Table of contents

We present the discovery and early evolution of ASASSN-19bt, a tidal disruption event (TDE) discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 115 Mpc and the first TDE to be detected by TESS. As the TDE is located in the TESS Continuous Viewing Zone, our data set includes 30 minute cadence observations starting on 2018 July 25, and we precisely measure that the TDE begins to brighten ∼8.3 days before its discovery. Our data set also includes 18 epochs of Swift UVOT and XRT observations, 2 epochs of XMM-Newton observations, 13 spectroscopic observations, and ground data from the Las Cumbres Observatory telescope network, spanning from 32 days before peak through 37 days after peak. ASASSN-19bt thus has the most detailed pre-peak data set for any TDE. The TESS light curve indicates that the transient began to brighten on 2019 January 21.6 and that for the first 15 days, its rise was consistent with a flux ∝t² power-law model. The optical/UV emission is well fit by a blackbody spectral energy distribution, and ASASSN-19bt exhibits an early spike in its luminosity and temperature roughly 32 rest-frame days before peak and spanning up to 14 days, which has not been seen in other TDEs, possibly because UV observations were not triggered early enough to detect it. It peaked on 2019 March 4.9 at a luminosity of L ≃ 1.3 × 10⁴⁴ erg s⁻¹ and radiated E ≃ 3.2 × 10⁵⁰ erg during the 41 day rise to peak. X-ray observations after peak indicate a softening of the hard X-ray emission prior to peak, reminiscent of the hard/soft states in X-ray binaries.

Active regions are the source of the majority of magnetic flux rope ejections that become coronal mass ejections (CMEs). To identify in advance which active regions will produce an ejection is key for both space weather prediction tools and future science missions such as Solar Orbiter. The aim of this study is to develop a new technique to identify which active regions are more likely to generate magnetic flux rope ejections. The new technique will aim to (i) produce timely space weather warnings and (ii) open the way to a qualified selection of observational targets for space-borne instruments. We use a data-driven nonlinear force-free field (NLFFF) model to describe the 3D evolution of the magnetic field of a set of active regions. We determine a metric to distinguish eruptive from noneruptive active regions based on the Lorentz force. Furthermore, using a subset of the observed magnetograms, we run a series of simulations to test whether the time evolution of the metric can be predicted. The identified metric successfully differentiates active regions observed to produce eruptions from the noneruptive ones in our data sample. A meaningful prediction of the metric can be made between 6 and 16 hr in advance. This initial study presents an interesting first step in the prediction of CME onset using only line-of-sight magnetogram observations combined with NLFFF modeling. Future studies will address how to generalize the model such that it can be used in a more operational sense and for a variety of simulation approaches.

We explore the possibility of detecting the first galaxies with the next generation of space-based far-infrared (FIR) telescopes by applying an analytical model of primordial dust emission. Our results indicate that FIR/submillimeter sources at z ≳ 7 will experience a strong negative K-correction. Systems of a given virial mass would exhibit larger dust luminosities at higher z, as a consequence of the increase in dust temperature driven by the higher temperature floor set by the cosmic microwave background. In addition, high-z systems are more concentrated, which enhances the heating efficiency associated with stellar radiation. By analyzing source densities as a function of z, and considering survey areas of 0.1 and 10 deg², we find that the redshift horizon for detecting at least one source would be above z ∼ 7 for instrument sensitivities ≲0.1–0.5 and ≲0.5–3.0 μJy, respectively, with the exact values depending on the nature of primordial dust. However, galaxy populations with higher than typical metallicities, star formation efficiencies, and/or dust-to-metal ratios could relax such sensitivity requirements. In addition, the redshift horizon shows a significant dependence on the nature of primordial dust. We conclude that future FIR campaigns could play a crucial role in exploring the nature of dust and star formation in the early universe.

We assemble an unbiased sample of 29 galaxies with [O ii] λ3727 and/or [O iii] λ5007 detections at z < 0.15 from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Pilot Survey (HPS). The HPS finds galaxies without preselection based on their detected emission lines via integral field spectroscopy. Sixteen of these objects were followed up with the second-generation, low-resolution spectrograph on the upgraded HET. Oxygen abundances were then derived via strong emission lines using a Bayesian approach. We find that most of the galaxies fall along the mass–metallicity relation derived from photometrically selected star-forming galaxies in the Sloan Digital Sky Survey (SDSS). However, two of these galaxies have low metallicity (similar to the very rare green pea galaxies in mass–metallicity space). The star formation rates (SFRs) of this sample fall in an intermediate space between the SDSS star-forming main sequence and the extreme green pea galaxies. We conclude that spectroscopic selection fills a part of the mass–metallicity–SFR phase space that is missed in photometric surveys with preselection like SDSS; i.e., we find galaxies that are actively forming stars but are faint in continuum. We use the results of this pilot investigation to make predictions for the upcoming unbiased, large spectroscopic sample of local line emitters from HETDEX. With the larger HETDEX survey, we will determine if galaxies selected spectroscopically without continuum brightness preselection have metallicities that fall on a continuum that bridges typical star-forming and rarer, more extreme systems like green peas.

Numerous apparent signatures of magnetic reconnection have been reported in the solar photosphere, including inverted-Y shaped jets. The reconnection at these sites is expected to cause localized bidirectional flows and extended shock waves; however, these signatures are rarely observed as extremely high spatial-resolution data are required. Here, we use Hα imaging data sampled by the Swedish Solar Telescope's CRisp Imaging SpectroPolarimeter to investigate whether bidirectional flows can be detected within inverted-Y shaped jets near the solar limb. These jets are apparent in the Hα line wings, while no signature of either jet is observed in the Hα line core, implying reconnection took place below the chromospheric canopy. Asymmetries in the Hα line profiles along the legs of the jets indicate the presence of bidirectional flows, consistent with cartoon models of reconnection in chromospheric anemone jets. These asymmetries are present for over two minutes, longer than the lifetimes of Rapid Blue Excursions, and beyond ±1 Å into the wings of the line indicating that flows within the inverted-Y shaped jets are responsible for the imbalance in the profiles, rather than motions in the foreground. Additionally, surges form following the occurrence of the inverted-Y shaped jets. This surge formation is consistent with models, which suggests such events could be caused by the propagation of shock waves from reconnection sites in the photosphere to the upper atmosphere. Overall, our results provide evidence that magnetic reconnection in the photosphere can cause bidirectional flows within inverted-Y shaped jets and could be the driver of surges.

Supergiant X-ray binaries usually comprise a neutron star accreting from the wind of an OB supergiant companion. They are classified as classical systems and supergiant fast X-ray transients (SFXTs). The different behavior of these subclasses of sources in X-rays, with SFXTs displaying much more pronounced variability, is usually (at least) partly ascribed to different physical properties of the massive star clumpy stellar wind. In the case of SFXTs, a systematic investigation of the effects of clumps on flares/outbursts of these sources has been reported by Bozzo et al. exploiting the capabilities of the instruments on board XMM-Newton to perform a hardness-resolved spectral analysis on timescales as short as a few hundreds of seconds. In this paper, we use six XMM-Newton observations of IGR J18027-2016 to extend the above study to a classical supergiant X-ray binary and compare the findings with those derived in the case of SFXTs. As these observations of IGR J18027-2016 span different orbital phases, we also study its X-ray spectral variability on longer timescales and compare our results with previous publications. Although obtaining measurements of the clump physical properties from X-ray observations of accreting supergiant X-ray binaries has already proven to be challenging, our study shows that similar imprints of clumps are found in the X-ray observations of the SFXTs and at least one classical system, i.e., IGR J18027-2016. This provides interesting perspectives to further extend this study to many XMM-Newton observations already performed in the direction of other classical supergiant X-ray binaries.

Like other young stellar objects (YSOs), FU Ori-type stars have been detected as strong X-ray emitters. However, little is known about how the outbursts of these stars affect their X-ray properties. We assemble available X-ray data from XMM-Newton and Chandra observations of 16 FU Ori stars, including a new XMM-Newton observation of Gaia 17bpi during its optical rise phase. Of these stars, six were detected at least once, while 10 were non-detections, for which we calculate upper limits on intrinsic X-ray luminosity (L_X) as a function of plasma temperature (kT) and column density (N_H). The detected FU Ori stars tend to be more X-ray luminous than is typical for non-outbursting YSOs, based on comparison to a sample of low-mass stars in the Orion Nebula Cluster. FU Ori stars with high L_X have been observed both at the onset of their outbursts and decades later. We use the Kaplan–Meier estimator to investigate whether the higher X-ray luminosities for FU Ori stars are characteristic or a result of selection effects, and we find the difference to be statistically significant (p < 0.01) even when non-detections are taken into account. The additional X-ray luminosity of FU Ori stars relative to non-outbursting YSOs cannot be explained by accretion shocks, given the high observed plasma temperatures. This suggests that, for many FU Ori stars, either (1) the outburst leads to a restructuring of the magnetosphere in a way that enhances X-ray emission, or (2) FU Ori outbursts are more likely to occur among YSOs with the highest quiescent X-ray luminosity.

The hot intracluster plasma in clusters of galaxies is weakly magnetized. Mergers between clusters produce gas compression and motions that can increase the magnetic field strength. In this work, we perform high-resolution nonradiative magnetohydrodynamics simulations of binary galaxy cluster mergers with magnetic fields, to examine the effects of these motions on the magnetic field configuration and strength, as well as the effect of the field on the gas itself. Our simulations sample a parameter space of initial mass ratios and impact parameters. During the first core passage of mergers, the magnetic energy increases via gas compression. After this, shear flows produce temporary, megaparsec-scale, strong-field "filament" structures. Lastly, magnetic fields grow stronger by turbulence. Field amplification is most effective for low-mass ratio mergers, but mergers with a large impact parameter can increase the magnetic energy more via shearing motions. The amplification of the magnetic field is most effective in between the first two core passages of each cluster merger. After the second core passage, the magnetic energy in this region gradually decreases. In general, the transfer of energy from gas motions to the magnetic field is not significant enough to have a substantial effect on gas mixing and the subsequent increase in entropy, which occurs in cluster cores as a result. In the absence of radiative cooling, this results in an overall decrease of the magnetic field strength in cluster cores. In these regions, the final magnetic field is isotropic, while it can be significantly tangential at larger radii.

If the α effect plays a role in the generation of the Sun's magnetic field, the field should show evidence of magnetic helicity of opposite signs at large and small length scales. Measuring this faces two challenges: (i) in weak-field regions, horizontal field measurements are unreliable because of the π ambiguity, and (ii) one needs a truly global approach to computing helicity spectra in the case where one expects a sign reversal across the equator at all wavenumbers. Here we develop such a method using spin-2 spherical harmonics to decompose the linear polarization in terms of the parity-even and parity-odd E and B polarizations, respectively. Using simple one- and two-dimensional models, we show that the product of the spectral decompositions of E and B, taken at spherical harmonic degrees that are shifted by one, can act as a proxy of the global magnetic helicity with a sign that represents that in the northern hemisphere. We then apply this method to the analysis of solar synoptic vector magnetograms, from which we extract a pseudo-polarization corresponding to a "π-ambiguated" magnetic field, i.e., a magnetic field vector that has no arrow. We find a negative sign of the global EB helicity proxy at spherical harmonic degrees of around 6. This could indicate a positive magnetic helicity at large length scales, but the spectrum fails to capture clear evidence of the well-known negative magnetic helicity at smaller scales. This method might also be applicable to stellar and Galactic polarization data.

The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong ${\rm{H}}\alpha$-emitting point source on narrowband ${\rm{H}}\alpha$ images. We present follow-up optical spectroscopy that reveals the presence of a broad ${\rm{H}}\alpha$ component with full width at half maximum of ∼ 290 $\mathrm{km}\,{{\rm{s}}}^{-1}$ in addition to the narrow ${\rm{H}}\alpha$+[N ii] emission features from the host galaxy. Such a broad component is a clear sign of an ejecta–CSM interaction. We also present observations with the XMM-Newton Observatory, the Swift satellite, and the Chandra X-ray Observatory that span 10 days to 15 years after discovery. The detection of strong radio, X-ray, and ${\rm{H}}\alpha$ emission years after explosion allows various constraints to be put on pre-SN mass-loss processes. We present a wind-bubble model in which the CSM is "pre-prepared" by a fast wind interacting with a slow wind. Much of the outer density profile into which the SN explodes corresponds to no steady-state mass-loss process. We estimate that the shell of compressed slow wind material was ejected ∼1400 yr prior to explosion, perhaps during carbon burning, and that the SN shock had swept up about 0.04 ${M}_{\odot }$ of material. The region emitting the ${\rm{H}}\alpha$ has a density of order ${10}^{-20}\,{\rm{g}}\,{\mathrm{cm}}^{-3}$.

We use the gas-grain chemistry code uclchem to explore the impact of cosmic-ray feedback on the chemistry of circumstellar disks. We model the attenuation and energy losses of the cosmic rays as they propagate outward from the star and also consider ionization due to stellar radiation and radionuclides. For accretion rates typical of young stars of ${\dot{M}}_{* }\sim {10}^{-9}\mbox{--}{10}^{-6}$M_⊙ yr⁻¹, we show that cosmic rays accelerated by the stellar accretion shock produce an ionization rate at the disk surface ζ ≳ 10⁻¹⁵ s⁻¹, at least an order of magnitude higher than the ionization rate associated with the Galactic cosmic-ray background. The incident cosmic-ray flux enhances the disk ionization at intermediate to high surface densities (Σ > 10 g cm⁻²), particularly within 10 au of the star. We find that the dominant ions are C⁺, S⁺, and Mg⁺ in the disk surface layers, while the ${{\rm{H}}}_{3}^{+}$ ion dominates at surface densities above 1.0 g cm⁻². We predict the radii and column densities at which the magnetorotational instability (MRI) is active in T Tauri disks and show that ionization by cosmic-ray feedback extends the MRI-active region toward the disk midplane. However, the MRI is only active at the midplane of a minimum-mass solar nebula disk if cosmic rays propagate diffusively (ζ ∝ r⁻¹) away from the star. The relationship between accretion, which accelerates cosmic rays, the dense accretion columns, which attenuate cosmic rays, and the MRI, which facilitates accretion, creates a cosmic-ray feedback loop that mediates accretion and may produce variable luminosity.

