young galaxy cluster is mapped and the convergence peak is detected at a 3.3σ level. The weak-lensing mass of the cluster is estimated to be 3.5 ± 1.2 × 10¹⁴M_⊙ and is consistent with the mass derived from a mass–richness scaling relation. This mass is extreme for a cluster at such a high redshift and suggests that SpARCS1049+56 is rare in the standard ΛCDM universe.

Using data from the (intermediate) Palomar Transient Factory (iPTF), we characterize the time variability of ≈500 massive stars in M31. Our sample is those stars that are spectrally typed by Massey and collaborators, including Luminous Blue Variables, Wolf–Rayets, and warm and cool supergiants. We use the high-cadence, long-baseline (≈5 yr) data from the iPTF survey, coupled with data-processing tools that model complex features in the light curves. We find widespread photometric (R-band) variability in the upper Hertzsprung Russell diagram (or CMD) with an increasing prevalence of variability with later spectral types. Red stars (V − I > 1.5) exhibit larger amplitude fluctuations than their bluer counterparts. We extract a characteristic variability timescale, t_ch, via wavelet transformations that are sensitive to both continuous and localized fluctuations. Cool supergiants are characterized by longer timescales (>100 days) than the hotter stars. The latter have typical timescales of tens of days but cover a wider range, from our resolution limit of a few days to longer than 100 days. Using a 60 night block of data straddling two nights with a cadence of around 2 minutes, we extracted t_ch in the range 0.1–10 days with amplitudes of a few percent for 13 stars. Though there is broad agreement between the observed variability characteristics in the different parts of the upper CMD with theoretical predictions, detailed comparison requires models with a more comprehensive treatment of the various physical processes operating in these stars, such as pulsation, subsurface convection, and the effect of binary companions.

Due to its Earth-like minimum mass of 1.27 M_E and its close proximity to our solar system, Proxima Centauri b is one of the most interesting exoplanets for habitability studies. Its host star, Proxima Centauri, is however a strongly flaring star, which is expected to provide a very hostile environment for potentially habitable planets. We perform a habitability study of Proxima Centauri b assuming an Earth-like atmosphere under high stellar particle bombardment, with a focus on spectral transmission features. We employ our extensive model suite calculating energy spectra of stellar particles, their journey through the planetary magnetosphere, ionosphere, and atmosphere, ultimately providing planetary climate and spectral characteristics, as outlined in Herbst et al. Our results suggest that together with the incident stellar energy flux, high particle influxes can lead to efficient heating of the planet well into temperate climates, by limiting CH₄ amounts, which would otherwise run into antigreenhouse for such planets around M stars. We identify some key spectral features relevant for future spectral observations: First, NO₂ becomes the major absorber in the visible, which greatly impacts the Rayleigh slope. Second, H₂O features can be masked by CH₄ (near-infrared) and CO₂ (mid- to far-infrared), making them nondetectable in transmission. Third, O₃ is destroyed and instead HNO₃ features become clearly visible in the mid- to far-infrared. Lastly, assuming a few percent of CO₂ in the atmosphere, CO₂ absorption at 5.3 μm becomes significant (for flare and nonflare cases), strongly overlapping with a flare related NO feature in Earth's atmosphere.

Previous continuum observations from the MUSTANG camera on the Green Bank Telescope (GBT) of the nearby star-forming filament OMC 2/3 found elevated emission at 3.3 mm relative to shorter-wavelength data. As a consequence, the inferred dust emissivity index obtained from modified blackbody dust spectra was considerably lower than what is typically measured on ∼0.1 pc scales in nearby molecular clouds. Here we present new observations of OMC 2/3 collected with the MUSTANG-2 camera on the GBT that confirm this elevated emission. We also present for the first time sensitive 1 cm observations made with the Ka-band receiver on the GBT, which also show higher than expected emission. We use these observations—along with Herschel, JCMT, Mambo, and GISMO data—to assemble spectral energy distributions (SEDs) of a variety of structures in OMC 2/3 spanning the range 160 μm to 1 cm. The data at 2 mm and shorter are generally consistent with a modified blackbody spectrum and a single value of β ∼ 1.6. The 3 mm and 1 cm data, however, lie well above such an SED. The spectrum of the long-wavelength excess is inconsistent with both free–free emission and standard "Spinning Dust" models for Anomalous Microwave Emission (AME). The 3 mm and 1 cm data could be explained by a flatter dust emissivity at wavelengths shorter than 2 mm, potentially in concert with AME in some regions.

High-redshift quasars typically have their redshift determined from rest-frame ultraviolet (UV) emission lines. However, these lines, and more specifically the prominent C ivλ1549 emission line, are typically blueshifted yielding highly uncertain redshift estimates compared to redshifts determined from rest-frame optical emission lines. We present near-infrared spectroscopy of 18 luminous quasars at 2.15 < z < 3.70 that allows us to obtain reliable systemic redshifts for these sources. Together with near-infrared spectroscopy of an archival sample of 44 quasars with comparable luminosities and redshifts, we provide prescriptions for correcting UV-based redshifts. Our prescriptions reduce velocity offsets with respect to the systemic redshifts by ∼140 km s⁻¹ and reduce the uncertainty on the UV-based redshift by ∼25% with respect to the best method currently used for determining such values. We also find that the redshifts determined from the Sloan Digital Sky Survey Pipeline for our sources suffer from significant uncertainties, which cannot be easily mitigated. We discuss the potential of our prescriptions to improve UV-based redshift corrections given a much larger sample of high-redshift quasars with near-infrared spectra.

Strong gravitational lensing is a promising probe of the substructure of dark matter halos. Deep-learning methods have the potential to accurately identify images containing substructure, and differentiate weakly interacting massive particle dark matter from other well motivated models, including vortex substructure of dark matter condensates and superfluids. This is crucial in future efforts to identify the true nature of dark matter. We implement, for the first time, a classification approach to identifying dark matter based on simulated strong lensing images with different substructure. Utilizing convolutional neural networks trained on sets of simulated images, we demonstrate the feasibility of deep neural networks to reliably distinguish among different types of dark matter substructure. With thousands of strong lensing images anticipated with the coming launch of Vera C. Rubin Observatory, we expect that supervised and unsupervised deep-learning models will play a crucial role in determining the nature of dark matter.

Cosmic rays, along with stellar radiation and magnetic fields, are known to make up a significant fraction of the energy density of galaxies such as the Milky Way. When cosmic rays interact in the interstellar medium, they produce gamma-ray emission which provides an important indication of how the cosmic rays propagate. Gamma-rays from the Andromeda galaxy (M31), located 785 kpc away, provide a unique opportunity to study cosmic-ray acceleration and diffusion in a galaxy with a structure and evolution very similar to the Milky Way. Using 33 months of data from the High Altitude Water Cherenkov Observatory, we search for teraelectronvolt gamma-rays from the galactic plane of M31. We also investigate past and present evidence of galactic activity in M31 by searching for Fermi bubble-like structures above and below the galactic nucleus. No significant gamma-ray emission is observed, so we use the null result to compute upper limits on the energy density of cosmic rays >10 TeV in M31.

Recent studies have revealed that the onset age for the presence of multiple stellar populations (MPs) in star clusters seems to correspond to the disappearance of the extended main-sequence turnoff in young clusters, a pattern associated with stellar rotations. A speculative suggestion is that MPs might be caused by the magnetic brake, a stellar evolutionary effect linked to rotation. In this work, we use the young massive cluster NGC 419 as a testbed. We examined if its magnetically baked MS stars would exhibit MPs. Using the deep ultraviolet and visible images observed through the Hubble Space Telescope, combined with a specific color index that is sensitive to the nitrogen (N) abundance, we examined if its late G- and K-type MS stars are affected by N variation. Our analysis reports that the morphology of its GK-type MS is most likely a simple stellar population, and only a negligible probability, which indicates a N variation up to 0.4 dex is present. We therefore conclude that there is no significant N variation among its GK-type MS stars. The absence of a significant chemical variation among the late-type MS stars indicates that MPs might not be a specific pattern of magnetically braked stars.

The cosmic microwave background (CMB) monopole temperature evolves with the inverse of the cosmological scale factor, independent of many cosmological assumptions. With sufficient sensitivity, real-time cosmological observations could thus be used to measure the local expansion rate of the universe using the cooling of the CMB. We forecast how well a CMB spectrometer could determine the Hubble constant via this method. The primary challenge of such a mission lies in the separation of Galactic and extra-Galactic foreground signals from the CMB at extremely high precision. However, overcoming these obstacles could potentially provide an independent, highly robust method to shed light on the current low-/high-z Hubble tension. An experiment with 3000 linearly spaced bins between 5 GHz and 3 THz with a sensitivity of 1 $\mathrm{mJy}\sqrt{\mathrm{yr}}\,{\mathrm{sr}}^{-1}$ per bin, could measure H₀ to 3% over a 10 yr mission, given current foreground complexity. This sensitivity would also enable high-precision measurements of the expected ΛCDM spectral distortions, but remains futuristic at this stage.

Bars in disk-dominated galaxies are able to drive gas inflow inside the corotation radius, thus enhancing the central star formation rate (SFR). Previous work, however, has found that disk-dominated galaxies with centrally suppressed SFRs frequently host a bar. Here we investigate possible causes for the suppression of central SFRs in such cases. We compare the physical properties of a sample of disk-dominated barred galaxies with high central SFRs (HC galaxies) with those of a sample of disk-dominated barred galaxies with low central SFRs (LC galaxies). We find that the two samples have, on average, similar H i content and bars of similar strength. But we also find that the HCs have bluer colors than the LCs, and that outside the bar region, they host stronger spiral arms than the LCs, where closed rings are more often seen. We discuss and evaluate the possible causes for the suppression of the central SFR in the LC galaxies as opposed to its enhancement in the HC galaxies.

I show that a flow structure where wide jets hit a slower expanding shell might be very efficient in channeling the kinetic energy of the jets to radiation, therefore accounting for, at least a fraction of, intermediate-luminosity optical transients (ILOTs) where the total radiation energy is much larger than what recombination energy of the outflow can supply. This type of flow might occur in the frame of the high-accretion-powered ILOT (HAPI) model, where there is a high mass accretion rate as a result of stellar merger or mass transfer in a binary system. I derive the condition on the jets half opening angle for the jets not to penetrate through the slow shell, as well as the ratio of the photon diffusion time to expansion time. This ratio cannot be too large if a large fraction of the thermal energy is channeled to radiation. I apply the jet-powered radiation model to the Great Eruption of Eta Carinae, to V838 Mon, and to V4332 Sgr, and find a plausible set of parameters for these ILOTs. I expect the jet-powered radiation model to be more efficient in converting kinetic energy to radiation than ILOT models that are based on equatorial mass concentration. In many cases, though, I expect both jets and equatorial mass concentration to occur in the same system.