Alignment of dust grains in astrophysical environments results in the polarization of starlight as well as the polarization of radiation emitted by dust. We demonstrate the advances in grain alignment theory that allow the use of linear and circular polarization to probe not only the magnetic field, but also dust composition, the dust environment, etc. We revisit the process of grain alignment by Radiative Torques (RATs) and focus on constraining magnetic susceptibility of grains via observations. We discuss the possibility of observational testing of the magnetic properties of grains as the alignment changes from being in respect to the magnetic field to being in respect to the radiation direction. This both opens a possibility of constraining the uncertain parameters of the RATs theory and provides a new way of measuring magnetic fields in the interstellar medium and circumstellar regions. We provide a detailed discussion of the precession induced both by the magnetic field and the anisotropic radiation and revisit a number of key processes related to magnetic response of the grains. We consider various effects that increase the rate of magnetic relaxation both in silicate and carbonaceous grains. In particular, we find a new relaxation process related to the change of the amplitude of internal magnetization within a wobbling triaxial grain and identify a range of grain sizes in which this effect can dominate the internal alignment of angular momentum within grain axes. We show that these relaxation processes significantly change the dynamics of grains in the presence of RATs. We apply our analysis for observed grain alignment in special environments to put constraints on the enhanced magnetic properties of dust grains in the cloud near supernovae, in cometary coma, and protoplanetary disks.

Increasing evidence suggests that He ii proximity profiles in the quasar spectra at z ∼ 3–4 are sensitive probes of quasar ages. But the development of their H i counterparts is difficult to trace and remains poorly constrained. We compare the UV spectra of 15 He ii quasars with their high-resolution optical counterparts and find a significant correlation between the sizes of He ii and H i proximity zones. The luminous quasar HE2347−4342 displays a null proximity zone in both He ii and H i, suggesting that it is extremely young (age < 0.2 Myr). Three other quasars also display small proximity zones for He ii and H i. There is no evidence that a H i ionization zone expands considerably faster than its He ii counterpart. The results suggest that the expansion of quasar ionizing fronts may be noticeably slower than the speed of light, and raise the possibility of distinguishing young and old quasars from the sizes of their H i proximity zones.

In this paper, we investigate the energy partition of two homologous M1.1 circular-ribbon flares (CRFs) in active region (AR) 12434. They were observed by SDO, GOES, and RHESSI on 2015 October 15 and 16, respectively. The peak thermal energy, nonthermal energy of flare-accelerated electrons, total radiative loss of hot plasma, and radiant energies in 1–8 Å and 1–70 Å of the flares are calculated. The two flares have similar energetics. The peak thermal energies are (1.94 ± 0.13) × 10³⁰ erg. The nonthermal energies in flare-accelerated electrons are (3.9 ± 0.7) × 10³⁰ erg. The radiative outputs of the flare loops in 1–70 Å, which are ∼200 times greater than the outputs in 1–8 Å, account for ∼62.5% of the peak thermal energies. The radiative losses of SXR-emitting plasma are one order of magnitude lower than the peak thermal energies. Therefore, the total heating requirements of flare loops including radiative loss are (2.1 ± 0.1) × 10³⁰ erg, which could sufficiently be supplied by nonthermal electrons.

In this work, we investigate the likelihood of association between real-time, neutrino alerts with teraelectronvolt to petaelectronvolt energy from IceCube and optical counterparts in the form of core-collapse supernovae (CC SNe). The optical follow-up of IceCube alerts requires two main instrumental capabilities: (1) deep imaging, since 73% of neutrinos would come from CC SNe at redshifts z > 0.3, and (2) a large field of view (FoV), since typical IceCube muon neutrino pointing accuracy is on the order of ∼1 deg. With Blanco/DECam (gri to 24th magnitude and 2.2 deg diameter FoV), we performed a triggered optical follow-up observation of two IceCube alerts, IC170922A and IC171106A, on six nights during the three weeks following each alert. For the IC170922A (IC171106A) follow-up observations, we expect that 12.1% (9.5%) of coincident CC SNe at z ≲ 0.3 are detectable, and that, on average, 0.23 (0.07) unassociated SNe in the neutrino 90% containment regions also pass our selection criteria. We find two candidate CC SNe that are temporally coincident with the neutrino alerts in the FoV, but none in the 90% containment regions, a result that is statistically consistent with expected rates of background CC SNe for these observations. If CC SNe are the dominant source of teraelectronvolt to petaelectronvolt neutrinos, we would expect an excess of coincident CC SNe to be detectable at the 3σ confidence level using DECam observations similar to those of this work for ∼60 (∼200) neutrino alerts with (without) redshift information for all candidates.

Detecting the cosmological sky-averaged (global) 21 cm signal as a function of observed frequency will provide a powerful tool to study the ionization and thermal history of the intergalactic medium (IGM) in the early universe (∼400 million years after the big bang). The greatest challenge in conventional total-power global 21 cm experiments is the removal of the foreground synchrotron emission (∼10³–10⁴ K) to uncover the weak cosmological signal (tens to hundreds of millikelvin), especially because the intrinsic smoothness of the foreground spectrum is corrupted by instrumental effects. Although the EDGES (Experiment to Detect the Global EoR Signature) team has recently reported an absorption profile at 78 MHz in the sky-averaged spectrum, it is necessary to confirm this detection with an independent approach. The projection effect from observing anisotropic foreground source emission with a wide-view antenna pointing at the North Celestial Pole can induce a net polarization, referred to as the projection-induced polarization effect (PIPE). Due to Earth's rotation, observations centered at the circumpolar region will impose a dynamic sky modulation on the net polarization's waveforms that is unique to the foreground component. In this study, we review the implementation practicality and underlying instrumental effects of this new polarimetry-based technique with detailed numerical simulations and a test-bed instrument, the Cosmic Twilight Polarimeter. In addition, we explore a singular value decomposition–based analysis approach for separating the foreground and instrumental effects from the background global 21 cm signal using the sky-modulated PIPE.

We perform a suite of 3D radiation hydrodynamics simulations of photoevaporation of molecular gas clumps illuminated by external massive stars. We study the fate of solar-mass clumps and derive their lifetimes by varying the gas metallicity over a range of ${10}^{-3}\,{Z}_{\odot }\leqslant Z\leqslant 1{Z}_{\odot }$. Our simulations incorporate radiation transfer of far- and extreme-ultraviolet photons and follow atomic/molecular line cooling and dust–gas collisional cooling. Nonequilibrium chemistry is coupled with the radiative transfer and hydrodynamics in a self-consistent manner. We show that radiation-driven shocks compress gas clumps to have a volume that is set by the pressure equilibrium with the hot ambient gas. Radiative cooling enables metal-rich clumps to condense and have small surface areas where photoevaporative flows are launched. For our fiducial setup with an O-type star at a distance of 0.1 pc, the resulting photoevaporation rate is as small as $\sim {10}^{-5}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ for metal-rich clumps, but it is larger for metal-poor clumps that have larger surface areas. The clumps are continuously accelerated away from the radiation source by the so-called rocket effect and can travel over ∼1 pc within the lifetime. We also study the photoevaporation of clumps in a photodissociation region. Photoelectric heating is inefficient for metal-poor clumps that contain a smaller amount of grains, and thus they survive for over 10⁵ yr. We conclude that the gas metallicity strongly affects the clump lifetime and thus determines the strength of feedback from massive stars in star-forming regions.

We present the first measurements of [Fe/H] and $[\alpha /\mathrm{Fe}]$ abundances, obtained using spectral synthesis modeling, for red giant branch stars in M31's giant stellar stream (GSS). The spectroscopic observations, obtained at a projected distance of 17 kpc from M31's center, yielded 61 stars with [Fe/H] measurements, including 21 stars with $[\alpha /\mathrm{Fe}]$ measurements, from 112 targets identified as M31 stars. The [Fe/H] measurements confirm the expectation from photometric metallicity estimates that stars in this region of M31's halo are relatively metal rich compared to stars in the Milky Way's inner halo: more than half the stars in the field, including those not associated with kinematically identified substructure, have [Fe/H] abundances $\gt -1.0$. The stars in this field are α-enhanced at lower metallicities, while $[\alpha /\mathrm{Fe}]$ decreases with increasing [Fe/H] above metallicities of [Fe/H] ≳ −0.9. Three kinematical components have been previously identified in this field: the GSS, a second kinematically cold feature of unknown origin, and M31's kinematically hot halo. We compare probabilistic [Fe/H] and $[\alpha /\mathrm{Fe}]$ distribution functions for each of the components. The GSS and the second kinematically cold feature have very similar abundance distributions, while the halo component is more metal poor. Although the current sample sizes are small, a comparison of the abundances of stars in the GSS field with abundances of M31 halo and dSph stars from the literature indicate that the progenitor of the stream was likely more massive, and experienced a higher efficiency of star formation, than M31's existing dSphs or the dEs NGC 147 and NGC 185.

The relative column densities of the structural isomers methyl formate, glycolaldehyde, and acetic acid are derived for a dozen positions toward the massive star-forming regions MM1 and MM2 in the NGC 6334I complex, which are separated by ∼4000 au. Relative column densities of these molecules are also gathered from the literature for 13 other star-forming regions. In this combined data set, a clear bimodal distribution is observed in the relative column densities of glycolaldehyde and methyl formate. No such distribution is evident with acetic acid. The two trends are comprised of star-forming regions with a variety of masses, suggesting that there must be some other common parameter that is heavily impacting the formation of glycolaldehyde. This is indicative of some demonstrable differentiation in these cores; studying the abundances of these isomers may provide a clue as to the integral chemical processes ongoing in a variety of protostellar environments.

To reproduce the orbits and masses of the terrestrial planets (analogs) of the solar system, most studies scrutinize simulations for success as a batch. However, there is insufficient discussion in the literature on the likelihood of forming planet analogs simultaneously in the same system (analog system). To address this issue, we performed 540 N-body simulations of protoplanetary disks representative of typical models in the literature. We identified a total of 194 analog systems containing at least three analogs, but only 17 systems simultaneously contained analogs of the four terrestrial planets. From an analysis of our analog systems, we found that, compared to the real planets, truncated disks based on typical outcomes of the Grand Tack model produced analogs of Mercury and Mars that were too dynamically cold and located too close to the Venus and Earth analogs. Additionally, all the Mercury analogs were too massive, while most of the Mars analogs were more massive than Mars. Furthermore, the timing of the Moon-forming impact was too early in these systems, and the amount of additional mass accreted after the event was too great. Therefore, such truncated disks cannot explain the formation of the terrestrial planets. Our results suggest that forming the four terrestrial planets requires disks with the following properties: (1) mass concentrated in narrow core regions between ∼0.7–0.9 au and ∼1.0–1.2 au, (2) an inner region component starting at ∼0.3–0.4 au, (3) a less massive component beginning at ∼1.0–1.2 au, (4) embryos rather than planetesimals carrying most of the disk mass, and (5) Jupiter and Saturn placed on eccentric orbits.

The beamed inverse Compton/cosmic microwave background model has generally been used for the interpretation of X-ray radiation from kiloparsec-scale jets of core-dominated quasars. Recent Fermi-LAT and HST observations have brought this model into question. We examine the assumption that X-rays from the kiloparsec-scale jet of the quasar PKS 1127−145 are produced by inverse Compton scattering of the central source emission. In this context, we show that both similarity and distinction between the observed radio and X-ray spectral indices for some of the jet knots can be explained under a single power-law electron energy distribution. We derive that the viewing angle of the kiloparsec-scale jet is about 35° and the jet has a moderate relativistic speed of ≈0.8c. The predicted gamma-ray flux of the jet is found to be a few orders of magnitude lower than the minimum flux level measured by Fermi-LAT, further supporting our scenario.

The hierarchical galaxy formation model predicts supermassive black hole binaries (SMBHBs) in galactic nuclei. Due to the gas poor environment and the limited spatial resolution in observations they may hide in the center of many a galaxy. However, a close encounter of a star with one of the supermassive black holes (SMBHs) may tidally disrupt it to produce a tidal disruption event (TDE) and temporarily light up the SMBH. In a previous work, we investigated direct N-body simulations with the evolution of TDE rates of SMBHB systems in galaxy mergers of equal mass. In this work we extend the investigation to unequal-mass mergers. Our results show that, when two SMBHs are far away from each other, the TDE rate of each host galaxy is similar as in an isolated galaxy. As the two galaxies and their SMBHs separation shrink, the TDE rate increases gradually until it reaches a maximum shortly after the two SMBHs become bound. In this stage, the averaged TDE rate can be enhanced by several times to an order of magnitude relative to isolated single galaxies. Our simulations show that the dependence of the TDE accretion rate on the mass ratio in this stage can be well fitted by power-law relations for both SMBHs. After the bound SMBHB forms, the TDE rate decreases with its further evolution. We also find that in minor mergers TDEs of the secondary SMBH during and after the bound binary formation are mainly contributed by stars from the other galaxy.

We present limits on the 21 cm power spectrum from the Epoch of Reionization using data from the 64 antenna configuration of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) analyzed through a power spectrum pipeline independent from previous PAPER analyses. Previously reported results from PAPER have been found to contain significant signal loss. Several lossy steps from previous PAPER pipelines have not been included in this analysis, namely delay-based foreground filtering, optimal fringe-rate filtering, and empirical covariance-based estimators. Steps that remain in common with previous analyses include redundant calibration and local sidereal time (LST) binning. The power spectra reported here are effectively the result of applying a linear Fourier transform analysis to the calibrated, LST-binned data. This analysis also uses more data than previous publications, including the complete available redshift range of z ∼ 7.5 to 11. In previous PAPER analyses, many power spectrum measurements were found to be detections of noncosmological power at levels of significance ranging from two to hundreds of times the theoretical noise. Here, excess power is examined using redundancy between baselines and power spectrum jackknives. The upper limits we find on the 21 cm power spectrum from reionization are ${(1500\mathrm{mK})}^{2}$, ${(1900\mathrm{mK})}^{2}$, ${(280\mathrm{mK})}^{2}$, ${(200\mathrm{mK})}^{2}$, ${(380\mathrm{mK})}^{2}$, and ${(300\mathrm{mK})}^{2}$ at redshifts z = 10.87, 9.93, 8.68, 8.37, 8.13, and 7.48, respectively. For reasons described in Cheng et al., these limits supersede all previous PAPER results.

The synchrotron external shock model predicts the evolution of the spectral (β) and temporal (α) indices during the gamma-ray burst (GRB) afterglow for different environmental density profiles, electron spectral indices, electron cooling regimes, and regions of the spectrum. We study the relationship between α and β, the so-called "closure relations" with GRBs detected by Fermi Large Area Telescope (Fermi-LAT) from 2008 August to 2018 August. The spectral and temporal indices for the >100 MeV emission from the Fermi-LAT as determined in the Second Fermi-LAT Gamma-Ray Burst Catalog (2FLGC) are used in this work. We select GRBs whose spectral and temporal indices are well constrained (58 long-duration GRBs and 1 short-duration GRBs) and classify each GRB into the best-matched relation. As a result, we found that a number of GRBs require a very small fraction of the total energy density contained in the magnetic field (_B ≲ 10⁻⁷). The estimated mean and standard deviation of electron spectral index p are 2.40 and 0.44, respectively. The GRBs satisfying a closure relation of the slow cooling tend to have a softer p value compared to those of the fast cooling. Moreover, the Kolmogorov–Smirnov test of the two p distributions from the fast and slow coolings rejects a hypothesis that the two distributions are drawn from the single reference distribution with a significance of 3.2σ. Lastly, the uniform density medium is preferred over the medium that decreases like the inverse of distance squared for long-duration GRBs.

Starburst galaxies and star-forming active galactic nuclei are among the candidate sources thought to contribute appreciably to the extragalactic gamma-ray and neutrino backgrounds. NGC 1068 is the brightest of the star-forming galaxies found to emit gamma-rays from 0.1 to 50 GeV. Precise measurements of the high-energy spectrum are crucial to study the particle accelerators and probe the dominant emission mechanisms. We have carried out 125 hr of observations of NGC 1068 with the MAGIC telescopes in order to search for gamma-ray emission in the very-high-energy band. We did not detect significant gamma-ray emission, and set upper limits at the 95% confidence level to the gamma-ray flux above 200 GeV f < 5.1 × 10⁻¹³ cm⁻² s⁻¹. This limit improves previous constraints by about an order of magnitude and allows us to put tight constraints on the theoretical models for the gamma-ray emission. By combining the MAGIC observations with the Fermi-LAT spectrum we limit the parameter space (spectral slope, maximum energy) of the cosmic ray protons predicted by hadronuclear models for the gamma-ray emission, while we find that a model postulating leptonic emission from a semi-relativistic jet is fully consistent with the limits. We provide predictions for IceCube detection of the neutrino signal foreseen in the hadronic scenario. We predict a maximal IceCube neutrino event rate of 0.07 yr⁻¹.

Supergranules are divergent 30 Mm-sized cellular flows observed everywhere at the solar photosphere. Their place in the hierarchy of convective structures and their origin remain poorly understood. Estimating supergranular depth is of particular interest because this may help point to the underlying physics. However, their subsurface velocity profiles have proven difficult to ascertain. Birch et al. suggested that helioseismic inferences would benefit from an ensemble average over multiple realizations of supergranules due to the reduction in realization noise. Bhattacharya et al. used synthetic forward-modeled seismic wave travel times and demonstrated the potential of helioseismic inversions to recover the flow profile of an average supergranule that is separable in the horizontal and vertical directions, although the premise of this calculation has since been challenged by Ferret. In this work we avoid this assumption and carry out a validation test of helioseismic travel-time inversions starting from plausible synthetic nonseparable profiles of an average supergranule. We compute seismic wave travel times and sensitivity kernels by simulating wave propagation through this background. We find that, while the ability to recover the exact profile degrades based on the number of parameters involved, we are nevertheless able to recover the peak depth of our models in a few iterations where the measurements are presumably above the noise cutoff. This represents an important step toward unraveling the physics behind supergranules, as we start appreciating the parameters that we may reliably infer from a time–distance helioseismic inversion.

PKS 1510-089 is one of the most variable blazars in the third Fermi-LAT source catalog. During 2015, this source has shown four flares identified as flares A, B, C, and D in between three quiescent states: Q1, Q2, and Q3. The multiwavelength data from Fermi-LAT, Swift-XRT/Ultraviolet/Optical Telescope, Owens Valley Radio Observatory, and Sub-millimeter array Observatory are used in our work to model these states. Different flux doubling times have been observed in different energy bands, which indicate that there could be multiple emission zones. The flux doubling time from the gamma-ray and X-ray light curves are found to be 10.6 hr, 2.5 days, and the average flux doubling time in the optical/UV band is 1 day. It is possible that the gamma-ray and optical/UV emission are produced in the same region whereas X-ray emission is coming from a different region along the jet axis. We have also estimated the discrete correlation functions (DCFs) among the light curves of different energy bands to infer about their emission regions. However, our DCF analysis does not show significant correlation in different energy bands though it shows peaks in some cases at small time lags. We perform a two-zone multiwavelength time-dependent modeling with one emission zone located near the outer edge of the broad line region and another further away in the dusty/molecular torus (DT/MT) region to study this high state.

The existence of microgauss magnetic fields in galaxy clusters has been established through observations of synchrotron radiation and Faraday rotation. They are conjectured to be generated via small-scale dynamo by turbulent flow motions in the intracluster medium (ICM). The microgauss magnetic fields of giant radio relics, show structures of synchrotron polarization vectors, organized over scales of megaparsecs, challenging the turbulence origin of cluster magnetic fields. Unlike turbulence in the interstellar medium, turbulence in the ICM is subsonic. And it is driven sporadically in highly stratified backgrounds, when major mergers occur during the hierarchical formation of clusters. To investigate quantitatively the characteristics of a turbulence dynamo in such an ICM environment, we performed a set of turbulence simulations using a high-order-accurate, magnetohydrodynamic (MHD) code. We find that turbulence dynamo could generate the cluster magnetic fields up to the observed level from the primordial seed fields of 10⁻¹⁵ G or so within the age of the universe, if the MHD description of the ICM could be extended down to kiloparsec scales. However, highly organized structures of polarization vectors, such as those observed in the Sausage relic, are difficult to reproduce through the shock compression of turbulence-generated magnetic fields. This implies that the modeling of giant radio relics may require pre-existing magnetic fields organized over megaparsec scales.

We present a numerical framework for the variability of active galactic nuclei (AGNs), which links the variability of AGNs over a broad range of timescales and luminosities to the observed properties of the AGN population as a whole, and particularly the Eddington ratio distribution function. We implemented our framework on GPU architecture, relying on previously published time-series-generating algorithms. After extensive tests that characterize several intrinsic and numerical aspects of the simulations, we describe some applications used for current and future time-domain surveys and for the study of extremely variable sources (e.g., "changing-look" or flaring AGNs). Specifically, we define a simulation setup that reproduces the AGN variability observed in the (intermediate) Palomar Transient Factory survey and use it to forward model longer light curves of the kind that may be observed within the Large Synoptic Survey Telescope (LSST) main survey. Thanks to our efficient implementations, these simulations are able to cover, for example, over 1 Myr with a roughly weekly cadence. We envision that this framework will become highly valuable to prepare for, and best exploit, data from upcoming time-domain surveys,  such as, for example, LSST.

The stellar initial mass function plays a critical role in the history of our universe. We propose a theory that is based solely on local processes, namely the dust opacity limit, the tidal forces, and the properties of the collapsing gas envelope. The idea is that the final mass of the central object is determined by the location of the nearest fragments, which accrete the gas located farther away, preventing it from falling onto the central object. To estimate the relevant statistics in the neighborhood of an accreting protostar, we perform high-resolution numerical simulations. We also use these simulations to further test the idea that fragmentation in the vicinity of an existing protostar is a determinant in setting the peak of the stellar spectrum. We develop an analytical model, which is based on a statistical counting of the turbulent density fluctuations, generated during the collapse, that have a mass at least equal to the mass of the first hydrostatic core, and sufficiently important to supersede tidal and pressure forces to be self-gravitating. The analytical mass function presents a peak located at roughly 10 times the mass of the first hydrostatic core, in good agreement with the numerical simulations. Since the physical processes involved are all local, occurring at scales of a few 100 au or below, and do not depend on the gas distribution at large scale and global properties such as the mean Jeans mass, the mass spectrum is expected to be relatively universal.

We investigate the distribution of companion galaxies around quasars using Hubble Space Telescope (HST) Advanced Camera for Surveys Wide Field Camera (ACS/WFC) archival images. Our master sample contains 532 quasars that have been observed by HST ACS/WFC, spanning a wide range of luminosity (−31 < M_i(z = 2) < −23) and redshift (0.3 < z < 3). We search for companions around the quasars with a projected distance of 10 kpc < d < 100 kpc. Point spread function subtraction is performed to enhance the completeness for close companions. The completeness is estimated to be high (>90%) even for the faintest companions of interest. The number of physical companions is estimated by subtracting a background density from the number density of projected companions. We divide all the companions into three groups (faint, intermediate, and bright) according to their fluxes. A control sample of galaxies is constructed to have a similar redshift distribution and stellar mass range as the quasar sample using the data from HST deep fields. We find that quasars and control sample galaxies have similar numbers of faint and bright companions, while quasars show a 3.7σ deficit of intermediate companions compared to galaxies. The numbers of companions in all three groups do not show strong evolution with redshift, and the number of intermediate companions around quasars decreases with quasar luminosity. Assuming that merger-triggered quasars have entered the final coalescence stage during which individual companions are no longer detectable at large separations, our result is consistent with a picture in which a significant fraction of quasars is triggered by mergers.

We have obtained three-dimensional maps of the universe in ∼200 × 200 × 80 comoving Mpc³ (cMpc³) volumes each at z = 5.7 and 6.6 based on a spectroscopic sample of 179 galaxies that achieves ≳80% completeness down to the Lyα luminosity of $\mathrm{log}({L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\,{{\rm{s}}}^{-1}])=43.0$, based on our Keck and Gemini observations and the literature. The maps reveal filamentary large-scale structures and two remarkable overdensities made out of at least 44 and 12 galaxies at z = 5.692 (z57OD) and z = 6.585 (z66OD), respectively, making z66OD the most distant overdensity spectroscopically confirmed to date, with >10 spectroscopically confirmed galaxies. We compare spatial distributions of submillimeter galaxies at z ≃ 4–6 with our z = 5.7 galaxies forming the large-scale structures, and detect a 99.97% signal of cross-correlation, indicative of a clear coincidence of dusty star-forming galaxy and dust-unobscured galaxy formation at this early epoch. The galaxies in z57OD and z66OD are actively forming stars with star-formation rates (SFRs) ≳5 times higher than the main sequence, and particularly the SFR density in z57OD is 10 times higher than the cosmic average at the redshift (a.k.a. the Madau-Lilly plot). Comparisons with numerical simulations suggest that z57OD and z66OD are protoclusters that are progenitors of the present-day clusters with halo masses of ∼10¹⁴M_⊙.

We show that the total habitable volume in the atmospheres of cool brown dwarfs with effective temperatures of ∼250–350 K is possibly larger by 2 orders of magnitude than that of Earth-like planets. We also study the role of aerosols, nutrients, and photosynthesis in facilitating life in brown dwarf atmospheres. Our predictions might be testable through searches for spectral edges in the near-infrared and chemical disequilibrium in the atmospheres of nearby brown dwarfs that are either free-floating or within several au of stars. For the latter category, we find that the James Webb Space Telescope may be able to achieve a signal-to-noise ratio of ∼5 after a few hours of integration time per source for the detection of biogenic spectral features in ∼10³ cool brown dwarfs.

Clouds are ubiquitous in extrasolar planet atmospheres and are critical to our understanding of planetary climate and chemistry. They also represent one of the greater challenges to overcome when trying to interpret transit transmission spectra of exoplanet atmospheres as their presence can inhibit precise constraints on atmospheric composition and thermal properties. In this work, we take a phenomenological approach toward understanding (1) our ability to constrain bulk cloud properties and (2) the impact of clouds on constraining various atmospheric properties as obtained through transmission spectroscopy with the James Webb Space Telescope (JWST). We do this by exploring retrievals of atmospheric and cloud properties for a generic "hot Jupiter" as a function of signal-to-noise ratio (S/N), JWST observing modes, and four different cloud parameterizations. We find that most key atmospheric and cloud inferences can be well constrained in the wavelength range (λ = 0.6–11 μm), with NIRCam (λ = 2.5–5 μm) being critical in inferring atmospheric properties and NIRISS + MIRI (λ = 0.6–2.5, 5–11 μm) being necessary for good constraints on cloud parameters. However, constraining the cloud abundance and therefore the total cloud mass requires an observable cloud base in the transit geometry. While higher S/N observations can place tighter constraints on major parameters such as temperature, metallicity, and cloud sedimentation, they are unable to eliminate strong degeneracies among cloud parameters. Our investigation of a generic "warm Neptune" with photochemical haze parameterization also shows promising results in constraining atmospheric and haze properties in the cooler temperature regime.