The density profiles of dwarf galaxies are a highly varied set. If the dark matter is an ultra-light particle such as axions, then simulations predict a distinctive and unique profile. If the axion mass is large enough to fit the ultra-faint dwarf (UFD) satellites ($m\gtrapprox {10}^{-21}$ eV), then the models do not fit the density profile of Fornax and Sculptor and are ruled out by more than $3-\sigma$ confidence. If the axion mass is in the mass range that can fit mass profiles of Fornax and Sculptor dwarf spheroidals, then its extended profile implies enormous masses ($\approx {10}^{11}\mbox{--}{10}^{12}\,{M}_{\odot }$) for the UFDs. These large masses for the UFDS are ruled out by more than $3-\sigma$ confidence by dynamical friction arguments. The tension would increase further considering star formation histories and stellar masses of the UFDs. Unless future ultra-light dark matter (ULDM) simulations with baryonic feedback show a significant change in the density structure of the halos, the current data is incompatible with the ULDM scenario. Relaxing the slope constraint from classical dwarf galaxies would lead to excluding ULDM with mass less than $6\times {10}^{-22}\,{\rm{eV}}$.

An analysis of model fit results of 15,210 electron velocity distribution functions (VDFs), observed within ±2 hr of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 au, is presented as the third and final part on electron VDFs near IP shocks. The core electrons and protons dominate in the magnitude and change in the partial-to-total thermal pressure ratio, with the core electrons often gaining as much or more than the protons. Only a moderate positive correlation is observed between the electron temperature and the kinetic energy change across the shock, while weaker, if any, correlations were found with any other macroscopic shock parameter. No VDF parameter correlated with the shock normal angle. The electron VDF evolves from a narrowly peaked core with flaring suprathermal tails in the upstream to either a slightly hotter core with steeper tails or much hotter flattop core with even steeper tails downstream of the weaker and strongest shocks, respectively. Both quasi-static and fluctuating fields are examined as possible mechanisms modifying the VDF, but neither is sufficient alone. For instance, flattop VDFs can be generated by nonlinear ion acoustic wave stochastic acceleration (i.e., inelastic collisions), while other work suggested they result from the combination of quasi-static and fluctuating fields. This three-part study shows that not only are these systems not thermodynamic in nature; even kinetic models may require modification to include things like inelastic collision operators to properly model electron VDF evolution across shocks or in the solar wind.

We use K-band spectroscopic data from the Multi-Object Spectroscopic Emission Line survey to analyze the kinematic properties of galaxies at z > 3. Our sample consists of 34 galaxies at 3.0 < z_spec < 3.8 between 9.0 < $\mathrm{log}({M}_{* }/{M}_{\odot })$ < 11.0. We find that galaxies with $\mathrm{log}({M}_{* }/{M}_{\odot })$ > 10.2 at z > 3 have 56 ± 21 km s⁻¹ lower integrated velocity dispersion compared to galaxies at z ≃ 2 of similar stellar mass. Massive galaxies at z > 3 have either a flat or declining star formation history (SFH), whereas similar stellar mass galaxies at z ∼ 2.0 exhibit a slight peak in the past 500 Myr. Comparing with the IllustrisTNG cosmological simulation, we find that (i) the dynamical mass of massive galaxies in simulations ($\mathrm{log}({M}_{* }/{M}_{\odot })$ > 10.0) increases by ∼0.1 dex at a fixed stellar mass between z = 2.0–3.0, and (ii) dynamical mass growth is coupled with a rapid rise in the ex situ stellar mass fraction (stars accreted from other galaxies) for massive galaxies at z < 3.5. We speculate that the rising contribution of ex situ stellar mass to the total stellar mass growth of massive galaxies is driving the higher integrated velocity dispersion and rising SFHs of massive galaxies at z ∼ 2.0 compared to galaxies of similar stellar masses at z > 3.

We perform an analysis of the line-of-sight (LOS) observables of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) for models of the solar atmosphere heated by precipitating high-energy electrons during solar flares. The radiative hydrodynamic (RADYN) flare models are obtained from the F-CHROMA database. The Stokes profiles for the Fe 6173 Å line observed by SDO/HMI are calculated using the radiative transfer code RH1.5D, assuming statistical equilibrium for atomic level populations, and imposing uniform background vertical magnetic fields of various strengths. The SDO/HMI observing sequence and LOS data processing pipeline algorithm are applied to derive the observables (continuum intensity, line depth, Doppler velocity, LOS magnetic field). Our results reveal that the strongest deviations of the observables from the actual spectroscopic line parameters are found for the model with a total energy deposited of E_total = 1.0 × 10¹² erg cm⁻², injected with a power-law spectral index of δ = 3 above a low-energy cutoff of E_c = 25 keV. The magnitudes of the velocity and magnetic field deviations depend on the imposed magnetic field, and can reach 0.35 km s⁻¹ for LOS velocities, 90 G for LOS magnetic field, and 3% for continuum enhancement for the 1000 G imposed LOS magnetic field setup. For E_total ≥ 3.0 × 10¹¹ erg cm⁻² models, the velocity and magnetic field deviations are most strongly correlated with the energy flux carried by ∼50 keV electrons, and the continuum enhancement is correlated with the synthesized ∼55–60 keV hard X-ray photon flux. The relatively low magnitudes of perturbations of the observables and absence of magnetic field sign reversals suggest that the considered RADYN beam heating models augmented with the uniform vertical magnetic field setups cannot explain the strong transient changes found in the SDO/HMI observations.

Using quasar Mg ii narrow absorption lines (NALs) with velocity offset ($\beta \equiv \tfrac{{\upsilon }_{r}}{c}=\tfrac{{\left(1+{z}_{\mathrm{em}}\right)}^{2}-({1+{z}_{\mathrm{abs}})}^{2}}{{\left(1+{z}_{\mathrm{em}}\right)}^{2}+{\left(1+{z}_{\mathrm{abs}}\right)}^{2}}$, where c is the speed of light) ${\upsilon }_{r}\lt {\rm{10,000}}$$\mathrm{km}\,{{\rm{s}}}^{-1}$, this paper investigates the $[{\rm{O}}\,{\rm{II}}]$ emissions and reddening associated with Mg ii NALs by constructing composite spectra. Dust extinctions of all the inflow (${\upsilon }_{r}\lt -750$$\mathrm{km}\,{{\rm{s}}}^{-1}$), environment (−750 ≤ $\upsilon$_r < 600 $\mathrm{km}\,{{\rm{s}}}^{-1}$), outflow ($600\leqslant {\upsilon }_{r}\lt 2000$$\mathrm{km}\,{{\rm{s}}}^{-1}$), and strong intervening-like (2000 ≤ $\upsilon$_r < 6000 $\mathrm{km}\,{{\rm{s}}}^{-1}$) Mg ii NALs can be described by the SMC extinction curve, which suggest that all four types of Mg ii NALs have similar dust properties. The colors of quasars hosting intervening-like Mg ii NALs with ${W}_{r}^{\lambda \leqslant 1.5}$ Å and intervening Mg ii NALs (${\upsilon }_{r}\geqslant 6000$$\mathrm{km}\,{{\rm{s}}}^{-1}$) are similar to those of control quasars (without Mg ii NALs with ${\upsilon }_{r}\lt {\rm{10,000}}$$\mathrm{km}\,{{\rm{s}}}^{-1}$), which suggests that these two types of Mg ii NALs are mainly formed within media unconnected with background quasars. The other three types of Mg ii NALs have much more obvious reddening to background quasars, and the stronger absorptions or the absorptions detected in radio detected quasars produce larger reddening than the weaker absorptions or the absorptions in radio undetected quasars. In addition, the dust-to-gas ratios within inflow Mg ii NALs are possibly lower than those within environment ones. We find that flux ratios $[{\rm{O}}\,{\rm{II}}]$/$[\mathrm{Ne}\,{\rm{V}}]$ of quasars hosting inflow, outflow, intervening-like, and intervening Mg ii NALs are similar to those of control quasars. For quasars hosting environment Mg ii NALs, (1) the flux ratio $[{\rm{O}}\,{\rm{II}}]$/$[\mathrm{Ne}\,{\rm{V}}]$ is much higher than that of control quasars, which suggests that there is a high star formation rate within the host galaxies of environment Mg ii NALs; (2) the flux ratio $[{\rm{O}}\,{\rm{II}}]$/$[\mathrm{Ne}\,{\rm{V}}]$ is positively correlated with absorption strengths; and (3) radio detected quasars have a slightly higher flux ratio $[{\rm{O}}\,{\rm{II}}]$/$[\mathrm{Ne}\,{\rm{V}}]$ when compared to radio undetected quasars, which suggests that the quasar feedback enhances the star formation rate within host galaxies of environment absorbers. For quasars hosting outflow Mg ii NALs, we find that $[{\rm{O}}\,{\rm{II}}]$ emission lines display excesses at blue wings with respect to the line profiles of control quasars, and the excesses are positively correlated with absorption strengths.

The physics regulating star formation (SF) in Hickson Compact Groups (HCG) has thus far been difficult to describe, due to their unique kinematic properties. In this study, we expand upon previous works to devise a more physically meaningful SF relation able to better encompass the physics of these unique systems. We combine CO(1–0) data from the Combined Array from Research in Millimeter Astronomy to trace the column density of molecular gas ${{\rm{\Sigma }}}_{\mathrm{gas}}$ and deep Hα imaging taken on the Southern Astrophysical Research Telescope tracing ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ to investigate SF efficiency across face-on HCG, NGC 7674. We find a lack of universality in SF, with two distinct sequences present in the ${{\rm{\Sigma }}}_{\mathrm{gas}}$–${{\rm{\Sigma }}}_{\mathrm{SFR}}$ plane; one for inside and one for outside the nucleus. We devise an SF relation based on the multi-freefall nature of gas and the critical density, which itself is dependent on the virial parameter ${\alpha }_{\mathrm{vir}}$, the ratio of turbulent to gravitational energy. We find that our modified SF relation fits the data and describes the physics of this system well with the introduction of a virial parameter of about 5–10 across the galaxy. This ${\alpha }_{\mathrm{vir}}$ leads to an order-of-magnitude reduction in SFR compared to ${\alpha }_{\mathrm{vir}}\approx 1$ systems.

The physical properties of faint stellar and substellar objects often rely on indirect, model-dependent estimates. For example, the masses of brown dwarfs are usually inferred using evolutionary models, which are age dependent and have yet to be properly calibrated. With the goal of identifying new benchmark objects to test low-mass stellar and substellar models, we have carried out a comprehensive adaptive optics survey as part of the TaRgetting bENchmark-objects with the Doppler Spectroscopy high-contrast imaging program. Using legacy radial velocity measurements from the High Resolution Echelle Spectrometer at Keck, we have identified several dozen stars that show long-term Doppler accelerations. We present follow-up high-contrast observations from the campaign and report the discovery of 31 comoving companions, as well as 11 strong candidate companions, to solar-type stars with well-determined parallax and metallicity values. Benchmark objects of this nature lend themselves to orbit determinations, dynamical mass estimates, and independent compositional assessment. This compendium of benchmark objects will serve as a convenient test group to substantiate theoretical evolutionary and atmospheric models near the hydrogen fusing limit.