We present the first high-resolution map of the cold molecular gas distribution as traced by CO(2−1) emission with ALMA in a long ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is undergoing a strong interaction with the surrounding intracluster medium and is one of the nearest jellyfish galaxies with a long multiphase and multicomponent tail. We have mapped the full extent of the tail at 1'' (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total, about 10⁹M_⊙ of molecular gas was detected with ALMA. From comparison with previous APEX observations, we also infer the presence of a substantial extended molecular component in the tail. The ALMA CO features are found predominantly at the heads of numerous small-scale (∼1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also large-scale (∼8 kpc) superfireballs and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite the stellar tails. The new data help to shed light on the origin of the molecular tail; CO filaments oriented in the direction of the tail are likely young molecular features formed in situ, whereas large CO features tilted with respect to the tail may have originated from dense gas complexes that were gradually pushed away from the disk.

A double adiabatically expanding solar wind would quickly develop large parallel to perpendicular temperature anisotropies in electrons and ions that are not observed. One reason is that firehose instabilities would be triggered, leading to an ongoing driving/saturation evolution mechanism. We verify this assumption here for the first time for the electron distribution function and the electron firehose instability (EFI), using fully kinetic simulations with the Expanding Box Model. This allows the self-consistent study of onset and evolution of the oblique, resonant EFI in an expanding solar wind. We characterize how the competition between EFI and adiabatic expansion plays out in high- and low-beta cases, in high- and low-speed solar wind streams. We observe that, even when competing against expansion, the EFI results in perpendicular heating and parallel cooling. These two concurrent processes effectively limit the expansion-induced increase in temperature anisotropy and parallel electron beta. We show that the EFI goes through cycles of stabilization and destabilization: when higher wave number EFI modes saturate, lower wave number modes are destabilized by the effects of the expansion. We show how resonant wave/ particle interaction modifies the electron velocity distribution function after the onset of the EFI. The simulations are performed with the fully kinetic, semi-implicit expanding box code EB-iPic3D.

We present comprehensive observations and analysis of the energetic H-stripped SN 2016coi (a.k.a. ASASSN-16fp), spanning the γ-ray through optical and radio wavelengths, acquired within the first hours to ∼420 days post explosion. Our observational campaign confirms the identification of He in the supernova (SN) ejecta, which we interpret to be caused by a larger mixing of Ni into the outer ejecta layers. By modeling the broad bolometric light curve, we derive a large ejecta-mass-to-kinetic-energy ratio (M_ej ∼ 4–7 M_⊙, E_k ∼ (7–8) × 10⁵¹ erg). The small [Ca ii] λλ7291,7324 to [O i] λλ6300,6364 ratio (∼0.2) observed in our late-time optical spectra is suggestive of a large progenitor core mass at the time of collapse. We find that SN 2016coi is a luminous source of X-rays (L_X > 10³⁹ erg s⁻¹ in the first ∼100 days post explosion) and radio emission (L_{8.5 GHz} ∼ 7 × 10²⁷ erg s⁻¹ Hz⁻¹ at peak). These values are in line with those of relativistic SNe (2009bb, 2012ap). However, for SN 2016coi, we infer substantial pre-explosion progenitor mass loss with a rate $\dot{M}$ ∼ (1–2) × ${10}^{-4}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ and a sub-relativistic shock velocity v_sh ∼ 0.15c, which is in stark contrast with relativistic SNe and similar to normal SNe. Finally, we find no evidence for a SN-associated shock breakout γ-ray pulse with energy E_γ > 2 × 10⁴⁶ erg. While we cannot exclude the presence of a companion in a binary system, taken together, our findings are consistent with a massive single-star progenitor that experienced large mass loss in the years leading up to core collapse, but was unable to achieve complete stripping of its outer layers before explosion.

We investigate the dynamics of a closed-corona Cartesian reduced magnetohydrodynamic model where photospheric vortices twist the coronal magnetic field lines. We consider two corotating or counterrotating vortices localized at the center of the photospheric plate and, additionally, more corotating vortices that fill the plate entirely. Our investigation is specifically devoted to studying the fully nonlinear stage, after the linear stage during which the vortices create laminar and smoothly twisting flux tubes. Our main goal is to understand the dynamics of the photospheric vortices twisting the field lines of a coronal magnetic configuration permeated by finite-amplitude broadband fluctuations. We find that, depending on the system parameters and the arrangement and handedness of the photospheric vortices, an inverse cascade storing a significant amount of magnetic energy may or may not occur. In the first case, a reservoir of magnetic energy available to large events, such as destabilization of a pre–coronal mass ejection (CME) configuration, develops, while in the second case, the outcome is a turbulent heated corona. Although our geometry is simplified, our simulations are shown to have relevant implications for coronal dynamics and CME initiation.

When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ≳100 Gpc⁻³ yr⁻¹ for e > 0.1, assuming a black hole mass spectrum with a power-law index ≲2.

Solar flares originate from magnetically active regions (ARs) but not all solar ARs give rise to a flare. Therefore, the challenge of solar flare prediction benefits from an intelligent computational analysis of physics-based properties extracted from AR observables, most commonly line-of-sight or vector magnetograms of the active region photosphere. For the purpose of flare forecasting, this study utilizes an unprecedented 171 flare-predictive AR properties, mainly inferred by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO/HMI) in the course of the European Union Horizon 2020 FLARECAST project. Using two different supervised machine-learning methods that allow feature ranking as a function of predictive capability, we show that (i) an objective training and testing process is paramount for the performance of every supervised machine-learning method; (ii) most properties include overlapping information and are therefore highly redundant for flare prediction; (iii) solar flare prediction is still—and will likely remain—a predominantly probabilistic challenge.

It has been suggested that the isotropic electron halo observed in the solar wind electron velocity distribution function may originate from nanoflare-accelerated electron beams below 1.1 R_⊙ from the solar surface through the nonlinear electron two-stream instability (ETSI). This model unifies the origins of kinetic waves, the electron halo, and the coronal weak Type III bursts, and establishes a link between the solar wind observables and the electron dynamics in nanoflares. One of the important predictions of this model is that the halo-core temperature ratio is anticorrelated with the density ratio, and the minimum ratio is ∼4, a relic of the ETSI heating and has been found to be consistent with solar wind observations. However, how the density and relative drift of the electron beams determine the thermal properties of solar wind electrons is unclear. In this paper, using a set of particle-in-cell simulations and kinetic theory, we show that a necessary condition for an isotropic halo to develop is that the ratio of beam density n_b and the background n₀ be lower than a critical value N_c ∼ 0.3. Heating of the core electrons becomes weaker with decreasing beam density, while the heating of halo electrons becomes stronger. As a result, the temperature ratio of the halo and core electrons increases with the decrease of the beam density, explaining the physical meaning of the predicted anticorrelated relation. We apply these results to the current observations and discuss the possible electron beam density produced in the nanoflares.

Helmet streamers are a prominent manifestation of magnetic structures with current sheets in the solar corona. These large-scale structures are regions with high plasma density, overlying active regions and filament channels. We investigate the three-dimensional (3D) structure of a coronal streamer, observed simultaneously by white-light coronagraphs from two vantage points near quadrature (the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph Experiment (LASCO) and the Solar Terrestrial Relations Observatory (STEREO)/Coronagraph 2 (COR2)). We design a forward model based on plausible assumptions about the 3D streamer structure taken from physical models (a plasma slab centered around a current sheet). The streamer stalk is approximated by a plasma slab, with an electron density that is characterized by three separate functions describing the radial, transverse, and face-on profiles, respectively. For the first time, we simultaneously fit the observational data from SOHO and STEREO using a multivariate minimization algorithm. The streamer plasma sheet contains a number of brighter and darker ray-like structures with the density contrast up to about a factor of 3 between them. The densities derived using polarized and unpolarized data are similar. We demonstrate that our model corresponds well to the observations.

The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck I: one at z = 2.095 in COSMOS and another at z = 1.62 in UKIRT Infrared Deep Sky Survey (UDS). Here, we use an updated ZFIRE data set to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines Hβ 4861 Å, [O iii] 5007 Å, Hα 6563 Å, [N ii] 6585 Å, and [S ii] 6716,6731 Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of the ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass–Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which report no significant gas-phase metallicity offset between proto-cluster and field galaxies until z = 1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that indicate UDS high-mass proto-cluster and field galaxies have differing [O iii]/Hβ ratios; however, these results are dependent on the sample size of the high-mass stacks.

We report the discovery of a mid-infrared variable AGN that is hosted by an ultraluminous infrared galaxy (ULIRG) in the Sloan Stripe 82 field. WISE J030654.88+010833.6 is a red, extended galaxy, which we estimate to be at a photometric redshift of 0.28 ≤ z ≤ 0.31, based on its optical and near-infrared spectral energy distribution (SED). The factor of two variability over 8 yr seen in the Wide-field Infrared Survey Explorer (WISE) 3.4 and 4.6 μm wavelength channels is not clearly correlated with optical variability in archival data. Based on our estimation of the physical parameters of the host galaxy, J030654.88+010833.6 is possibly a composite AGN/starburst ULIRG in a phase where high star formation ∼70 M_⊙ yr⁻¹ is occurring. Our estimate of the black hole mass to stellar mass ratio also appears to be consistent with that of broad line AGN in the local universe. The long-term variability of J030654.88+010833.6 as seen in the WISE W1 and W2 light curves is likely due to variations in the accretion rate, with the energy being reprocessed by dust in the vicinity of the AGN.

In the CDM paradigm, the halo mass function is a sensitive probe of the cosmic structure. In observations, halo mass is typically estimated from its relation with other observables. The resulting halo mass function is subject to systematic bias, such as the Eddington bias, due to the scatter or uncertainty in the observable–mass relation. Exact correction for the bias is not easy, as predictions for the observables are typically model-dependent in simulations. In this paper, we point out an interesting feature in the halo mass function of the concordance ΛCDM model: the total halo mass within each evenly spaced logarithmic mass bin is approximately the same over a large mass range. We show that this property allows us to construct an almost bias-free halo mass function using only an observable (as a halo mass estimator) and stacked weak lensing measurements as long as the scatter between the true halo mass and the observable-inferred mass has a stable form in logarithmic units. The method is not sensitive to the form of the mass–observable relation. We test the idea using cosmological simulations, and show that the method performs very well for realistic observables.

We report the statistical physical properties of the C¹⁸O(J = 1–0) clumps present in a prominent cluster-forming region, Cygnus X, using the data set obtained by the Nobeyama 45 m radio telescope. This survey covers 9 deg² of the northern and southern regions of Cygnus X, and, in total, 174 C¹⁸O clumps are identified using the dendrogram method. Assuming a distance of 1.4 kpc, these clumps have radii of 0.2–1 pc, velocity dispersions of <2.2 km s⁻¹, gas masses of 30–3000 M_⊙, and H₂ densities of (0.2–5.5) × 10⁴ cm⁻³. We confirm that the C¹⁸O clumps in the northern region have a higher H₂ density than those in the southern region, supporting the existence of a difference in the evolutionary stages, consistent with the star-formation activity of these regions. The difference in the clump properties of the star-forming and starless clumps is also confirmed by the radius, velocity dispersion, gas mass, and H₂ density. The average virial ratio of 0.3 supports that these clumps are gravitationally bound. The C¹⁸O clump mass function shows two spectral index components, α = −1.4 in 55–140 M_⊙ and α = −2.1 in >140 M_⊙, which are consistent with the low- and intermediate-mass parts of the Kroupa's initial mass function. The spectral index of the star-forming clumps >140 M_⊙ is consistent with that of the starless clumps ranging from 55–140 M_⊙, suggesting that the latter will evolve into star-forming clumps while retaining the gas accretion. Assuming a typical star-formation efficiency of molecular clumps (10%), about 10 C¹⁸O clumps having a gas mass of >10³M_⊙ will evolve into open clusters containing one or more OB stars.

We investigate the accuracy of 4000 Å/Balmer-break based redshifts by combining Hubble Space Telescope (HST) grism data with photometry. The grism spectra are from the Probing Evolution And Reionization Spectroscopically survey with HST using the G800L grism on the Advanced Camera for Surveys. The photometric data come from a compilation by the 3D-HST collaboration of imaging from multiple surveys (notably, the Cosmic Assembly Near-infrared Deep Extragalactic Survey (CANDELS) and 3D-HST). We show evidence that spectrophotometric redshifts (SPZs) typically improve the accuracy of photometric redshifts by ∼17%–60%. Our SPZ method is a template-fitting-based routine that accounts for correlated data between neighboring points within grism spectra via the covariance matrix formalism and also accounts for galaxy morphology along the dispersion direction. We show that the robustness of the SPZ is directly related to the fidelity of the D4000 measurement. We also estimate the accuracy of continuum-based redshifts, i.e., for galaxies that do not contain strong emission lines, based on the grism data alone (${\sigma }_{{\rm{\Delta }}z/(1+z)}^{\mathrm{NMAD}}\lesssim 0.06$). Given that future space-based observatories like Wide Field InfraRed Survey Telescope and Euclid will spend a significant fraction of time on slitless spectroscopic observations, we estimate number densities for objects with $\left|{\rm{\Delta }}z/(1+{z}_{s})\right|\leqslant 0.02$. We predict ∼700–4400 galaxies degree⁻² for galaxies with D4000 > 1.1 and $\left|{\rm{\Delta }}z/(1+{z}_{{\rm{s}}})\right|\leqslant 0.02$ to a limiting depth of i_AB = 24 mag. This is especially important in the absence of an accompanying rich photometric data set like the existing one for the CANDELS fields, where redshift accuracy from future surveys will rely only on the presence of a feature like the 4000 Å/Balmer breaks or the presence of emission lines within the grism spectra.

We report the results from a new, highly sensitive (ΔT_mb ∼ 3 mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 × 9 pixel grid covering a 1° × 1° patch of sky in the direction of l = 10500, b = +250 toward the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope 1667 MHz OH results with archival ¹²CO(1–0) observations from the Five College Radio Astronomy Observatory Outer Galaxy Survey within the velocity range of the Perseus Arm at these galactic coordinates. Out of the 81 statistically independent pointings in our survey area, 86% show detectable OH emission at 1667 MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits below an A_v of 0.2, but the CO emission does not appear until the volume density exceeds 100–200 ${\mathrm{cm}}^{-3}$. These results demonstrate that a combination of low column density A_v and low volume density n_H can explain the lack of CO emission along sight lines exhibiting OH emission. The 18 cm OH main lines, with their low critical density of n* ∼ 1 ${\mathrm{cm}}^{-3}$, are collisionally excited over a large fraction of the quiescent galactic environment and, for observations of sufficient sensitivity, provide an optically thin radio tracer for diffuse H₂.

The "Breakthrough Starshot" program is planning to send transrelativistic probes to travel to nearby stellar systems within decades. Because the probe velocity is designed to be a good fraction of the light speed, Zhang & Li recently proposed that these transrelativistic probes can be used to study astronomical objects and to test special relativity. In this work, we propose some methods to test special relativity and constrain photon mass using the Doppler effect with the images and spectral features of astronomical objects as observed in the transrelativistic probes. We introduce more general theories to set up the framework of testing special relativity, including the parametric general Doppler effect and the Doppler effect with massive photons. We find that by comparing the spectra of a certain astronomical object, one can test Lorentz invariance and constrain photon mass. Additionally, using the imaging and spectrograph capabilities of transrelativistic probes, one can test time dilation and constrain photon mass. For a transrelativistic probe with velocity v ∼ 0.2c, aperture D ∼ 3.5 cm, and spectral resolution R ∼ 100 (or 1000), we find that the probe velocity uncertainty can be constrained to σ_v ∼ 0.01c (or 0.001c), and the time dilation factor uncertainty can be constrained to ${\rm{\Delta }}\gamma =| \hat{\gamma }-\gamma | \lesssim 0.01$ (or 0.001), where $\hat{\gamma }$ is the time dilation factor and γ is the Lorentz factor. Meanwhile, the photon mass limit is set to m_γ ≲ 10⁻³³ g, which is slightly lower than the energy of the optical photon.

We investigate the feedback of the stellar jets on the surrounding interstellar gas based on 2D and 3D simulations applying HD and MHD modules of the PLUTO 4.2 code. The main question we address is whether the stellar jet can be considered as a turbulence driver into the interstellar gas. In addition, we investigate the most effective circumstances in which the driven turbulence is larger and can survive for a longer timescale in the ambient gas. We present a case study of different parameter runs including the jet Mach number, the initial jet velocity field, the background magnetic field geometries and the interacting jets. We also study the environmental effects on the jet-gas interaction by considering the non-homogeneous surrounding gas containing the clumps in the model setup. Among different setups, we find (1) a higher jet Mach number, (2) a rotating jet, (3) a jet propagating in a magnetized environment, (4) a jet propagating in a non-homogeneous environment, and (5) the interacting jets produce more fluctuations and random motions in the entrained gas, which can survive for a longer timescale. In addition, we perform the 3D simulations of jet-ambient gas interaction and we find that the amount of (subsonic–supersonic) fluctuation increases compared to the axisymmetric run, and the entrained gas gains higher velocities in a 3D run. In total, we confirm the previous finding that the stellar jets can transfer the turbulence on neighboring regions and are not sufficient drivers of the large-scale supersonic turbulence in molecular clouds.

In the vicinity of a massive black hole, stars move on precessing Keplerian orbits. The mutual stochastic gravitational torques between the stellar orbits drive a rapid reorientation of their orbital planes, through a process called vector resonant relaxation. We derive, from first principles, the correlation of the potential fluctuations in such a system, and the statistical properties of random walks undergone by the stellar orbital orientations. We compare this new analytical approach with numerical simulations. We also provide a simple scheme to generate the random walk of a test star's orbital orientation using a stochastic equation of motion. We finally present quantitative estimations of this process for a nuclear stellar cluster such as that of the Milky Way.

GRB 190114C, a long and luminous burst, was detected by several satellites and ground-based telescopes from radio wavelengths to GeV gamma-rays. In the GeV gamma-rays, the Fermi Large Area Telescope detected 48 photons above 1 GeV during the first 100 s after the trigger time, and the MAGIC telescopes observed for more than 1000 s very high-energy (VHE) emission above 300 GeV. Previous analysis of the multi-wavelength observations showed that, although these are consistent with the synchrotron forward-shock model that evolves from a stratified stellar-wind to a homogeneous ISM-like medium, photons above a few GeV can hardly be interpreted in the synchrotron framework. In the context of the synchrotron forward-shock model, we derive the light curves and spectra of the synchrotron self-Compton (SSC) model in a stratified and homogeneous medium. In particular, we study the evolution of these light curves during the stratified-to-homogeneous afterglow transition. Using the best-fit parameters reported for GRB 190114C we interpret the photons beyond the synchrotron limit in the SSC framework and model its spectral energy distribution. We conclude that low-redshift gamma-ray bursts described under a favorable set of parameters as found in the early afterglow of GRB 190114C could be detected at hundreds of GeV, and also afterglow transitions would allow that VHE emission could be observed for longer periods.

We present a survey for metal absorption systems traced by neutral oxygen over 3.2 < z < 6.5. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total, we detect 74 O i absorbers, of which 57 are separated from the background QSO by more than 5000 km s⁻¹. We use a maximum likelihood approach to fit the distribution of O i λ1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with W₁₃₀₂ > 0.05 Å, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 < z < 5.7 is a factor of 1.7–4.1 lower (68% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z ∼ 6 than at lower redshifts. Absorption from highly ionized metals traced by C iv is also weaker in higher-redshift O i systems, supporting this picture. The evolution of O i absorbers implies that metal-enriched circumgalactic gas at z ∼ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.

Chondrules are silicate spheroids found in meteorites, and they serve as important fossil records of the early solar system. In order to form chondrules, chondrule precursors must be heated to temperatures much higher than the typical conditions in the current asteroid belt. One proposed mechanism for chondrule heating is the passage through bow shocks of highly eccentric planetesimals in the protoplanetary disk in the early solar system. However, it is difficult for planetesimals to gain and maintain such high eccentricities. In this paper, we present a new scenario in which planetesimals in the asteroid belt region are excited to high eccentricities by the Jovian sweeping secular resonance in a depleting disk, leading to efficient formation of chondrules. We study the orbital evolution of planetesimals in the disk using semi-analytic models and numerical simulations. We investigate the dependence of eccentricity excitation on the planetesimal's size, as well as the physical environment and the probability for chondrule formation. We find that 50–2000 km planetesimals can obtain eccentricities larger than 0.6 and cause effective chondrule heating. Most chondrules form in high-velocity shocks, in low-density gas, and in the inner disk. The fraction of chondrule precursors that become chondrules is about 4%–9% between 1.5 and 3 au. Our model implies that the disk depletion timescale is τ_dep ≈ 1 Myr, comparable to the age spread of chondrules, and that Jupiter formed before chondrules, no more than 0.7 Myr after the formation of calcium aluminum inclusions.

Temporal variation of millimeter lines is a new direction of research for evolved stars. It has the potential to probe the dynamical wind-launching processes from a time dimension. We report here the first Atacama Large Millimeter Array (ALMA) results that cover 817 days of ongoing monitoring of 1.1 mm lines in the archetypal carbon star IRC +10216. The monitoring is done with the compact 7 m array and in infrared with a 1.25 m telescope in Crimea. High sensitivity of the cumulative spectra covering a total of ∼7.2 GHz between 250 and 270 GHz has allowed us to detect about 148 known transitions of 20 molecules, together with more of their isotopologues, and 81 unidentified lines. An overview of the variabilities of all detected line features is presented in spectral plots. Although a handful of lines are found to be very possibly stable in time, most other lines are varying either roughly in phase or in anticorrelation with the near-infrared light. Several lines have their variations in the ALMA data coincident with existing single-dish monitoring results, while several others do not, which requires a yet-unknown mechanism in the circumstellar envelope to explain.

We introduce new color indices ${{cn}}_{\mathrm{JWL}}^{{\prime} }$ (=Ca_CTIO − Ca_JWL) and ch_JWL [=(JWL43 − b) − (b − y)], accurate photometric measures of the CN band at λ3883 and the CH G band, respectively, in the study of the multiple populations (MPs) in globular clusters (GCs). Our photometric CN–CH relation for a large number of red-giant branch (RGB) in M5 shows that the evolutions of the CN and CH between the CN-w and CN-s populations are not continuous. Armed with our new color indices, we investigate the MPs of NGC 6723, finding the RGB populational number ratio of n(CN-w):n(CN-s) ≈ 35.5:64.5 (±2.8) with no radial gradient. Similar to other normal GCs with MPs, the helium abundance of the CN-s population inferred from the RGB bump magnitude is slightly enhanced by ΔY = 0.012 ± 0.012. Our cn_JWL and ${{cn}}_{\mathrm{JWL}}^{{\prime} }$ color–magnitude diagrams clearly show the discrete double asymptotic giant branch (AGB) populations in NGC 6723, whose bright AGB populational number ratio is in marginal agreement with that of the RGB stars within the statistical errors. Finally, our synthetic cn_JWL index is in good agreement with observations, except for the CN-w AGB. Mitigation of the discrepancy in the CN-w AGB may require a mild nitrogen enhancement and/or a large decrement in the ¹²C/¹³C ratio with respect to the bright RGB.

The coevolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of ΛCDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with mutual separations <10 kpc in the advanced merger SDSS J084905.51+111447.2 at z = 0.077. The system exhibits three nuclear X-ray sources, optical spectroscopic line ratios consistent with AGN in each nucleus, a high excitation near-IR coronal line in one nucleus, and broad Paα detections in two nuclei. Hard X-ray spectral fitting reveals a high column density along the line of sight, consistent with the picture of late-stage mergers hosting heavily absorbed AGNs. Our multiwavelength diagnostics support a triple AGN scenario, and we rule out alternative explanations such as star formation activity, shock-driven emission, and emission from fewer than three AGN. The dynamics of gravitationally bound triple SMBH systems can dramatically reduce binary SMBH inspiral timescales, providing a possible means to surmount the "Final Parsec Problem." AGN triplets in advanced mergers are the only observational forerunner to bound triple SMBH systems and thus offer a glimpse of the accretion activity and environments of the AGNs prior to the gravitationally bound triple phase.

We analyze the effects of including Δ(1232) isobars in an equation of state (EoS) for cold, β-stable neutron star (NS) matter, employing relativistic nuclear mean field theory. The selected EoS reproduces the properties of nuclear matter and finite nuclei and, in the astrophysical context, allows for the presence of hyperons in NSs having masses larger than 2 M_⊙. We find that the composition and structure of NSs is critically influenced by the addition of the Δ isobars, which allows us to constrain their interaction with the meson fields, taking into account astrophysical information. Imposing that the EoS is stable and ensures the existence of 2 M_⊙ NSs, as well as requiring agreement with data of Δ excitation in nuclei, we find that, in the absence of other mechanisms stiffening the EoS at high densities, the interaction of the Δ isobars with the sigma and omega meson fields must be at least 10% stronger than those of the nucleons. Moreover, the NS moment of inertia turns out to be sensitive to the presence of Δ isobars, whereas the inclusion of Δ isobars in the EoS allows for smaller stellar radii and for a lower value of the tidal deformability, consistent with the analysis of the GW170817 merger event.

We discuss prospects of identifying and characterizing black hole (BH) companions to normal stars on tight but detached orbits, using photometric data from the Transiting Exoplanet Survey Satellite (TESS). We focus on the following two periodic signals from the visible stellar component: (i) in-eclipse brightening of the star due to gravitational microlensing by the BH (self-lensing), and (ii) a combination of ellipsoidal variations due to tidal distortion of the star and relativistic beaming due to its orbital motion (phase-curve variation). We evaluate the detectability of each signal in the light curves of stars in the TESS input catalog, based on a pre-launch noise model of TESS photometry as well as the actual light curves of spotted stars from the prime Kepler mission to gauge the potential impact of stellar activity arising from the tidally spun-up stellar components. We estimate that the self-lensing and phase-curve signals from BH companions, if they exist, will be detectable in the light curves of effectively ${ \mathcal O }({10}^{5})$ and ${ \mathcal O }({10}^{6})$ low-mass stars, respectively, taking into account orbital inclination dependence of the signals. These numbers could be large enough to actually detect signals from BHs: simple population models predict some 10 and 100 detectable BHs among these "searchable" stars; although, the latter may be associated with a comparable number of false positives due to stellar variabilities, and additional vetting with radial velocity measurements would be essential. Thus, the TESS data could serve as a resource to study nearby BHs with stellar companions on shorter-period orbits than will potentially be probed with Gaia.