Measuring the physical parameters of coronal mass ejections (CMEs), particularly their entrained magnetic field, is crucial for understanding their physics and for assessing their geoeffectiveness. At the moment, only remote sensing techniques can probe these quantities in the corona, the region where CMEs form and acquire their defining characteristics. Radio observations offer the most direct means for estimating the magnetic field when gyrosynchrotron emission is detected. In this work we measure various CME plasma parameters, including its magnetic field, by modeling the gyrosynchrotron emission from a CME. The dense spectral coverage over a wide frequency range provided by the Murchison Widefield Array (MWA) affords a much better spectral sampling than possible before. The MWA images also provide a much higher imaging dynamic range, enabling us to image these weak emissions. Hence we are able to detect radio emission from a CME at larger distances (∼4.73 R_⊙) than have been reported before. The flux densities reported here are among the lowest measured in similar works. Our ability to make extensive measurements on a slow and otherwise unremarkable CME suggests that with the availability of data from the new-generation instruments like the MWA, it should now be possible to make routine, direct detections of radio counterparts of CMEs.

In this paper, we build from previous work and present simulations of recent (within the past Gyr), magnetized, cosmic-ray driven outflows from the Large Magellanic Cloud (LMC), including our first attempts to explicitly use the derived star formation history of the LMC to seed outflow generation. We run a parameter set of simulations for different LMC gas masses and cosmic-ray transport treatments, and we make preliminary comparisons to published outflow flux estimates, neutral and ionized hydrogen observations, and Faraday rotation measure maps. We additionally report on the gas mass that becomes unbound from the LMC disk and swept by ram pressure into the Trailing Magellanic Stream. We find that, even for our largest outburst, the mass contribution to the Stream is still quite small, as much of the outflow-turned-halo gas is shielded on the LMCs far-side due to the LMCs primarily face-on infall through the Milky Way halo over the past Gyr. On the LMC's near-side, past outflows have fought an uphill battle against ram pressure, with the near-side halo mass being at least a factor of a few smaller than that of the far-side. Absorption-line studies probing only the LMC foreground, then, may be severely underestimating the total mass of the LMC halo formed by outflows.

We present results from the Nuclear Spectroscopic Telescope Array observations of the new black hole X-ray binary candidate MAXI J1631–479 at two epochs during its 2018–2019 outburst, which caught the source in a disk dominant state and a power-law dominant state. Strong relativistic disk reflection features are clearly detected, displaying significant variations in the shape and strength of the broad iron emission line between the two states. Spectral modeling of the reflection spectra reveals that the inner radius of the optically thick accretion disk evolves from <1.9 ${r}_{{\rm{g}}}$ to 12 ± 1 r_g (statistical errors at 90% confidence level) from the disk dominant to the power-law dominant state. Assuming in the former case that the inner disk radius is consistent with being at the innermost stable circular orbit, we estimate a black hole spin of a* > 0.94. Given that the bolometric luminosity is similar in the two states, our results indicate that the disk truncation observed in MAXI J1631–479 in the power-law dominant state is unlikely to be driven by a global variation in the accretion rate. We propose that it may instead arise from local instabilities in the inner edge of the accretion disk at high accretion rates. In addition, we find an absorption feature in the spectra centered at 7.33 ± 0.03 keV during the disk dominant state, which is evidence for the rare case that an extremely fast disk wind (${v}_{\mathrm{out}}={0.067}_{-0.004}^{+0.001}\,c$) is observed in a low-inclination black hole binary, with the viewing angle of 29° ± 1° as determined by the reflection modeling.

The Galactic Center black hole (Sgr A*) provides an ideal laboratory for astronomical tests of new gravitational physics. This work reports that curvature correction (f(R)) to quantum vacuum fluctuations naturally yields a Yukawa-type scalar fifth force with potential $\exp \left(-{M}_{\psi }r\right)/r$, where M_ψ is the mass of the f(R) scalarons. Estimating the UV and IR cutoff scales of vacuum fluctuations, the Yukawa coupling strength is connected to the scalaron field amplitude. Whereas recently constrained Yukawa coupling and range correspond to light scalarons with M_ψ = (1.37 × 10⁻²¹–5.49 × 10⁻²⁰) eV, vacuum fluctuations yield a massive scalaron with M_ψ = 10⁻¹⁶ eV. Scalaron-induced periastron shift of stellar orbits near Sgr A* has been studied with respect to the semimajor axis in the range a = 10–1000 au. It is found that the scalarons resulting from quantum fluctuations affect the precession of orbits with a = 128–256 R_s. The possibility of future constraints on massive scalarons in observations near Sgr A* is discussed. This is a new and independent effort to express a prototype quantum gravity effect in terms of astronomically accessible quantities.

The presence of a volume-density gradient in molecular clumps allows them to raise their star formation rate compared with what they would experience if their gas were uniform in density. This higher value for the star formation rate yields in turn a higher star formation efficiency per free-fall time that we measure. The measured star formation efficiency per free-fall time, ${\epsilon }_{\mathrm{ff},\mathrm{meas}}$, of clumps is therefore plagued by a degeneracy, as two factors contribute to it: one is the density gradient of the clump gas, the other is the intrinsic star formation efficiency per free-fall time, ${\epsilon }_{\mathrm{ff},\mathrm{int}}$, with which the clump would form stars should there be no gas-density gradient. This paper presents a method allowing one to recover the intrinsic efficiency of a centrally concentrated clump. It hinges on the relation between the surface densities in stars and gas measured locally from clump center to clump edge. Knowledge of the initial density profile of the clump gas is not required. A step-by-step description of the method is provided as a tool in hand for observers. Once ${\epsilon }_{\mathrm{ff},\mathrm{int}}$ has been estimated, it can be compared with its measured, clump-averaged, counterpart, ${\epsilon }_{\mathrm{ff},\mathrm{meas}}$, to quantify the impact that the initial gas-density profile of a clump has had on its star formation history.

The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, has not been thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations (007, 4.2 pc; 348.5 GHz, 860 μm). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of 3.7% ± 0.5% and position angle of 109° ± 2° (B-vector) at ∼8 pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 μm continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from (1) an inhomogeneous optical depth and (2) a variation of the velocity dispersion, i.e., a variation of the magnetic field turbulence at subparsec scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few parsecs contribute to the accretion flow onto the active nuclei.

We perform plasma diagnostics, including that of the non-Maxwellian κ-distributions, in several structures observed in the solar corona by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on board the Hinode spacecraft. To prevent uncertainties due to the in-flight calibration of EIS, we selected spectral atlases observed shortly after the launch of the mission. One spectral atlas contains an observation of an active region, while the other is an off-limb quiet-Sun region. To minimize the uncertainties of the diagnostics, we rely only on strong lines and average the signal over a spatial area within selected structures. Multiple plasma parameters are diagnosed, such as the electron density, the differential emission measure, and the non-Maxwellian parameter κ. To do that, we use a simple, well-converging iterative scheme based on refining the initial density estimates via the differential emission measure (DEM) and κ. We find that while the quiet-Sun spectra are consistent with a Maxwellian distribution, the coronal loops and moss observed within the active region are strongly non-Maxwellian with κ ⪅ 3. These results were checked by calculating synthetic ratios using DEMs obtained as a function of κ. Ratios predicted using the DEMs assuming κ-distributions converged to the ratios observed in the quiet Sun and coronal loops. To our knowledge, this work presents a strong evidence of the presence of different electron distributions between two physically distinct parts of the solar corona.

Data from the Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo detectors have confirmed that stellar-mass black holes can merge within a Hubble time, leaving behind massive remnant black holes. In some astrophysical environments such as globular clusters and active galactic nucleus disks, it may be possible for these remnants to take part in further compact-object mergers, producing a population of hierarchically formed black holes. In this work, we present a parameterized framework for describing the population of binary black hole (BBH) mergers, while self-consistently accounting for hierarchical mergers. The framework casts black holes as particles in a box that can collide based on an effective cross section, but allows inputs from more detailed astrophysical simulations. Our approach is relevant to any population that is comprised of second- or higher-generation black holes, such as primordial black holes or dense cluster environments. We describe some possible inputs to this generic model and their effects on the black hole merger populations and use the model to perform Bayesian inference on the catalog of black holes from LIGO and Virgo's first two observing runs. We find that models with a high rate of hierarchical mergers are disfavored, consistent with previous population analyses. Future gravitational-wave events will further constrain the inputs to this generic hierarchical merger model, enabling a deeper look into the formation environments of BBHs.

Understanding the anomalous radii of many transiting hot gas-giant planets is a fundamental problem of planetary science. Recent detections of reinflated warm Jupiters orbiting post-main-sequence stars and the reinflation of hot Jupiters while their host stars evolve on the main sequence may help constrain models for the anomalous radii of hot Jupiters. In this work, we present evolution models studying the reinflation of gas giants to determine how varying the depth and intensity of deposited heating affects both main-sequence reinflation of hot Jupiters and post-main-sequence reinflation of warm Jupiters. We find that deeper heating is required to reinflate hot Jupiters than is needed to suppress their cooling, and that the timescale of reinflation decreases with increasing heating rate and depth. We find a strong degeneracy between heating rate and depth, with either strong shallow heating or weak deep heating providing an explanation for main-sequence reinflation of hot Jupiters. This degeneracy between heating rate and depth can be broken in the case of post-main-sequence reinflation of warm Jupiters, as the inflation must be rapid to occur within post-main-sequence evolution timescales. We also show that the dependence of heating rate on the incident stellar flux inferred from the sample of hot Jupiters can explain reinflation of both warm and hot Jupiters. TESS will obtain a large sample of warm Jupiters orbiting post-main-sequence stars, which will help to constrain the mechanism(s) causing the anomalous radii of gas-giant planets.

The cosmic origin of fluorine is still not well constrained. Several nucleosynthetic channels at different phases of stellar evolution have been suggested, but these must be constrained by observations. For this, the fluorine abundance trend with metallicity spanning a wide range is required. Our aim is to determine stellar abundances of fluorine for $-1.1\lt [\mathrm{Fe}/{\rm{H}}]\lt +0.4$. We determine the abundances from HF lines in infrared K-band spectra ($\sim 2.3\,\mu {\rm{m}}$) of cool giants, observed with the IGRINS and Phoenix high-resolution spectrographs. We derive accurate stellar parameters for all our observed K giants, which is important as the HF lines are very temperature-sensitive. We find that [F/Fe] is flat as a function of metallicity at [F/Fe]∼0, but increases as the metallicity increases. The fluorine slope shows a clear secondary behavior in this metallicity range. We also find that the [F/Ce] ratio is relatively flat for $-0.6\lt [\mathrm{Fe}/{\rm{H}}]\lt 0$, and that for two metal-poor ($[\mathrm{Fe}/{\rm{H}}]\lt -0.8$), s-process element-enhanced giants, we do not detect an elevated fluorine abundance. We interpret all of these observational constraints as indications that several major processes are at play for the cosmic budget of fluorine over time: from those in massive stars at low metallicities, through the asymptotic giant branch star contribution at $-0.6\lt [\mathrm{Fe}/{\rm{H}}]\lt 0$, to processes with increasing yields with metallicity at supersolar metallicities. The origins of the latter, and whether or not Wolf–Rayet stars and/or novae could contribute at supersolar metallicities, is currently not known. To quantify these observational results, theoretical modeling is required. More observations in the metal-poor region are required to clarify the processes there.