Quasars have been proposed as a new class of standard candles analogous to supernovae, since their large redshift range and high luminosities make them excellent candidates. The reverberation mapping (RM) method enables one to estimate the distance to the source from the time delay measurement of the emission lines with respect to the continuum, since the time delay depends on the absolute luminosity of the source. The radius–luminosity relation exhibits a low scatter and offers a potential use in cosmology. However, in recent years, the inclusion of new sources, particularly the super-Eddington accreting QSO, has increased the dispersion in the radius–luminosity relation, with many objects showing time delays shorter than the expected. Using 117 Hβ reverberation-mapped active galactic nuclei with 0.002 < z < 0.9 and 41.5 < log L₅₁₀₀ < 45.9, we find a correction for the time delay based on the dimensionless accretion rate ($\dot{{\mathscr{M}}}$) considering a virial factor anticorrelated with the FWHM of Hβ. This correction decreases the scattering of the accretion parameters compared with the typical values used, which is directly reflected by suppressing the radius–luminosity relation dispersion. We also confirm the anticorrelation between the excess of variability and the accretion parameters. With this correction, we are able to build the Hubble diagram and estimate the cosmological constants Ω_m and Ω_Λ, which are consistent with the Λ Cold Dark Matter model at 2σ confidence level. Therefore, reverberation mapping results can be used to constrain cosmological models in the future.

This paper presents an alternative scenario to explain the observed properties of the Milky Way dwarf Spheroidals (MW dSphs). We show that instead of resulting from large amounts of dark matter (DM), the large velocity dispersions observed along their lines of sight (σ_los) can be entirely accounted for by dynamical heating of DM-free systems resulting from MW tidal shocks. Such a regime is expected if the progenitors of the MW dwarfs are infalling gas-dominated galaxies. In this case, gas lost through ram-pressure leads to a strong decrease of self-gravity, a phase during which stars can radially expand, while leaving a gas-free dSph in which tidal shocks can easily develop. The DM content of dSphs is widely derived from the measurement of the dSphs self-gravity acceleration projected along the line of sight. We show that the latter strongly anti-correlates with the dSph distance from the MW, and that it is matched in amplitude by the acceleration caused by MW tidal shocks on DM-free dSphs. If correct, this implies that the MW dSphs would have negligible DM content, putting in question, e.g., their use as targets for DM direct searches, or our understanding of the Local Group mass assembly history. Most of the progenitors of the MW dSphs are likely extremely tiny dIrrs, and deeper observations and more accurate modeling are necessary to infer their properties as well as to derive star formation histories of the faintest dSphs.

Magnetohydrodynamic (MHD) theory and simulations have shown that reconnection is triggered via a fast "ideal" tearing instability in current sheets whose inverse aspect ratio decreases to $a/L\sim {S}^{-1/3}$, with S as the Lundquist number defined by the half-length L of the current sheet (of a thickness of 2a). Ideal tearing, in 2D sheets, triggers a hierarchical collapse via stretching of X-points and recursive instability. At each step, the local Lundquist number decreases, until the subsequent sheet thickness either approaches kinetic scales or the Lundquist number becomes sufficiently small. Here we carry out a series of Hall-MHD simulations to show how the Hall effect modifies recursive reconnection once the ion inertial scale is approached. We show that as the ion inertial length becomes of the order of the inner, singular layer thickness at some step of the recursive collapse, reconnection transits from the plasmoid-dominant regime to an intermediate plasmoid+Hall regime and then to the Hall-dominant regime. The structure around the X-point, the reconnection rate, the dissipation property, and the power spectra are also modified significantly by the Hall effect.

IRAS F11119+3257 is a quasar-dominated ultraluminous infrared galaxy, with a partially obscured narrow-line Seyfert 1 nucleus. In this paper, we present the near-IR (NIR) spectroscopy of F11119+3257, in which we find unusual Paschen emission lines and metastable He i* λ10830 absorption associated with the previously reported atomic sodium and molecular OH mini-BAL (broad absorption line) outflow. Photoionization diagnosis confirms previous findings that the outflows are at kiloparsec scales. Such large-scale outflows should produce emission lines. We indeed find that high-ionization emission lines ([O III], [Ne III], and [Ne V]) are dominated by blueshifted components at similar speeds to the mini-BALs. The blueshifted components are also detected in some low-ionization emission lines, such as [O II] λ3727 and some Balmer lines (Hα, Hβ, and Hγ), even though their cores are dominated by narrow (FWHM_NEL = 570 ± 40  km s⁻¹) or broad components at the systemic redshift of z = 0.18966 ± 0.00006. The mass flow rate (230–730 M_⊙ yr⁻¹) and the kinetic luminosity (${\dot{E}}_{k}\sim {10}^{43.6-44.8}$ erg s⁻¹) are then inferred jointly from the blueshifted emission and absorption lines. In the NIR spectrum of F11119+3257, we also find that the Paschen emission lines are unique, in which a very narrow (FWHM = 260 ± 20  km s⁻¹) component is shown in only Paα. This narrow component most probably comes from heavily obscured star formation. Based on the Paα and Paβ emissions, we obtain an extinction at the H band, A_H > 2.1 (or a reddenning of ${E}_{B-V}$ > 3.7), and a star formation rate of SFR > 130 M_⊙ yr⁻¹ that resembles the estimates inferred from the far-IR emissions (SFR_FIR = 190 ± 90 M_⊙ yr⁻¹).

The radius R_1.4 of neutron stars (NSs) with a mass of 1.4 M_⊙ has been extracted consistently in many recent studies in the literature. Using representative R_1.4 data, we infer high-density nuclear symmetry energy E_sym(ρ) and the associated nucleon specific energy E₀(ρ) in symmetric nuclear matter (SNM) within a Bayesian statistical approach using an explicitly isospin-dependent parametric equation of state (EOS) for nucleonic matter. We found the following. (1) The available astrophysical data can already significantly improve our current knowledge about the EOS in the density range of ρ₀ − 2.5ρ₀. In particular, the symmetry energy at twice the saturation density ρ₀ of nuclear matter is determined to be E_sym(2ρ₀)=${39.2}_{-8.2}^{+12.1}$ MeV at a 68% confidence level. (2) A precise measurement of R_1.4 alone with a 4% 1σ statistical error but no systematic error will not greatly improve the constraints on the EOS of dense neutron-rich nucleonic matter compared to what we extracted from using the available radius data. (3) The R_1.4 radius data and other general conditions, such as the observed NS maximum mass and causality condition, introduce strong correlations for the high-order EOS parameters. Consequently, the high-density behavior of E_sym(ρ) inferred depends strongly on how the high-density SNM EOS E₀(ρ) is parameterized, and vice versa. (4) The value of the observed maximum NS mass and whether it is used as a sharp cutoff for the minimum maximum mass or through a Gaussian distribution significantly affects the lower boundaries of both E₀(ρ) and E_sym(ρ) only at densities higher than about 2.5ρ₀.

We present the first release of the MaNGA Stellar Library (MaStar), which is a large, well-calibrated, high-quality empirical library covering the wavelength range 3622–10354 Å at a resolving power of R ∼ 1800. The spectra were obtained using the same instrument as used by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, by piggybacking on the Sloan Digital Sky Survey (SDSS-IV)/Apache Point Observatory Galaxy Evolution Experiment 2-N (APOGEE-2N) observations. Compared to previous empirical libraries, the MaStar library will have a higher number of stars and a more comprehensive stellar-parameter coverage, especially of cool dwarfs, low-metallicity stars, and stars with different [α/Fe], achieved by a sophisticated target-selection strategy that takes advantage of stellar-parameter catalogs from the literature. This empirical library will provide a new basis for stellar-population synthesis and is particularly well suited for stellar-population analysis of MaNGA galaxies. The first version of the library contains 8646 high-quality per-visit spectra for 3321 unique stars. Compared to photometry, the relative flux calibration of the library is accurate to 3.9% in g − r, 2.7% in r − i, and 2.2% in i − z. The data are released as part of SDSS Data Release 15. We expect the final release of the library to contain more than 10,000 stars.

We present a novel study of dust-vortex evolution in global two-fluid disk simulations to find out if evolution toward high dust-to-gas ratios can occur in a regime of well-coupled grains with low Stokes numbers (St = 10⁻³ − 4 × 10⁻²). We design a new implicit scheme in the code RoSSBi, to overcome the short time-steps occurring for small grain sizes. We discover that the linear capture phase occurs self-similarly for all grain sizes, with an intrinsic timescale (characterizing the vortex lifetime) scaling as 1/St. After vortex dissipation, the formation of a global active dust ring is a generic outcome confirming our previous results obtained for larger grains. We propose a scenario in which, regardless of grain size, multiple pathways can lead to local dust-to-gas ratios of about unity and above on relatively short timescales, <10⁵ yr, in the presence of a vortex, even with St = 10⁻³. When St > 10⁻², the vortex is quickly dissipated by two-fluid instabilities, and large dust density enhancements form in the global dust ring. When St < 10⁻², the vortex is resistant to destabilization. As a result, dust concentrations occur locally due to turbulence developing inside the vortex. Regardless of the Stokes number, dust-to-gas ratios in the range 1–10, a necessary condition to trigger a subsequent streaming instability, or even a direct gravitational instability of the dust clumps, appears to be an inevitable outcome. Although quantitative connections with other instabilities still need to be made, we argue that our results support a new scenario of vortex-driven planetesimal formation.

We explore the structure of the element abundance–age–orbit distribution of the stars in the Milky Way's low-α disk, by (re-)deriving precise [Fe/H], [X/Fe], and ages, along with orbits, for red clump stars from the apogee survey. There has been a long-standing theoretical expectation and observational evidence that metallicity ([Fe/H]) and age are informative about a star's orbit, e.g., about its angular momentum and the corresponding mean Galactocentric distance or its vertical motion. Indeed, our analysis of the apogee data confirms that [Fe/H] or age alone can predict the stars' orbits far less well than a combination of the two. Remarkably, we find and show explicitly that, for known [Fe/H] and age, the other abundances [X/Fe] of Galactic disk stars can be predicted well (on average to 0.02 dex) across a wide range of Galactocentric radii, and therefore provide little additional information, e.g., for predicting their orbit. While the age–abundance space for metal-poor stars and potentially for stars near the Galactic center is rich or complex, for the bulk of the Galaxy's low-α disk it is simple: [Fe/H] and age contain most information, unless [X/Fe] can be measured to 0.02 or better. Consequently, we do not have the precision with current (and likely near-future) data to assign stars to their individual (coeval) birth clusters, from which the disk is presumably formed. We can, however, place strong constraints on future models of Galactic evolution, chemical enrichment, and mixing.

The relationship between a decaying plasma turbulence and proton fire hose instabilities in a slowly expanding plasma is investigated using three-dimensional hybrid expanding box simulations. We impose an initial ambient magnetic field along the radial direction, and we start with an isotropic spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations with zero cross-helicity. A turbulent cascade rapidly develops and leads to a weak proton heating that is not sufficient to overcome the expansion-driven perpendicular cooling. The plasma system eventually drives the parallel and oblique fire hose instabilities that generate quasi-monochromatic wave packets that reduce the proton temperature anisotropy. The fire hose wave activity has a low amplitude with wave vectors quasi-parallel/oblique with respect to the ambient magnetic field outside of the region dominated by the turbulent cascade and is discernible in one-dimensional power spectra taken only in the direction quasi-parallel/oblique with respect to the ambient magnetic field; at quasi-perpendicular angles the wave activity is hidden by the turbulent background. These waves are partly reabsorbed by protons and partly couple to and participate in the turbulent cascade. Their presence reduces kurtosis, a measure of intermittency, and the Shannon entropy, but increases the Jensen–Shannon complexity of magnetic fluctuations; these changes are weak and anisotropic with respect to the ambient magnetic field and it is not clear if they can be used to indirectly discern the presence of instability-driven waves.

This paper studies the effectiveness of production of Alfvén waves in the solar atmosphere through the processes of mode conversion, taking into account several new effects that have not been considered before. We perform simulations of wave propagation and conversion from the photosphere to the corona. Both magnetic field and plasma parameters are structured in the form of small-scale flux tubes with characteristic scale significantly below the wavelength of the waves. The waves are allowed to dissipate through the ambipolar diffusion (AD) mechanism. We use an analytical magneto-static equilibrium model, which provides the AD coefficient values at the lower end of what is expected for the quiet solar regions. This work extends the simplified study of mode conversion by Cally and Cally & Khomenko to the case of warm, partially ionized, and structured plasma. We conclude that interaction of waves with the flux tube ensemble produces a discrete spectrum of high-order harmonics. The scattering is a linear process: however, the nonlinear effects have considerable influence upon the amplitudes of the harmonics. The magnetic Poynting flux reaching the corona is enhanced by about 35% and the reflection of waves at the transition region is decreased by about 50% when the flux tubes structure is present, relative to the horizontally homogeneous case. The energy flux of Alfvén waves exceeds that of acoustic waves at coronal heights. Ambipolar diffusion decreases the magnetic Poynting flux in the corona because the fast waves entering the transformation region at chromospheric heights are degraded and have lower amplitudes. The effect of the enhancement of Alfvén wave production due to interaction with flux tubes is independent of the numerical resolution, while the effect of the AD is resolution-dependent and is not converged at the 10 km resolution of our best simulations.

We present the first subarcsecond images of 49 Ceti in the [C i] ³P₁–³P₀ emission and the 614 μm dust continuum emission observed with Atacama Large Millimeter/submillimeter Array (ALMA), as well as that in the CO(J = 3–2) emission prepared by using the ALMA archival data. The spatial distribution of the 614 μm dust continuum emission is found to have a broad-ring structure with a radius of about 100 au around the central star. A substantial amount of gas is also associated with 49 Ceti. The [C i] emission map shows two peaks inside the dust ring, and its overall extent is comparable to that of the dust continuum emission and the CO emission. We find that the [C i]/CO(J = 3–2) intensity ratio significantly varies along the major axis. The ratio takes the minimum value of 1.8 around the dust peak position, and increases inward and outward. The enhanced ratio around the central star (∼3) likely originates from the stellar UV radiation, while that in the outer disk (∼10) is from the interstellar UV radiation. Such complex distributions of the [C i] and CO(J = 3–2) emission will be key to understanding the origin of the gas in 49 Ceti, and will also provide a stringent constraint on physical and chemical models of gaseous debris disks.

We use the Wide Field Camera 3 on the Hubble Space Telescope to spectrophotometrically monitor the young L7.5 companion HD 203030B. Our time series reveal photometric variability at 1.27 and 1.39 μm on timescales compatible with rotation. We find a rotation period of ${7.5}_{-0.5}^{+0.6}$ hr: comparable to those observed in other brown dwarfs and planetary-mass companions younger than 300 Myr. We measure variability amplitudes of 1.1% ± 0.3% (1.27 μm) and 1.7% ± 0.4% (1.39 μm), and a phase lag of 56° ± 28° between the two light curves. We attribute the difference in photometric amplitudes and phases to a patchy cloud layer that is sinking below the level where water vapor becomes opaque. HD 203030B and the few other known variable young late-L dwarfs are unlike warmer (earlier-type and/or older) L dwarfs, for which variability is much less wavelength-dependent across the 1.1–1.7 μm region. We further suggest that a sinking of the top-most cloud deck below the level where water or carbon monoxide gas become opaque may also explain the often enhanced variability amplitudes of even earlier-type low-gravity L dwarfs. Because these condensate and gas opacity levels are already well-differentiated in T dwarfs, we do not expect the same variability amplitude enhancement in young versus old T dwarfs.

Stars spend most of their lifetimes on the "main sequence" (MS) in the Hertzsprung–Russell diagram. The obvious double MSs seen in the equivalent color–magnitude diagrams characteristic of Milky Way open clusters (OCs) pose a fundamental challenge to our traditional understanding of star clusters as "single stellar populations." The clear MS bifurcation of early-type stars with masses greater than ∼1.6 M_⊙ is thought to result from a range in the stellar rotation rates. However, direct evidence connecting double MSs to stellar rotation properties has yet to emerge. Here, we show through analysis of the projected stellar rotational velocities (v sin i, where i represents the star's inclination angle) that the well-separated double MS in the young, ∼200 Myr old Milky Way OC NGC 2287 is tightly correlated with a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster's member stars in stellar binary systems. We show that the slow rotators could potentially be initially rapidly rotating stars that have been slowed down by tidal locking by a low-mass-ratio companion in a cluster containing a large fraction of short-period, low-mass-ratio binaries. This demonstrates that stellar rotation drives the split MSs in young, ⪅300 Myr old star clusters. However, special conditions, e.g., as regards the mass-ratio distribution, might be required for this scenario to hold.

We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 [O iii] emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg², surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Lyα emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N vλ1240 emission and resembles that of lower-z narrow-line quasars, the small Lyα width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.

A few months ago, GRAVITY at the Very Large Telescope Interferometry revealed the structure and kinematics of the broad-line region (BLR) of 3C 273. GRAVITY works with an unprecedented high spatial resolution through spectroastrometry where centers of photons at different wavelengths (λ-photoncenters) of active galactic nuclei are measured by differential phase curves (DPCs) in the wavelength range of the broad Paschenα line. Since Doppler effects govern wavelength shifts of photons sensitively depending on the degree of the ordered rotation (${{ \mathcal R }}_{0}$) of clouds in the BLR, the DPCs are expected to be a function of ${{ \mathcal R }}_{0}$. Distributions of the angular momenta of clouds in the BLR could be determined by the formation processes of the BLR; however, ${{ \mathcal R }}_{0}$ is a totally unknown parameter so far. In this paper, we show that the DPC is sensitive to this free parameter, and ${{ \mathcal R }}_{0}$ should be taken into account for GRAVITY measurements of the BLR. It is then expected that joint observations of reverberation mapping campaigns and GRAVITY will allow us to obtain complete information about the structure and kinematics of the BLR, including the degree of ordered rotation of clouds, offering an opportunity to reveal the formation of the BLR, either from the tidal capture of clumps in the torus or from winds that developed from accretion disks.

The wave–particle cyclotron interaction is a basic process in collisionless plasmas, which results in the redistribution of the energy between plasma waves and charged particles. This paper presents an event observation in order to explore the dynamics of charged particles and plasma waves, i.e., mirror, electromagnetic ion cyclotron (EMIC), and whistler waves, in the Earth's magnetosheath. It shows that when ions have a high-speed streaming velocity parallel to the magnetic field, EMIC waves arise. We also find that the frequency distribution of nearly parallel and nearly antiparallel whistler waves depends on the parallel streaming velocity of electrons. Based on the linear kinetic theory and the fitting plasma parameters, we show that the differential flows among ion components can enhance the ion cyclotron anisotropy instability that is even stronger than the mirror instability. The differential electron flows induce an asymmetry of the growth rate of counter-propagating whistler waves in the electron cyclotron anisotropy instability. On the other hand, the low-frequency EMIC and transverse electromagnetic waves modulate the ion pitch angle distribution. Moreover, when charged particles flow across the magnetic field, both low- and high-energy electrons are deeply trapped by mirror waves. These results illustrate new features of the observed plasma waves and charged particles in the Earth's magnetosheath, which could inspire improvement of the wave models therein.

We present the results of spectroscopic observations and Hα Doppler tomography of the massive close binary system UU Cas where a giant star fills its Roche lobe (donor) and transfers material through the vicinity of the L₁ point onto a massive but rather compact stellar companion (accretor). The system has been observed at the 1.2 m telescope of the Kourovka Astronomical Observatory. By analyzing the obtained spectra and computed Doppler tomogram, we suggest that at least three elements of the gas dynamic pattern in the system contribute to the Balmer Hα emission line profiles. These elements are: the stream from the L₁ point, the stellar wind from the accretor, and the diffuse disk, surrounding the accretor. In combination with the estimates of the companions' masses, our findings indicate that the system is at the late stage of the first mass transfer phase of its evolution.

The Lorentz factor of a relativistic jet and its evolution during the jet expansion are difficult to estimate, especially for the jets in gamma-ray bursts (GRBs). However, the Lorentz factor is related to the jet physics. Owing to the absorption of two-photon pair production ($\gamma \gamma \leftrightarrow {e}^{+}{e}^{-}$), a high-energy spectral cutoff may appear in the radiation spectrum of GRBs. We search for such high-energy cutoffs in GRB 160625B, which is one of the brightest bursts in recent years. It is found that the high-energy spectral cutoff is obvious for the first pulse in the second emission episode of GRB 160625B (i.e., ∼186–192 s after the burst first trigger), which is smooth and well-shaped. Then, we estimate the Lorentz factor and radiation location of the jet shell associated with the first pulse in the second emission episode of GRB 160625B. It is found that the radiation location increases with time. In addition, the Lorentz factor remains almost constant during the expansion of the jet shell. This reveals that the magnetization of the jet is low or intermediate in the emission region, even though the jet could still be Poynting-flux-dominated at smaller radii to avoid a bright thermal component in the emission episode.

Quantum interference effects, together with partial frequency redistribution (PFR) in line scattering, produce subtle signatures in the so-called Second Solar Spectrum (the linearly polarized spectrum of the Sun). These signatures are modified in the presence of arbitrary strength magnetic fields via the Hanle, Zeeman, and Paschen–Back effects. In the present paper we solve the problem of polarized line formation in a magnetized atmosphere taking into account scattering in a two-level atom with hyperfine structure splitting together with PFR. To this end we incorporate the collisionless PFR matrix derived in Sowmya et al. in the polarized transfer equation. We apply the scattering expansion method to solve this transfer equation. We study the combined effects of PFR and the Paschen–Back effect on polarized line profiles formed in an isothermal one-dimensional planar atmosphere. For this purpose, we consider the cases of D₂ lines of Li i and Na i.

We present results from multifrequency polarization-sensitive Very Large Array observations of the Seyfert–starburst composite galaxy NGC 3079. Our sensitive radio observations reveal a plethora of radio "filaments" comprising the radio lobes in this galaxy. We analyze the origin of these radio filaments in the context of existing Chandra X-ray and HST emission-line data. We do not find a one-to-one correlation of the radio filaments with the emission-line filaments. The northeastern lobe is highly polarized with polarization fractions ∼33% at 5 GHz. The magnetic fields are aligned with the linear extents of the optically thin filaments, as observed in our, as well as other, observations in the literature. Our rotation measure images show evidence for rotation measure inversion in the northeastern lobe. Our data best fit a model where the cosmic rays follow the magnetic field lines generated as a result of the dynamo mechanism. There could be additional effects like shock acceleration that might also be playing a role. We speculate that the peculiar radio lobe morphology is a result of an interplay between both the superwinds and the active galactic nucleus jet that are present in the galaxy. The jet, in fact, might be playing a major role in providing the relativistic electron population that is present in the radio lobes.

We utilize a modified astrochemistry code that includes cosmic-ray (CR) attenuation in situ to quantify the impact of different CR models on the CO-to-H₂ and CI-to-H₂ conversion factors, X_CO and X_CI, respectively. We consider the impact of CRs accelerated by accretion shocks, and show that clouds with star formation efficiencies greater than 2% have X_CO = (2.5 ± 1) × 10²⁰ cm⁻²(K km s⁻¹)⁻¹, consistent with Milky Way observations. We find that changing the CR ionization rate from external sources from the canonical ζ ≈ 10⁻¹⁷ to ζ ≈ 10⁻¹⁶ s⁻¹, which better represents observations in diffuse gas, reduces X_CO by 0.2 dex for clusters with surface densities below 3 g cm⁻². We show that embedded sources regulate X_CO and decrease its variance across a wide range of surface densities and star formation efficiencies. Our models reproduce the trends of a decreased X_CO in extreme CR environments. X_CI has been proposed as an alternative to X_CO due to its brightness at high redshifts. The inclusion of internal CR sources leads to 1.2 dex dispersion in X_CI ranging from 2 × 10²⁰ < X_CI < 4 × 10²¹ cm⁻² (K km s⁻¹)⁻¹. We show that X_CI is highly sensitive to the underlying CR model.

Within the binary-driven hypernova I (BdHN I) scenario, the gamma-ray burst GRB190114C originates in a binary system composed of a massive carbon–oxygen core (CO_core), and a binary neutron star (NS) companion. As the CO_core undergoes a supernova explosion with the creation of a new neutron star (νNS), hypercritical accretion occurs on the companion binary neutron star until it exceeds the critical mass for gravitational collapse. The formation of a black hole (BH) captures 10⁵⁷ baryons by enclosing them within its horizon, and thus a cavity of approximately 10¹¹ cm is formed around it with initial density 10⁻⁷ g cm⁻³. A further depletion of baryons in the cavity originates from the expansion of the electron-positron-photon (e⁺e⁻γ) plasma formed at the collapse, reaching a density of 10⁻¹⁴ g cm⁻³ by the end of the interaction. It is demonstrated here using an analytical model complemented by a hydrodynamical numerical simulation that part of the e⁺e⁻γ plasma is reflected off the walls of the cavity. The consequent outflow and its observed properties are shown to coincide with the featureless emission occurring in a time interval of duration t_rf, measured in the rest frame of the source, between 11 and 20 s of the GBM observation. Moreover, similar features of the GRB light curve were previously observed in GRB 090926A and GRB 130427A, all belonging to the BdHN I class. This interpretation supports the general conceptual framework presented in R. Ruffini et al. and guarantees that a low baryon density is reached in the cavity, a necessary condition for the operation of the "inner engine" of the GRB presented in an accompanying article.

The streaming instability concentrates solid particles in protoplanetary disks, leading to gravitational collapse into planetesimals. Despite its key role in producing particle clumping and determining critical length scales in the instability's linear regime, the influence of the disk's radial pressure gradient on planetesimal properties has not been examined in detail. Here, we use streaming instability simulations that include particle self-gravity to study how the planetesimal initial mass function depends on the radial pressure gradient. Fitting our results to a power law, ${dN}/{{dM}}_{p}\propto {M}_{p}^{-p}$, we find that a single value p ≈ 1.6 describes simulations in which the pressure gradient varies by ≳2. An exponentially truncated power law provides a significantly better fit, with a low-mass slope of p' ≈ 1.3 that weakly depends on the pressure gradient. The characteristic truncation mass is found to be $\sim {M}_{G}=4{\pi }^{5}{G}^{2}{{\rm{\Sigma }}}_{p}^{3}/{{\rm{\Omega }}}^{4}$. We exclude the cubic dependence of the characteristic mass with pressure gradient suggested by linear considerations, finding instead a linear scaling. These results strengthen the case for a streaming-derived initial mass function that depends at most weakly on the aerodynamic properties of the disk and participating solids. A simulation initialized with zero pressure gradient—which is not subject to the streaming instability—also yields a top-heavy mass function but with modest evidence for a different shape. We discuss the consistency of the theoretically predicted mass function with observations of Kuiper Belt planetesimals, and describe implications for models of early-stage planet formation.