Gamma-ray burst (GRB) prompt emission is highly beamed, and understanding the jet geometry and beaming configuration can provide information on the poorly understood central engine and circumburst environment. Prior to the advent of gravitational-wave astronomy, astronomers relied on observations of jet breaks in the multiwavelength afterglow to determine the GRB opening angle, since the observer's viewing angle relative to the system cannot be determined from the electromagnetic data alone. Gravitational-wave observations, however, provide an independent measurement of the viewing angle. We describe a Bayesian method for determining the geometry of short GRBs (sGRBs) using coincident electromagnetic and gravitational-wave observations. We demonstrate how an ensemble of multimessenger detections can be used to measure the distributions of the jet energy, opening angle, Lorentz factor, and angular profile of sGRBs; we find that for a population of 100 such observations, we can constrain the mean of the opening angle distribution to within 10° regardless of the angular emission profile. Conversely, the constraint on the energy distribution depends on the shape of the profile, which can be distinguished.

The reason for the difference between the composite X-ray spectrum for radio-loud quasars (RLQs) versus radio-quiet quasars (RQQs) is still unclear. To study this difference, we built a new composite X-ray spectrum of RLQs using Chandra X-ray data and Sloan Digital Sky Survey optical data for the sample of 3CRR quasars. We find the X-ray spectra of all 3CRR quasars, except for 3C 351, have no soft X-ray excess and can be fitted well with an absorbed power-law model. Our composite X-ray spectrum is similar to that of Shang et al. for RLQs, showing higher hard X-ray and lower soft X-ray flux than the composite X-ray spectrum of RQQs. Most blazar-like 3CRR quasars have higher X-ray flux than the median composite X-ray spectrum, which could be related to the contribution of beamed jet emission at X-ray band. From the literature, we find that nineteen 3CRR quasars have extended X-ray emission related to radio jets, indicating the inevitable contribution of jets at X-ray band. In contrast to RQQs, the X-ray photon index of 3CRR quasars does not correlate with the Eddington ratio. Our results suggest that the jet emission at X-ray band in RLQs could be related to the difference in composite X-ray spectrum between RLQs and RQQs.

The current study presents an investigation of the behavior of prominences during eruptions. Variations in the distribution of their velocities are detected at altitudes <0.6 R_⊙. Detailed analyses are carried out for 304 Å Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. To track the behavior of prominences during eruptions, 41 events in the period 2010–2017 are studied. To follow the rise of a filament on higher altitudes (up to 32 R_⊙), Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO) data are also inspected. They are used to obtain kinematic profiles of eruptions. Obtained height–time and speed–time plots of the eruptions show velocity fluctuations in 83% of the explored cases, detected only in the SDO/AIA field of view, and not in any of the prominences observed at higher altitudes by SOHO/LASCO. Time intervals between fluctuations and heights at which they are detected are estimated. Strong periodicity cannot be determined.

A comprehensively theoretical analysis of the broadband spectral energy distributions (SEDs) of large-scale jet knots in 3C 273 is presented to reveal their X-ray radiation mechanism. We show that these SEDs cannot be explained with a single-electron population model when the Doppler boosting effect is either considered or not. By adding a more energetic electron (the leptonic model) or proton (the hadronic model) population, the SEDs of all knots are well represented. In the leptonic model, the electron population that contributes the X-ray emission is more energetic than the one responsible for the radio-optical emission by almost two orders of magnitude; the derived equipartition magnetic field strengths (B_eq) are ∼0.1 mG. In the hadronic model, protons with energy ∼20 PeV are required to interpret the observed X-rays; the B_eq values are several mG, larger than those in the leptonic model. Based on the fact that no resolved substructures are observed in these knots and the fast cooling time of the high-energy electrons does not easily explain the observed X-ray morphologies, we argue that the two distinct electron populations accelerated in these knots are unreasonable and their X-ray emission is attributed to the proton synchrotron radiation accelerated in these knots. In cases where these knots have relativistic motion toward the observer, the super-Eddington issue of the hadronic model can be avoided. Multiwavelength polarimetry and γ-ray observations with high resolution may be helpful to discriminate these models.

We present results from NuSTAR and XMM-Newton observations of the new black hole X-ray binary MAXI J1820+070 at low accretion rates (below 1% of the Eddington luminosity). We detect a narrow Fe Kα emission line, in contrast to the broad and asymmetric Fe Kα line profiles commonly present in black hole binaries at high accretion rates. The narrow line, with weak relativistic broadening, indicates that the Fe Kα line is produced at a large disk radius. Fitting with disk reflection models assuming standard disk emissivity finds a large disk truncation radius (a few tens to a few hundreds of gravitational radii, depending on the disk inclination). In addition, we detect a quasi-periodic oscillation (QPO) varying in frequency between 11.6 ± 0.2 mHz and 2.8 ± 0.1 mHz. The very low QPO frequencies suggest a large size for the optically thin Comptonization region according to the Lense–Thirring precession model, supporting that the accretion disk recedes from the innermost stable circular orbit and is replaced by advection-dominated accretion flow at low accretion rates. We also discuss the possibility of an alternative accretion geometry that the narrow Fe Kα line is produced by a lamppost corona with a large height illuminating the disk.

Recent exoplanet observations reported a large number of multiple-planet systems, in which some of the planets are in a chain of resonances. The fraction of resonant systems to non-resonant systems provides clues about their formation history. We investigated the orbital stability of planets in resonant chains by considering the long-term evolution of planetary mass and stellar mass and using orbital calculations. We found that while resonant chains were stable, they can be destabilized by a change of ∼10% in planetary mass. Such a mass evolution can occur by atmospheric escape due to photoevaporation. We also found that resonant chains can be broken by a stellar mass loss of ≲1%, which would be explained by stellar winds or coronal mass ejections. The long-term mass change of planets and stars plays an important role in the orbital evolutions of planetary systems, including super-Earths.

Fast radio bursts (FRBs) are extragalactic, bright pulses of emission at radio frequencies with millisecond durations. Observationally, FRBs can be divided into two classes, repeating FRBs and non-repeating FRBs. At present, 20 repeating FRBs have been discovered with unknown physical origins. Localization of the first repeating FRB 121102 and discovery of an associated persistent radio source support that FRBs are powered by young millisecond magnetars, which could be formed by the core-collapses of massive stars or binary neutron star (BNS) mergers. These two formation channels can be distinguished by the gravitational waves generated by BNSs mergers. We first calculate the lower limit of the local formation rate of repeating FRBs observed by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Then we show that only a small fraction (6%) of repeating FRBs are produced by young magnetars from BNS mergers, based on the gravitational-wave detections by the third observing run (O3) of the Advanced LIGO/Virgo gravitational-wave detectors. Therefore, we believe that repeating FRBs are more likely produced by newborn magnetars newborn from the core-collapses of massive stars rather than magnetars from BNS mergers.

The intergalactic medium (IGM) at z ∼  5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with $-26\lesssim {M}_{1450}\lesssim -23$, but their number density is poorly constrained at z ∼ 5. In this paper, we present our survey of faint quasars at z ∼ 5 in the European Large-Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg² and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find z ∼ 5 quasars through a two-step approach using the broadband color selection, and spectral energy distribution fitting with the medium-band information included. Adopting Bayesian information criterion, we identify 10 promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at z ∼ 5 and supporting the reliability of the quasar selection. Using the promising candidates, we derive the z ∼ 5 quasar luminosity function at −26 ≲ M₁₄₅₀ ≲ −23. The number density of faint z ∼ 5 quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at z ∼ 5.

We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi's Gamma-ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering the 10 year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events, 2356 of which we identified as cosmic GRBs. Additional trigger events were due to solar flare events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to the community on the most important observables of the GBM-detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50–300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10–1000 keV, exploiting the full energy range of GBM's low-energy detectors. Furthermore, information is given on the settings of the triggering criteria and exceptional operational conditions during years 7 to 10 in the mission. This fourth catalog is an official product of the Fermi-GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

We report the results of a systematic search for ultra-faint Milky Way satellite galaxies using data from the Dark Energy Survey (DES) and Pan-STARRS1 (PS1). Together, DES and PS1 provide multi-band photometry in optical/near-infrared wavelengths over ∼80% of the sky. Our search for satellite galaxies targets ∼25,000 deg² of the high-Galactic-latitude sky reaching a 10σ point-source depth of ≳22.5 mag in the g and r bands. While satellite galaxy searches have been performed independently on DES and PS1 before, this is the first time that a self-consistent search is performed across both data sets. We do not detect any new high-significance satellite galaxy candidates, recovering the majority of satellites previously detected in surveys of comparable depth. We characterize the sensitivity of our search using a large set of simulated satellites injected into the survey data. We use these simulations to derive both analytic and machine-learning models that accurately predict the detectability of Milky Way satellites as a function of their distance, size, luminosity, and location on the sky. To demonstrate the utility of this observational selection function, we calculate the luminosity function of Milky Way satellite galaxies, assuming that the known population of satellite galaxies is representative of the underlying distribution. We provide access to our observational selection function to facilitate comparisons with cosmological models of galaxy formation and evolution.

The population of Milky Way (MW) satellites contains the faintest known galaxies and thus provides essential insight into galaxy formation and dark matter microphysics. Here we combine a model of the galaxy–halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high Galactic latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated 6 ± 2 observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper-motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last 2 Gyr at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below $3.2\times {10}^{8}\ {M}_{\odot }$ at 95% confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. We predict that the faintest detectable satellites occupy halos with peak virial masses above ${10}^{6}\ {M}_{\odot }$, highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.

We report the detection of the Mn-Kα line in the SN-IIb remnant, Cassiopeia A. Manganese (⁵⁵Mn after decay of ⁵⁵Co), a neutron-rich element, together with chromium (⁵²Cr after decay of ⁵²Fe), is mainly synthesized in core-collapse supernovae at the explosive incomplete Si-burning regime. Therefore, the Mn/Cr mass ratio with its neutron excess reflects the neutronization at the relevant burning layer during the explosion. Chandra's deep archival X-ray data of Cassiopeia A indicate a low Mn/Cr mass ratio with values in the range 0.10–0.66, which, when compared to one-dimensional SN explosion models, requires that the electron fraction be 0.4990 ≲ Y_e ≲ 0.5 at the incomplete Si-burning layer. An explosion model assuming a solar-metallicity progenitor with a typical explosion energy (1 × 10⁵¹ erg) fails to reproduce such a high electron fraction. We can satisfy the observed Mn/Cr mass ratio if the explosive Si-burning regime was to extend into the O/Ne hydrostatic layer, which has a higher Y_e. This would require an energetic (>2 × 10⁵¹ erg) and/or asymmetric explosion of a subsolar-metallicity progenitor (Z ≲ 0.5Z_⊙) for Cassiopeia A. The low initial metallicity can be used to rule out a single-star progenitor, leaving the possibility of a binary progenitor with a compact companion. We discuss the detectability of X-rays from Bondi accretion onto such a compact companion around the explosion site. We also discuss other possible mass-loss scenarios for the progenitor system of Cassiopeia A.

We perform two-dimensional and three-dimensional simulations of cold, dense clouds, which are accelerated by radiation pressure on dust relative to a hot, diffuse background gas. We examine the relative effectiveness of acceleration by ultraviolet (UV) and infrared (IR) radiation fields, both independently and acting simultaneously on the same cloud. We study clouds that are optically thin to IR emission but with varying UV optical depths. Consistent with previous work, we find relatively efficient acceleration and long cloud survival times when the IR band flux dominates over the UV flux. However, when the UV flux is dominant or even a modest percentage (∼5%–10%) of the IR irradiating flux, it can act to compress the cloud, first crushing it and then disrupting the outer layers. This drives mixing of the outer regions of the dusty gas with the hot diffuse background to the point where most dust is not likely to survive or stay coupled to the gas. Hence, the cold cloud is unable to survive for a long enough timescale to experience significant acceleration before disruption even though efficient IR cooling keeps the majority of the gas close to the radiative equilibrium temperature (T ≲ 100 K). We discuss the implications for observed systems, concluding that radiation pressure driving is most effective when the light from star-forming regions is efficiently reprocessed into the IR.

We have observed the Class I protostar L1489 IRS with the Atacama Millimeter/submillimeter Array (ALMA) in Band 6. The C¹⁸O J = 2–1 line emission shows flattened and non-axisymmetric structures in the same direction as its velocity gradient due to rotation. We discovered that the C¹⁸O emission shows dips at a radius of ∼200–300 au while the 1.3 mm continuum emission extends smoothly up to r ∼ 400 au. At the radius of the C¹⁸O dips, the rotational axis of the outer portion appears to be tilted by ∼15° from that of the inner component. Both the inner and outer components with respect to the C¹⁸O dips exhibit the r^−0.5 Keplerian rotation profiles until r ∼ 600 au. These results not only indicate that a Keplerian disk extends up to ∼600 au but also that the disk is warped. We constructed a three-dimensional warped-disk model rotating at the Keplerian velocity, and demonstrated that the warped-disk model reproduces main observed features in the velocity channel maps and the PV diagrams. Such a warped-disk system can form by mass accretion from a misaligned envelope. We also discuss a possible disk evolution scenario based on comparisons of disk radii and masses between Class I and Class II sources.

We have obtained a very deep exposure (813 ks) of ζ Puppis (O4 supergiant) with the Chandra HETG Spectrometer. Here we report on analysis of the 1–9 Å region, especially well suited for Chandra, which has a significant contribution from continuum emission between well separated emission lines from high-ionization species. These data allow us to study the hottest plasma present through the continuum shape and emission line strengths. Assuming a power-law emission measure distribution that has a high-temperature cutoff, we find that the emission is consistent with a thermal spectrum having a maximum temperature of 12 MK as determined from the corresponding spectral cutoff. This implies an effective wind shock velocity of 900 km s⁻¹, well below the wind terminal speed of 2250 km s⁻¹. For X-ray emission that forms close to the star, the speed and X-ray flux are larger than can be easily reconciled with strictly self-excited line-deshadowing-instability models, suggesting a need for a fraction of the wind to be accelerated extremely rapidly right from the base. This is not so much a dynamical instability as a nonlinear response to changing boundary conditions.

It has been known for nearly 20 yr that the pseudo-phase-space density profile of equilibrium simulated dark matter halos, ρ(r)/σ³(r), is well described by a power law over three decades in radius, even though both the density ρ(r) and the velocity dispersion σ(r) deviate significantly from power laws. The origin of this scale-free behavior is not understood. It could be an inherent property of self-gravitating collisionless systems, or it could be a mere coincidence. To address the question we work with equilibrium halos and, more specifically, the second derivative of the Jeans equation, which, under the assumptions of (i) the Einasto density profile, (ii) the linear velocity anisotropy–density slope relation, and (iii) ρ/σ³ ∝ r^−α, can be transformed from a differential equation to a cubic algebraic equation. Relations (i)–(iii) are all observed in numerical simulations and are well parameterized by a total of four or six model parameters. We do not consider the dynamical evolution of halos; instead, taking advantage of the fact that the algebraic Jeans equation for equilibrium halos puts relations (i)–(iii) on the same footing, we study the (approximate) solutions of this equation in the four- and six-dimensional spaces. We argue that the distribution of best solutions in these parameter spaces is inconsistent with ρ/σ³ ∝ r^−α being a fundamental property of gravitational evolution and conclude that the scale-free nature of this quantity is likely to be a fluke.

We present our observational results of the 0.87 mm polarized dust emission in the Class 0 protostar B335 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) at a 02 (20 au) resolution. We compared our data at 0.87 mm with those at 1.3 mm from the ALMA archive. The observed polarization orientations at the two wavelengths are consistent within the uncertainty, and the polarization percentages are systematically higher at 1.3 mm than 0.87 mm by a factor of ∼1.7, suggesting that the polarized emission originates from magnetically aligned dust grains. We inferred the magnetic field orientations from the observed polarization orientations. We found that the magnetic field changes from ordered and highly pinched to more complicated and asymmetric structures within the inner 100 au scale of B335, and the magnetic field connects to the center along the equatorial plane as well as along the directions that are ∼40°–60° from the equatorial plane. We performed nonideal MHD simulations of collapsing dense cores. We found that similar magnetic field structures appear in our simulations of dense cores with the magnetic field and rotational axis slightly misaligned by 15° but not in those with the aligned magnetic field and rotational axis. Our results suggest that the midplane of the inner envelope within the inner 100 au scale of B335 could be warped because of the misaligned magnetic field and rotational axis, and the magnetic field could be dragged by the warped accretion flows.

We carried out a statistical study on the effects of strong geomagnetic activity on the mesopause over the auroral region from 2002 to 2018. When the auroral electrojet index increased significantly, the energetic electron precipitation from the Medium Energy Proton and Electron Detector was enhanced by several multiples of 10 for the 55°–70° geomagnetic latitude band. The temperatures measured by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument increased immediately in the mesopause region, together with a descent of the mesopause of about 0.5–2 km. Due to the depth that the precipitation can affect, we conclude that the mesopause is mainly influenced by electrons in the energy range 30–100 keV. The maximum temperature increment at 95 km can reach 4 K and the delay of the response can be up to 1 day. In general, we find that the temperatures significantly respond to the electron precipitation at as low as 93 km, within the mesopause region in most of a year.

We present a study of the evolution of the inner few astronomical units of protoplanetary disks around low-mass stars. We consider nearby stellar groups with ages spanning from 1 to 11 Myr, distributed into four age bins. Combining PANSTARSS photometry with spectral types, we derive the reddening consistently for each star, which we use (1) to measure the excess emission above the photosphere with a new indicator of IR excess and (2) to estimate the mass accretion rate ($\dot{M}$) from the equivalent width of the Hα line. Using the observed decay of $\dot{M}$ as a constraint to fix the initial conditions and the viscosity parameter of viscous evolutionary models, we use approximate Bayesian modeling to infer the dust properties that produce the observed decrease of the IR excess with age, in the range between 4.5 and 24 μm. We calculate an extensive grid of irradiated disk models with a two-layered wall to emulate a curved dust inner edge and obtain the vertical structure consistent with the surface density predicted by viscous evolution. We find that the median dust depletion in the disk upper layers is $\epsilon \sim 3\times {10}^{-3}$ at 1.5 Myr, consistent with previous studies, and it decreases to $\epsilon \sim 3\times {10}^{-4}$ by 7.5 Myr. We include photoevaporation in a simple model of the disk evolution and find that a photoevaporative wind mass-loss rate of $\sim 1\mbox{--}3\times {10}^{-9}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ agrees with the decrease of the disk fraction with age reasonably well. The models show the inward evolution of the H₂O and CO snowlines.

Characterizing the large-scale structure and plasma properties of the inner corona is crucial to understanding the source and subsequent expansion of the solar wind and related space weather effects. Here, we apply a new coronal rotational tomography method, along with a method to narrow streamers and refine the density estimate, to COR2A/Solar Terrestrial Relations Observatory observations from a period near solar minimum and maximum, gaining density maps for heights between 4 and 8R_⊙. The coronal structure is highly radial at these heights, and the streamers are very narrow: in some regions, only a few degrees in width. The mean densities of streamers is almost identical between solar minimum and maximum. However, streamers at solar maximum contain around 50% more total mass due to their larger area. By assuming a constant mass flux, and constraints on proton flux measured by Parker Solar Probe (PSP), we estimate an outflow speed within solar minimum streamers of 50–120 kms⁻¹ at 4R_⊙, increasing to 90–250 kms⁻¹ at 8R_⊙. Accelerations of around 6 ms⁻² are found for streamers at a height of 4R_⊙, decreasing with height. The solar maximum slow wind shows a higher acceleration to extended distances compared with solar minimum. To satisfy the solar wind speeds measured by PSP, there must be a mean residual acceleration of around 1–2 ms⁻² between 8 and 40R_⊙. Several aspects of this study strongly suggest that the coronal streamer belt density is highly variable on small scales, and that the tomography can only reveal a local spatial and temporal average.

We present spectroscopy of stars in the immediate vicinity of the dwarf nova (DN) KZ Gem to confirm its identification, which is ambiguous in the literature. Analysis of 73 radial velocities spanning from 2014 to 2019 provides a high-precision orbital period of 0.2224628(2) days (∼5.34 hr) and shows KZ Gem to be a double-lined DN. Time series photometry taken from 2016 to 2018 shows a variable double-hump modulation with a full amplitude of ∼0.3 mag, along with five Gaussian-like transient events lasting ∼30 minutes or more. Using the light-curve code XRBinary and nonlinear fitting code NMfit, we obtain an optimized binary model of the dwarf nova (DN) KZ Gem, from time series photometry, consisting of a Roche-lobe-filling K-type dwarf with a mass transfer rate of (2.7–7.9) × 10⁻¹⁰M_⊙ yr⁻¹ to a large, cool, and thick disk surrounding a white dwarf, in an orbit with an inclination of 516(±14). Two hotspots on the disk are demonstrated to cause the observed variations in the ellipsoidal modulations from the secondary star. This physical model is compatible with the Gaia distance of KZ Gem.

The cross sections and rate coefficients for inelastic processes in low-energy collisions of sulfur atoms and positive ions with hydrogen atoms and negative ions are calculated for the collisional energy range ${10}^{-4}\mbox{--}100\,\mathrm{eV}$ and for the temperature range 1000–10,000 K. Fifty-five covalent states and two ionic ones are considered. The ground ionic state ${{\rm{S}}}^{+}(3{p}^{3}{}^{4}S^\circ )+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ provides only ${}^{4}{{\rm{\Sigma }}}^{-}$ molecular symmetry, while the first-excited ionic state ${{\rm{S}}}^{+}(3{p}^{3}{}^{2}D^\circ )+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ provides three molecular symmetries: ${}^{2}{{\rm{\Sigma }}}^{-}$, ${}^{2}{\rm{\Pi }}$, and ${}^{2}{\rm{\Delta }}$. The study of sulfur–hydrogen collisions is performed by the quantum model methods within the Born–Oppenheimer formalism. The electronic structure of the collisional quasimolecule is calculated by the semiempirical asymptotic method for each considered molecular symmetry. For nuclear dynamic calculations, the multichannel formula in combination with the Landau–Zener model is used. Nuclear dynamics within each considered symmetry is treated separately, and the total rate coefficients for each inelastic process have been summed over all symmetries. The largest values of the rate coefficients (exceeding ${10}^{-8}\,{\mathrm{cm}}^{3}\ {{\rm{s}}}^{-1}$) correspond to the mutual neutralization processes in ${{\rm{S}}}^{+}(3{s}^{2}3{p}^{3}{}^{4}S^\circ )\,+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ (the ground ionic state being the initial state), as well as in ${{\rm{S}}}^{+}(3{p}^{3}{}^{2}D^\circ )+{{\rm{H}}}^{-}(1{s}^{2}{}^{1}S)$ (the first-excited ionic state being the initial state) collisions. At the temperature 6000 K, the rate coefficients with large magnitudes have the values from the ranges $(1.08\mbox{--}4.48)\times {10}^{-8}\,{\mathrm{cm}}^{3}\,{{\rm{s}}}^{-1}$ and $(1.19\mbox{--}5.05)\times {10}^{-8}\,{\mathrm{cm}}^{3}\,{{\rm{s}}}^{-1}$, respectively. The calculated rate coefficients with large and moderate values are important for NLTE stellar atmosphere modeling.

We present very faint dropout galaxies at z ∼ 6−9 with a stellar mass M_⋆ down to ${M}_{\star }\sim {10}^{6}\,{M}_{\odot }$ that are found in deep optical/near-infrared (NIR) images of the full data sets of the Hubble Frontier Fields (HFF) program in conjunction with deep ground-based and Spitzer images and gravitational-lensing magnification effects. We investigate stellar populations of the HFF dropout galaxies with the optical/NIR photometry and BEAGLE models made of self-consistent stellar population synthesis and photoionization models, carefully including strong nebular emission impacting on the photometry. We identify 453 galaxies with ${M}_{\star }\sim {10}^{6}\mbox{--}{10}^{9}\,{M}_{\odot }$. Our best-estimate ${M}_{\star }/{L}_{\mathrm{UV}}$ function is comparable to a model of star formation duration time of 100 Myr that is assumed in Bouwens et al. We derive the galaxy stellar mass functions (GSMFs) at z ∼ 6–9 that agree with those obtained by previous studies at ${M}_{\star }\gtrsim {10}^{8}\,{M}_{\odot }$, and that extend to ${M}_{\star }\sim {10}^{6}\,{M}_{\odot }$. Estimating the stellar mass densities ${\rho }_{\star }$ with the GSMFs, we find a very slow evolution from z ∼ 9 to z ∼ 6–7, which is consistent with the one estimated from star formation rate density measurements. In conjunction with the estimates of the galaxy effective radii R_e on the source plane, we have pinpointed four objects with low stellar masses (${M}_{\star }\leqslant {10}^{7}\,{M}_{\odot }$) and very compact morphologies (${R}_{{\rm{e}}}\leqslant 40$ pc) that are comparable with those of globular clusters (GCs) in the Milky Way today. These objects are candidates of star clusters, some of which may be related to GCs today.

Muons in neutron stars (NSs) play especially important roles in addressing several interesting new physics questions associated with detecting as well as understanding interactions and astrophysical effects of muonphilic dark matter particles. The key model inputs for studying the latter are the total muon mass M_μ, the muon mass fraction M_μ/M_NS over the NS mass M_NS, and the muon radial density profile ρ_μ(r) in NSs of varying masses. We investigate these quantities within a minimum model for the core of NSs consisting of neutrons, protons, electrons, and muons using an explicitly isospin-dependent parametric equation of state (EOS) constrained by available nuclear laboratory experiments and the latest astrophysical observations of NS masses, radii, and tidal deformabilities. We found that the absolutely maximum muon mass M_μ and its mass fraction M_μ/M_NS in the most massive NSs allowed by causality are about 0.025 M_⊙ and 1.1%, respectively. For the most massive NS of mass 2.14 M_⊙ observed so far, they reduce to about 0.020 M_⊙ and 0.9%, respectively. We also study respective effects of individual parameters describing the EOS of high-density neutron-rich nucleonic matter on the muon contents in NSs with varying masses. We found that the most important but uncertain nuclear physics ingredient for determining the muon contents in NSs is the high-density nuclear symmetry energy.

Impulsively excited sausage oscillations of a plasma cylinder with a smooth radial profile of Alfvén speed are analyzed with a numerical solution of the initial-value problem for a partial differential equation of the Klein–Gordon type, describing linear magnetoacoustic oscillations with a fixed axial wavelength and an azimuthal mode number. The range of analyzed ratios of Alfvén speeds outside and inside the cylinder is from 2 to 10. Both trapped and leaky regimes of the oscillations are considered. It is shown that even in the long-wavelength limit, i.e., for axial wavenumbers much smaller than the cutoff values, damping times of higher radial sausage harmonics could be significantly greater than the oscillation periods, i.e., several oscillation cycles could be present in the signal. The quality factors decrease with decfreasing ratios of Alfvén speeds outside and inside the cylinder. Oscillation periods of the second and third radial harmonics remain practically independent of the axial wavelength even when the wavelength is shorter than the radius of the cylinder. The ratios of oscillation periods of fundamental and higher radial and axial harmonics are found to be significantly different, up to a factor of two in the long-wavelength limit. It is concluded that higher radial harmonics could be responsible for the departure of observed sausage oscillation signals from a harmonic shape, especially during the first several cycles of the oscillation. Even in the absence of spatially resolved data, higher axial and radial harmonics can be distinguished from each other by the period ratios.

We have studied the structure and kinematics of the dense molecular gas in the Orion Molecular Cloud 1 (OMC1) region with the N₂H⁺ 3–2 line. The 6' × 9' (∼0.7 × 1.1 pc) region surrounding the Orion Kleinmann–Low (KL) core has been mapped with the Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The combined SMA and SMT image, with a resolution of ∼54 (∼2300 au), reveals multiple filaments with a typical width of 0.02–0.03 pc. On the basis of the non-local thermodynamic equilibrium analysis using the N₂H⁺ 3–2 and 1–0 data, the density and temperature of the filaments are estimated to be ∼10⁷ cm⁻³ and ∼15 K–20 K, respectively. The core fragmentation is observed in three massive filaments, one of which shows the oscillations in the velocity and intensity that could be the signature of core-forming gas motions. The gas kinetic temperature is significantly enhanced in the eastern part of OMC1, likely due to the external heating from the high-mass stars in M42 and M43. In addition, the filaments are colder than their surrounding regions, suggesting shielding from the external heating due to the dense gas in the filaments. The OMC1 region consists of three subregions, i.e., north, west, and south of Orion KL, having different radial velocities with sharp velocity transitions. There is a north-to-south velocity gradient from the western to the southern regions. The observed velocity pattern suggests that dense gas in OMC1 is collapsing globally toward the high-mass star-forming region, Orion Nebula Cluster.

Recent analysis of high-cadence white-light images taken by the Solar-Terrestrial RElations Observatory near solar maximum has revealed that outflowing density structures are released in a ubiquitous manner in the solar wind. The present study investigates whether these density fluctuations could originate from the transient heating of the low corona observed during coronal bright points (CBPs). We assume that part of the intense heating measured during CBPs occurs at the coronal base of open magnetic fields that channel the forming solar wind. We employ the solar wind model MULTI-VP to quantify the plasma compression induced by transient heating and investigate how the induced perturbation propagates to the upper corona. We show that for heating rates with statistics comparable to those observed during CBPs, the compressive wave initially increases the local plasma density by a factor of up to 50% at 5 R_⊙. The wave expands rapidly beyond 30 solar radii and the local enhancement in density decreases beyond. Based on the occurrence rates of CBPs measured in previous studies, we impose transient heating events at the base of thousands of open magnetic field lines to study the response of the entire 3D corona. The simulated density cubes are then converted into synthetic white-light imagery. We show that the resulting brightness variations occupy all position angles in the images on timescales of hours. We conclude that a significant part of the ubiquitous brightness variability of the solar corona could originate in the strong transient heating of flux tubes induced by CBPs.

We search for microlensing events in the zero-latitude area of the Galactic Bulge using the VVV Survey near-IR data. We have discovered a total sample of N = 630 events within an area covering 20.68 deg² between the years 2010 and 2015. In this paper, we describe the search and present the data for the final sample, including near-IR magnitudes, colors, and proper motions, as well as the standard microlensing parameters. We use the near-IR color–magnitude and color–color diagrams to select N_RC = 290 events with red-clump sources to analyze the extinction properties of the sample in the central region of the Galactic plane. The timescale distribution and its dependence in the longitude axis is presented. The mean timescale decreases as we approach the Galactic minor axis (b = 0°). Finally, we give examples of special microlensing events, such as binaries, short-timescale events, and events with a strong parallax effect.

A scenario for achieving a low velocity dispersion for the galaxy [KKS 2000]04 (aka NGC 1052-DF2) and similar galaxies is presented. A progenitor halo corresponding to a z = 0 halo of mass $\lesssim 5\times {10}^{10}\,{M}_{\odot }$ and a low concentration parameter (but consistent with cosmological simulations) infalls onto a Milky Way–size host at early times. Substantial removal of cold gas from the inner regions by supernova feedback and ram pressure, assisted by tidal stripping of the dark matter in the outer regions, leads to a substantial reduction of the velocity dispersion of stars within one effective radius. In this framework, the observed stellar content of [KKS 2000]04 is associated with a progenitor mass close to that inferred from the global stellar-to-halo-mass ratio. As far as the implications of kinematics are concerned, even if at a ∼20 Mpc distance, it is argued that [KKS 2000]04 is no more peculiar than numerous early type galaxies with seemingly little total dark-matter content.

We investigate starspot distributions consistent with space-based photometry of F, G, and K stars in six stellar associations ranging in age from 10 Myr to 4 Gyr. We show that a simple light-curve statistic called the "smoothed amplitude" is proportional to stellar age as t^−1/2, following a Skumanich-like spin-down relation. We marginalize over the unknown stellar inclinations by forward modeling the ensemble of light curves for direct comparison with the Kepler, K2, and TESS photometry. We sample the posterior distributions for spot coverage with approximate Bayesian computation. We find typical spot coverages in the range 1%–10%, which decrease with increasing stellar age. The spot coverage is proportional to tⁿ where n = −0.37 ± 0.16, also statistically consistent with a Skumanich-like t^−1/2 decay of starspot coverage with age. We apply two techniques to estimate the spot coverage of young exoplanet-hosting stars likely to be targeted for transmission spectroscopy with the James Webb Space Telescope, and estimate the bias in exoplanet radius measurements due to varying starspot coverage.

We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on 2015 January 3–4 at a frequency of 22 GHz (wavelength λ = 1.3 cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space–ground baselines up to 70,833 km (5.6 Earth diameters) for both parallel-hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24 μas, the highest for this source to date. This enabled us to estimate the size of the radio core to be <12 × 5 μas and to reveal a complex structure and a significant curvature of the blazar jet in the inner 100 μas, which is an indication that the jet viewing angle lies inside the opening angle of the jet conical outflow. Fairly highly (15%) linearly polarized emission is detected in a jet region 19 μas in size, located 58 μas downstream from the core. The highest brightness temperature in the source frame is estimated to be >2.2 × 10¹³ K for the blazar core. This implies that the inverse-Compton limit must be violated in the rest frame of the source, even for the largest Doppler factor δ ∼ 25 reported for 0716+714.

Investigating the Gunn–Peterson (GP) trough of high-redshift quasars (QSOs) is a powerful way to reveal the cosmic reionization. As one of such attempts, we perform a series of analyses to examine the absorption lines observed with one of the highest-redshift QSOs, PSO J006.1240+39.2219, which we previously discovered at z = 6.62. Using the Subaru telescope, we obtained medium-resolution spectrum with a total exposure time of 7.5 hr. We calculate the Lyα transmission in different redshift bins to determine the near zone radius and the optical depth at 5.6 < z < 6.5. We find a sudden change in the Lyα transmission at 5.75 < z < 5.86, which is consistent with the result from the literature. The near zone radius of the QSO is 5.79 ± 0.09 pMpc, within the scatter of the near zone radii of other QSOs measured in previous studies. We also analyze the dark gap distribution to probe the neutral hydrogen fractions beyond the saturation limit of the GP trough. We extend the measurement of the dark gaps to 5.7 < z < 6.3. We find that the gap widths increase with increasing redshifts, suggesting more neutral universe at higher redshifts. However, these measurements strongly depend on the continuum modeling. As a continuum model-free attempt, we also perform the dark pixel counting analysis to find the upper limit of $\langle {x}_{{\rm{H}}{\rm{I}}}\rangle \sim 0.6$ (0.8) at z < 5.8 (z > 5.8). All three analyses based on this QSO show increasingly neutral hydrogen toward higher redshifts, adding precious measurements up to z ∼ 6.5.

Core-collapse supernovae can condense large masses of dust post-explosion. However, sputtering and grain–grain collisions during the subsequent passage of the dust through the reverse shock can potentially destroy a significant fraction of the newly formed dust before it can reach the interstellar medium. Here we show that in oxygen-rich supernova remnants like Cassiopeia A, the penetration and trapping within silicate grains of the same impinging ions of oxygen, silicon, and magnesium that are responsible for grain surface sputtering can significantly reduce the net loss of grain material. We model conditions representative of dusty clumps (density contrast of χ = 100) passing through the reverse shock in the oxygen-rich Cassiopeia A remnant and find that, compared to cases where the effect is neglected as well as facilitating the formation of grains larger than those that had originally condensed, ion trapping increases the surviving masses of silicate dust by factors of up to two to four, depending on initial grain radii. For higher density contrasts (χ ≳ 180), we find that the effect of gas accretion on the surface of dust grains surpasses ion trapping, and the survival rate increases to ∼55% of the initial dust mass for χ = 256.

Numerical methods are presented that can determine the perpendicular velocity space diffusion coefficient from kinetic simulation results. The methods are applied to hybrid simulation results using particle protons and a massless, quasi-neutralizing electron fluid for a case of quasi-perpendicular turbulence. During the quasi-steady phase of the turbulence, the evolution of the grid-averaged, gyrotropic, and peculiar velocity distribution of protons with velocity components perpendicular to the background magnetic field is found to be adequately described by diffusion. The estimated diffusion coefficient varies with perpendicular proton speed. A relative maximum occurs at a speed of zero. About the thermal speed, the coefficient decreases with increasing speed consistent with a power law with index −3. A relative minimum occurs at larger speeds, and the diffusion coefficient rises among the fastest protons contained in the simulation. The functional form of the diffusion coefficient appears to be the result of two sources. At speeds less than the relative minimum, the diffusion is dominated by turbulence generated fluctuations, while at greater speeds the diffusion arises from the large-scale fluctuations that initiated the turbulent energy cascade. Results are compared with theoretical predictions for the diffusion coefficient and with results presented from a previous simulation. Implications for generating suprathermal protons from quasi-perpendicular turbulence are also discussed.

We discuss the production of multiple astrophysical messengers (neutrinos, cosmic rays, gamma-rays) in the Gamma-Ray Burst (GRB) internal shock scenario, focusing on the impact of the collision dynamics between two shells on the fireball evolution. In addition to the inelastic case, in which plasma shells merge when they collide, we study the Ultra Efficient Shock scenario, in which a fraction of the internal energy is re-converted into kinetic energy and, consequently, the two shells survive and remain in the system. We find that in all cases, a quasi-diffuse neutrino flux from GRBs at the level of 10⁻¹¹–${10}^{-10}\,\mathrm{GeV}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}\,{\mathrm{sr}}^{-1}$ (per flavor) is expected for protons and a baryonic loading of 10, which is potentially within the reach of IceCube-Gen2. The highest impact of the collision model for multi-messenger production is observed for the Ultra Efficient Shock scenario, that promises high conversion efficiencies from kinetic to radiated energy. However, the assumption that the plasma shells separate after a collision and survive as separate shells within the fireball is found to be justified too rarely in a multicollision model that uses hydrodynamical simulations with the PLUTO code for individual shell collisions.

Building on our previous hydrodynamic study of the angular momenta of cloud cores formed during gravitational collapse of star-forming molecular gas in Kuznetsova et al., we now examine core properties assuming ideal magnetohydrodynamics (MHD). Using the same sink-patch implementation for the Athena MHD code, we characterize the statistical properties of cores, including the mass accretion rates, specific angular momenta, and alignments between the magnetic field and the spin axis of the core on the 0.1 pc scale. Our simulations, which reproduce the observed relation between magnetic field strength and gas density, show that magnetic fields can help collimate low-density flows and help seed the locations of filamentary structures. Consistent with our previous purely hydrodynamic simulations, stars (sinks) form within the heterogeneous environments of filaments, such that accretion onto cores is highly episodic leading to short-term variability but no long-term monotonic growth of the specific angular momenta. With statistical characterization of protostellar cores properties and behaviors, we aim to provide a starting point for building more realistic and self-consistent disk formation models, helping to address whether magnetic fields can prevent the development of (large) circumstellar disks in the ideal MHD limit.

The characterization of the Intracluster Medium (ICM) properties of high-redshift galaxy clusters is fundamental to our understanding of large-scale structure formation processes. We present the results of a multiwavelength analysis of the very massive cluster MOO J1142+1527 at a redshift z = 1.2 discovered as part of the Massive and Distant Clusters of WISE Survey. This analysis is based on high angular resolution Chandra X-ray and NIKA2 Sunyaev–Zel'dovich (SZ) data. The cluster thermodynamic radial profiles have been obtained with unprecedented precision at this redshift and up to 0.7R₅₀₀, thanks to the combination of high-resolution X-ray and SZ data. The comparison between the galaxy distribution mapped in infrared by Spitzer and the morphological properties of the ICM derived from the combined analysis of the Chandra and NIKA2 data leads us to the conclusion that the cluster is an ongoing merger. We have estimated a systematic uncertainty on the cluster total mass that characterizes both the impact of the observed deviations from spherical symmetry and of the core dynamics on the mass profile. We further combine the X-ray and SZ data at the pixel level to obtain maps of the temperature and entropy distributions. We find a relatively low-entropy core at the position of the X-ray peak and high-temperature regions located on its south and west sides. This work demonstrates that the addition of spatially resolved SZ observations to low signal-to-noise X-ray data brings a high information gain on the characterization of the evolution of ICM thermodynamic properties at z > 1.

We perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving, to study the generation of solenoidal velocity components and the small-scale magnetic field. We mainly focus on the effects of mean magnetic field (B₀) and the sonic Mach number (M_s). The dependence of solenoidal ratio (i.e., ratio of solenoidal to kinetic energies) and magnetic energy density on M_s in compressively driven turbulence is already established, but that on B₀ is not yet. We also consider two different driving schemes in terms of the correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. Our findings are as follows. First, when we fix the value of B₀, the solenoidal ratio after saturation increases as ${M}_{s}$ increases. A similar trend is observed for generation of magnetic field when B₀ is small. Second, when we fix the value of ${M}_{s}$, HD and MHD simulations result in similar solenoidal ratios when B₀ is not strong (say, M_A ≳ 5, where M_A is Alfvén Mach number). However, the ratio increases when M_A ≲ 5. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of B₀ irrespective of M_s. Third, generation of the solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Finally, when initial conditions are same, the finite-correlated driving always produces more solenoidal velocity and small-scale magnetic field components than the delta-correlated driving. We additionally analyze the vorticity equation to understand why higher ${M}_{s}$ and B₀ yield a larger quantity of the solenoidal velocity component.

We study the solar eruptive event on 2017 September 10 that produced long-lasting >100 MeV γ-ray emission and a ground level enhancement (GLE72). The origin of the high-energy ions producing late-phase gamma-ray emission (LPGRE) is still an open question, but a possible explanation is proton acceleration at coronal shocks produced by coronal mass ejections. We examine a common shock acceleration origin for both the LPGRE and GLE72. The γ-ray emission observed by the Fermi-Large Area Telescope exhibits a weak impulsive phase, consistent with that observed in hard X-and γ-ray line flare emissions, and what appear to be two distinct stages of LPGRE. From a detailed modeling of the shock wave, we derive the 3D distribution and temporal evolution of the shock parameters, and we examine the shock wave magnetic connection with the visible solar disk. The evolution of shock parameters on field lines returning to the visible disk mirrors the two stages of LPGRE. We find good agreement between the time history of >100 MeV γ-rays and one produced by a basic shock acceleration model. The time history of shock parameters magnetically mapped to Earth agrees with the rates observed by the Fort Smith neutron monitor during the first hour of GLE72 if we include a 30% contribution of flare-accelerated protons during the first 10 minutes, having a release time following the time history of nuclear γ-rays. Our analysis provides compelling evidence for a common shock origin for protons producing the LPGRE and most of the particles observed in GLE72.

In order to obtain an overview of gamma-ray bursts (GRBs), we need a full sample. In this paper, we collected 6289 GRBs (from GRB 910421 to GRB 160509A) from the literature, including their prompt emission, afterglow, and host galaxy properties. We hope to use this large sample to reveal the intrinsic properties of GRBs. We have listed all of the data in machine-readable tables, including the properties of the GRBs, correlation coefficients and linear regression results of two arbitrary parameters, and linear regression results of any three parameters. These machine-readable tables could be used as a data reservoir for further studies on the classifications or correlations. One may find some intrinsic properties from these statistical results. With these comprehensive tables, it is possible to find relations between different parameters and to classify the GRBs into different subgroups. Upon completion, they may reveal the nature of GRBs and may be used as tools like pseudo-redshift indicators, standard candles, etc. All of the machine-readable data and statistical results are available.

Transverse waves are sometimes observed in solar helmet streamers, typically after the passage of a coronal mass ejection (CME). The CME-driven shock wave moves the streamer sideways, and a decaying oscillation of the streamer is observed after the CME passage. Previous works generally reported observations of streamer oscillations taken from a single vantage point (typically the Solar and Heliospheric Observatory (SOHO) spacecraft). We conduct a data survey searching for streamer wave events observed by the COR2 coronagraphs on board the STEREO spacecraft. For the first time, we report observations of streamer wave events from multiple vantage points by using the COR2 instrument on both STEREO A and B, as well as the SOHO/LASCO C2+C3 coronagraphs. We investigate the properties of streamer waves by comparing the different events and performing a statistical analysis. Common observational features give us additional insight on the physical nature of streamer wave events. The most important conclusion is that there appears to be no relation between the speed of the CME and the phase speed of the resulting streamer wave, indicating that the streamer wave speed is determined by the physical properties of the streamer rather than the properties of the CME. This result makes streamer wave events excellent candidates for coronal seismology studies. From a comparison between the measured phase speeds and the phase speeds calculated from the measured periods and wavelengths, we could determine that the speed of the postshock solar wind flow in our streamers is around 300 km s⁻¹.

We present an unbiased spectroscopic study of the Galactic supernova remnant (SNR) Cygnus Loop using the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) DR5. LAMOST features both a large field of view and a large aperture, which allow us to simultaneously obtain 4000 spectra at ∼3700–9000 Å with R ≈ 1800. The Cygnus Loop is a prototype of middle-aged SNRs, which has the advantages of being bright, large in angular size, and relatively unobscured by dust. Along the line of sight to the Cygnus Loop, 2747 LAMOST DR5 spectra are found in total, which are spatially distributed over the entire remnant. This spectral sample is free of the selection bias of most previous studies, which often focus on bright filaments or regions bright in [O iii]. Visual inspection verifies that 368 spectra (13% of the total) show clear spectral features to confirm their association with the remnant. In addition, 176 spectra with line emission show ambiguity of their origin but have a possible association to the SNR. In particular, the 154 spectra dominated by the SNR emission are further analyzed by identifying emission lines and measuring their intensities. We examine distributions of physical properties such as electron density and temperature, which vary significantly inside the remnant, using theoretical models. By combining a large number of the LAMOST spectra, a global spectrum representing the Cygnus Loop is constructed, which presents characteristics of radiative shocks. Finally, we discuss the effect of the unbiased spectral sample on the global spectrum and its implication to understand a spatially unresolved SNR in a distant galaxy.

We explore the kinematics of the stars, ionized gas, and warm molecular gas in the Seyfert 2 galaxy Mrk 3 (UGC 3426) on nuclear and galactic scales with Gemini Near-Infrared Field Spectrograph observations, previous Hubble Space Telescope data, and new long-slit spectra from the Apache Point Observatory (APO) 3.5 m telescope. The APO spectra are consistent with our previous suggestion that a galactic-scale gas/dust disk at P.A. = 129°, offset from the major axis of the host S0 galaxy at P.A. = 28°, is responsible for the orientation of the extended narrow-line region. The disk is fed by an H i tidal stream from a gas-rich spiral galaxy (UGC 3422) ∼100 kpc to the NW of Mrk 3 and is ionized by the active galactic nucleus (AGN) to a distance of at least ∼20'' (∼5.4 kpc) from the central supermassive black hole (SMBH). The kinematics within at least 320 pc of the SMBH are dominated by outflows with radial (line-of-sight) velocities up to 1500 km s⁻¹ in the ionized gas and 500 km s⁻¹ in the warm molecular gas, consistent with in situ heating, ionization, and acceleration of ambient gas to produce the narrow-line region outflows. There is a disk of ionized and warm molecular gas within ∼400 pc of the SMBH that has reoriented close to the stellar major axis but is counterrotating, consistent with claims of external fueling of AGNs in S0 galaxies.

We present a novel, relativistic accretion model for accretion onto a Schwarzschild black hole. This consists of a purely hydrodynamical mechanism in which, by breaking spherical symmetry, a radially accreting flow transitions into an inflow-outflow configuration. The spherical symmetry is broken by considering that the accreted material is more concentrated on an equatorial belt, leaving the polar regions relatively under-dense. What we have found is a flux-limited accretion regime in which, for a sufficiently large accretion rate, the incoming material chokes at a gravitational bottleneck and the excess flux is redirected by the density gradient as a bipolar outflow. The threshold value at which the accreting material chokes is of the order of the mass-accretion rate found in the spherically symmetric case studied by Bondi and Michel. We describe the choked accretion mechanism first in terms of a general relativistic, analytic toy model based on the assumption of an ultrarelativistic stiff fluid. We then relax this approximation and, by means of numerical simulations, show that this mechanism can operate also for general polytropic fluids. Interestingly, the qualitative inflow-outflow morphology obtained appears as a generic result of the proposed symmetry break, across analytic and numeric results covering both the Newtonian and relativistic regimes. The qualitative change in the resulting steady-state flow configuration appears even for a very small equatorial-to-polar-density contrast (∼0.1%) in the accretion profile. Finally, we discuss the applicability of this model as a jet-launching mechanism in different astrophysical settings.

We construct a new analytic phenomenological model for the extended circumgalactic material (CGM) of L* galaxies. Our model reproduces the O vii/O viii absorption observations of the Milky Way (MW) and the O vi measurements reported by the COS-Halos and eCGM surveys. The warm/hot gas is in hydrostatic equilibrium in an MW gravitational potential, and we adopt a barotropic equation of state, resulting in a temperature variation as a function of radius. A pressure component with an adiabatic index of $\gamma =4/3$ is included to approximate the effects of a magnetic field and cosmic rays. We introduce a metallicity gradient motivated by the enrichment of the inner CGM by the Galaxy. We then present our fiducial model for the corona, tuned to reproduce the observed O vi–O viii column densities and with a total mass of ${M}_{\mathrm{CGM}}\approx 5.5\times {10}^{10}$${M}_{\odot }$ inside ${r}_{\mathrm{CGM}}\approx 280\,\mathrm{kpc}$. The gas densities in the CGM are low (${n}_{{\rm{H}}}={10}^{-5}\mbox{--}3\times {10}^{-4}$ cm⁻³), and its collisional ionization state is modified by the metagalactic radiation field. We show that for O vi-bearing warm/hot gas with typical observed column densities ${N}_{{\rm{O}}{\rm{VI}}}\sim 3\times {10}^{14}$ cm⁻² at large ($\gtrsim 100$ kpc) impact parameters from the central galaxies, the ratio of the cooling to dynamical times, ${t}_{\mathrm{cool}}$/${t}_{\mathrm{dyn}}$, has a model-independent upper limit of $\lesssim 4$. In our model, ${t}_{\mathrm{cool}}$/${t}_{\mathrm{dyn}}$ at large radii is $\sim 2\mbox{--}3$. We present predictions for a wide range of future observations of the warm/hot CGM, from UV/X-ray absorption and emission spectroscopy to dispersion measure and Sunyaev–Zel'dovich cosmic microwave background measurements. We provide the model outputs in machine-readable data files for easy comparison and analysis.

Recent numerical simulations of rotating stellar convection have suggested the possible existence of retrograde (slow equator, fast poles) or so-called antisolar differential rotation states in slowly rotating stars possessing a large Rossby number. We aim to understand whether such rotational states exist from the onset of convective instability or are the outcome of complex nonlinear interactions in the turbulent convective envelope. To this end, we have made a systematic linear analysis of the critical state of convection in a series of 15 numerical simulations published in Brun et al. We have assessed their degree of supercriticality and most-unstable mode properties, and computed the second-order mean zonal flow response. We find that none of the linear critical cases show a retrograde state at the onset of convection even when their nonlinear counterparts do. We also find that the presence of a stably stratified layer coupled to the convectively unstable upper layer leads to interesting gravity-wave excitation and angular momentum transport. We conclude that retrograde states of differential rotation are probably the outcome of complex mode–mode interactions in the turbulent convection layer and are, as a consequence, likely to exist in real stars.

We present a Hubble Space Telescope Cosmic Origins Spectrograph spectrum of the QSO SDSS J095109.12+330745.8 (${z}_{\mathrm{em}}=0.645$) whose sightline passes through the SMC-like dwarf galaxy UGC 5282 (${M}_{B}=-16.0$, cz = 1577 km s⁻¹), 1.2 kpc in projection from the central H ii region of the galaxy. Damped Lyα (DLA) absorption is detected at the redshift of UGC 5282 with log [N(H i) cm${}^{-2}]={20.89}_{-0.21}^{+0.12}$. Analysis of the accompanying S ii, P ii, and O i metal lines yields a neutral gas metallicity, ${Z}_{{\rm{H}}{\rm{I}}}$, of [S/H] ≃ [P/H] = −0.80 ± 0.24. The metallicity of ionized gas from the central H ii region ${Z}_{{\rm{H}}{\rm{II}}}$ measured from its emission lines is [O/H] = −0.37 ± 0.10, a difference of +0.43 ± 0.26 from ${Z}_{{\rm{H}}{\rm{I}}}$. This difference δ is consistent with that seen toward H ii regions in other star-forming galaxies and supports the idea that ionized gas near star-forming regions shows systematically higher metallicities than exist in the rest of a galaxy's neutral interstellar medium (ISM). The positive values of δ found in UGC 5282 (and the other star-forming galaxies) is likely due to infalling low-metallicity gas from the intergalactic medium that mixes with the galaxy's ISM on kiloparsec scales. This model is also consistent with broad Lyα emission detected at the bottom of the DLA absorption, offset by ∼125 km s⁻¹ from the absorption velocity. Models of galaxy evolution that attempt to replicate population characteristics, such as the mass–metallicity relation, may need to start with a galaxy metallicity represented by ${Z}_{{\rm{H}}{\rm{I}}}$ rather than that measured traditionally from ${Z}_{{\rm{H}}{\rm{II}}}$.

We present a measurement of the gravitational lensing deflection power spectrum reconstructed with two seasons of cosmic microwave background polarization data from the Polarbear experiment. Observations were taken at 150 GHz from 2012 to 2014 and surveyed three patches of sky totaling 30 square degrees. We test the consistency of the lensing spectrum with a cold dark matter cosmology and reject the no-lensing hypothesis at a confidence of 10.9σ, including statistical and systematic uncertainties. We observe a value of A_L = 1.33 ± 0.32 (statistical) ±0.02 (systematic) ±0.07 (foreground) using all polarization lensing estimators, which corresponds to a 24% accurate measurement of the lensing amplitude. Compared to the analysis of the first-year data, we have improved the breadth of both the suite of null tests and the error terms included in the estimation of systematic contamination.