We present observations using the Atacama Large Millimeter/submillimeter Array of the CO(2−1), HCN(3−2), and HCO⁺(3−2) lines in the nearby radio galaxy/brightest cluster galaxy (BCG) NGC 1275 with a spatial resolution of ∼20 pc. In previous observations, the CO(2−1) emission was detected as radial filaments lying in the east–west direction on a kiloparsec scale. We resolved the inner filament and found that it cannot be represented by a simple infalling stream on a sub-kiloparsec scale. The observed complex nature of the filament resembles the cold gas structure predicted by numerical simulations of cold chaotic accretion. Within the central 100 pc, we detected a rotational disk of molecular gas whose mass is ∼10⁸M_⊙. This is the first evidence of the presence of a massive cold gas disk on this spatial scale for BCGs. A crude estimate suggests that the accretion rate of the cold gas can be higher than that of hot gas. The disk rotation axis is approximately consistent with the radio-jet axis. This probably suggests that the cold gas disk is physically connected to the innermost accretion disk, which is responsible for jet launching. We also detected absorption features in the HCN(3−2) and HCO⁺(3−2) spectra against the radio continuum emission mostly radiated by a jet of size ∼1.2 pc. The absorption features are blueshifted from the systemic velocity by ∼300–600 km s⁻¹, suggesting the presence of outflowing gas from the active galactic nucleus (AGN). We discuss the relation of the AGN feeding with cold accretion, the origin of blueshifted absorption, and an estimate of the black hole mass using molecular gas dynamics.

Almost all planetary atmospheres are affected by disequilibrium chemical processes. In this paper, we introduce our recently developed chemical kinetic model (ChemKM). We show that the results of our HD 189733b model are in good agreement with previously published results, except at the μbar regime, where molecular diffusion and photochemistry are the dominant processes. We thus recommend careful consideration of these processes when abundances at the top of the atmosphere are desired. We also propose a new metric for a quantitative measure of quenching levels. By applying this metric, we find that quenching pressure decreases with the effective temperature of planets, but it also varies significantly with other atmospheric parameters such as [Fe/H], log(g), and C/O. In addition, we find that the "methane valley," a region between 800 and 1500 K where above a certain C/O threshold value a greater chance of CH₄ detection is expected, still exists after including the vertical mixing. The first robust CH₄ detection on an irradiated planet (HD 102195b) places this object within this region, supporting our prediction. We also investigate the detectability of disequilibrium spectral fingerprints by the James Webb Space Telescope and suggest focusing on the targets with T_eff between 1000 and 1800 K, orbiting around M dwarfs, and having low surface gravity but high metallicity and a C/O ratio value around unity. Finally, constructing Spitzer color maps suggests that the main two color populations are largely insensitive to the vertical mixing. Therefore, any deviation of observational points from these populations is likely due to the presence of clouds and not disequilibrium processes. However, some cold planets (T_eff < 900 K) with very low C/O ratios (<0.25) show significant deviations, making these planets interesting cases for further investigation.

Surface granulation can be predicted with the mass, metallicity, and frequency of maximum oscillation power of a star. Using the orders-of-magnitude larger Apache Point Observatory Galaxy Evolution Experiment-Kepler (APOGEE-Kepler) sample, we recalibrate the relationship fit by Corsaro et al. for "flicker," an easier-to-compute diagnostic of this granulation. We find that the relationship between the stellar parameters and flicker is significantly different for dwarf and subgiant stars than it is for red giants. We also confirm a dependence of flicker amplitude on metallicity as seen originally by Corsaro et al., although the dependence found here is somewhat weaker. Using the same APOGEE-Kepler sample, we demonstrate that spectroscopic measurements alone provide sufficient information to estimate the flicker amplitude to 7% for giants, and 20% for dwarfs and subgiants. We provide a relationship that depends on effective temperature, surface gravity, and metallicity, and calculate predicted flicker values for 129,000 stars with APOGEE spectra. Finally, we use published relationships between flicker and radial velocity jitter to estimate minimum jitter values for these same 129,000 stars, and we identify stars whose total jitter is likely to be even larger than the granulation-driven jitter by virtue of large-amplitude photometric variability.

We study the extreme-ultraviolet (EUV) emissions modulated by leaky fast sausage modes (FSMs) in solar active region (AR) loops and examine their observational signatures via spectrometers like the EUV imaging spectrometer (EIS). After computing fluid variables of leaky FSMs with magnetohydrodynamic (MHD) simulations, we forward-model the intensity and spectral properties of the Fe x 185 Å and Fe xii 195 Å lines by incorporating nonequilibrium ionization (NEI) in the computations of the relevant ionic fractions. The damping times derived from the intensity variations are then compared with the wave values, namely, the damping times directly found from our MHD simulations. Our results show that in the equilibrium ionization cases, the density variations and the intensity variations can be either in phase or in antiphase, depending on the loop temperature. NEI considerably impacts the intensity variations but has only marginal effects on the derived Doppler velocity or Doppler width. We find that the damping time derived from the intensity can largely reflect the wave damping time if the loop temperature is not drastically different from the nominal formation temperature of the corresponding emission line. These results are helpful for understanding the modulations to the EUV emissions by leaky FSMs and hence helpful for identifying FSMs in solar AR loops.

Young stars emit strong flares of X-ray radiation that penetrate the surface layers of their associated protoplanetary disks. It is still an open question as to whether flares create significant changes in disk chemical composition. We present models of the time-evolving chemistry of gas-phase H₂O during X-ray flaring events. The chemistry is modeled at point locations in the disk between 1 and 50 au at vertical heights ranging from the midplane to the surface. We find that strong, rare flares, i.e., those that increase the unattenuated X-ray ionization rate by a factor of 100 every few years, can temporarily increase the gas-phase H₂O abundance relative to H by more than a factor of ∼3–5 along the disk surface (Z/R ≥ 0.3). We report that a "typical" flare, i.e., those that increase the unattenuated X-ray ionization rate by a factor of a few every few weeks, will not lead to significant, observable changes. Dissociative recombination of H₃O⁺, H₂O adsorption and desorption onto dust grains, and ultraviolet photolysis of H₂O and related species are found to be the three dominant processes regulating the gas-phase H₂O abundance. While the changes are found to be significant, we find that the effect on gas-phase water abundances throughout the disk is short-lived (days). Even though we do not see a substantial increase in long-term water (gas and ice) production, the flares' large effects may be detectable as time-varying inner disk water "bursts" at radii between 5 and 30 au with future far-infrared observations.

MAXI J1535−571 is a Galactic black hole candidate X-ray binary that was discovered going into outburst in 2017 September. In this paper, we present comprehensive radio monitoring of this system using the Australia Telescope Compact Array, as well as the MeerKAT radio observatory, showing the evolution of the radio jet during its outburst. Our radio observations show the early rise and subsequent quenching of the compact jet as the outburst brightened and then evolved toward the soft state. We constrain the compact jet quenching factor to be more than 3.5 orders of magnitude. We also detected and tracked (for 303 days) a discrete, relativistically moving jet knot that was launched from the system. From the motion of the apparently superluminal knot, we constrain the jet inclination (at the time of ejection) and speed to ≤45° and ≥0.69 c, respectively. Extrapolating its motion back in time, our results suggest that the jet knot was ejected close in time to the transition from the hard intermediate state to soft intermediate state. The launching event also occurred contemporaneously with a short increase in X-ray count rate, a rapid drop in the strength of the X-ray variability, and a change in the type-C quasi-periodic oscillation (QPO) frequency that occurs >2.5 days before the first appearance of a possible type-B QPO.

We present the high time resolution in situ observations of Langmuir waves, likely excited by an electron beam accelerated by a coronal-mass ejection-driven super-critical quasi-perpendicular interplanetary shock into its upstream solar wind, which happens to be the source region of a solar type II radio burst. We show that (1) these waves occur as coherent localized magnetic-field-aligned, one-dimensional wave packets with durations of a few milliseconds and with peak intensities well in excess of the threshold for strong turbulence processes, (2) they provide what is believed to be the first evidence for: (a) the oscillating two-stream instability (OTSI) ${L}_{1}+{L}_{2}\mathop{\longrightarrow }\limits^{S}U+D$, where L₁ and L₂, U and D, and S are the pump Langmuir waves, up- and down-shifted side bands, and ion sound waves, respectively, (b) a three-wave interaction $U+D\longrightarrow {T}_{2{f}_{\mathrm{pe}}}$, where ${T}_{2{f}_{\mathrm{pe}}}$ is the second-harmonic electromagnetic wave, (3) they satisfy the threshold condition for formation of collapsing solitons, and (4) they are accompanied by their ponderomotive force induced density cavities with $\tfrac{\delta {n}_{p}}{{n}_{e}}\gt \tfrac{\delta {n}_{b}}{{n}_{e}}$, where $\tfrac{\delta {n}_{p}}{{n}_{e}}$ is the level of ponderomotive force induced density fluctuations and $\tfrac{\delta {n}_{b}}{{n}_{e}}$ is that of the ambient fluctuations. These findings strongly suggest that the observed wave packets provide evidence for the collapsing solitons formed as a result of OTSI. The implication is that the strong turbulence processes probably play very important roles in excitation of type II radio emissions as well as in stabilization of shock-accelerated electron beams.

The velocity distribution function (VDF) of ions in the solar wind, as observed by spacecraft at 1 au and elsewhere in the heliosphere, exhibits a consistent trend: at low energies in the solar wind frame, the distribution is largely Maxwellian—the core; at higher but still modest energies in the solar wind frame, the distribution follows a power law (f ∝ v^−γ, where f is the VDF, v is the speed in the solar wind frame, and γ is an arbitrary spectral index parameter)—the tail—with a spectral index of γ ≈ 5 being extremely common. Several theories have been proposed to explain this common index. Among these theories is that the tail is a natural consequence of an ensemble of particles obeying Coulomb's law. In this study, we derive a general analytical formula for the distribution of electric fields, and find that it always exhibits a power-law tail with a spectral index of exactly 9/2, or 4.5, due to the spatial power-law index of Coulomb's law. We then show how the VDF is a convolution of the distribution of electric fields with a preexisting VDF, and that for small values of time after being created, the ion VDF always exhibits a γ = 9/2 power law, wherein the probability of the tail relative to the core depends on particle density, n, and inversely on the preexisting VDF thermal speed, v_th. Finally, we compare our results with previous works, and find good agreement but with important distinctions.

A longstanding problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and submillimeter regions of the sulfur-containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its b-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high-mass star-forming regions, however, resulted in nondetections. An analogous search for the lowest-energy isomer, ${{\rm{H}}}_{2}\mathrm{CCS}$, is presented for comparison, and also resulted in nondetections. Typical upper limits on the abundance of both species relative to hydrogen are 10⁻⁹–10⁻¹⁰. We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available.

The chemical structure of high-mass star nurseries is important for a general understanding of star formation. Deuteration is a key chemical process in the earliest stages of star formation because its efficiency is sensitive to the environment. Using the IRAM-30 m telescope at 1.3–4.3 mm wavelengths, we have imaged two parsec-scale high-mass protostellar clumps (P1 and S) that show different evolutionary stages but are located in the same giant filamentary infrared dark cloud G28.34+0.06. Deep spectral images at subparsec resolution reveal the dust and gas physical structures of both clumps. We find that (1) the low-J lines of N₂H⁺, HCN, HNC, and HCO⁺ isotopologues are subthermally excited; and (2) the deuteration of N₂H⁺ is more efficient than that of HCO⁺, HCN, and HNC by an order of magnitude. The deuterations of these species are enriched toward the chemically younger clump S compared with P1, indicating that this process favors the colder and denser environment (T_kin ∼ 14 K, N(NH₃) ∼ 9 × 10¹⁵ cm⁻²). In contrast, single deuteration of NH₃ is insensitive to the environmental difference between P1 and S; and (3) single deuteration of CH₃OH (>10%) is detected toward the location where CO shows a depletion of ∼10. This comparative chemical study between P1 and S links the chemical variations to the environmental differences and shows chemical similarities between the early phases of high- and low-mass star-forming regions.

The Chinese Space Station Optical Survey (CSS-OS) is a planned full sky survey operated by the Chinese Space Station Telescope (CSST). It can simultaneously perform the photometric imaging and spectroscopic slitless surveys, and will probe weak and strong gravitational lensing, galaxy clustering, individual galaxies and galaxy clusters, active galactic nucleus, and so on. It aims to explore the properties of dark matter and dark energy and other important cosmological problems. In this work, we focus on two main CSS-OS scientific goals, i.e., the weak gravitational lensing (WL) and galaxy clustering surveys. We generate the mock CSS-OS data based on the observational COSMOS and zCOSMOS catalogs. We investigate the constraints on the cosmological parameters from the CSS-OS using the Markov Chain Monte Carlo method. The intrinsic alignments, galaxy bias, velocity dispersion, and systematics from instrumental effects in the CSST WL and galaxy clustering surveys are also included, and their impacts on the constraint results are discussed. We find that the CSS-OS can improve the constraints on the cosmological parameters by a factor of a few (even one order of magnitude in the optimistic case), compared to the current WL and galaxy clustering surveys. The constraints can be further enhanced when performing joint analysis with the WL, galaxy clustering, and galaxy–galaxy lensing data. Therefore, the CSS-OS is expected to be a powerful survey for exploring the universe. Since some assumptions may be still optimistic and simple, it is possible that the results from the real survey could be worse. We will study these issues in detail with the help of simulations in the future.

We analyze the multifrequency radio spectral properties of 41 6 GHz-detected Atacama Large Millimeter/submillimeter Array (ALMA)-identified, submillimeter galaxies (SMGs), observed at 610 MHz, 1.4 GHz, and 6 GHz with the Giant Metrewave Radio Telescope and the Very Large Array. Combining high-resolution (∼05) 6 GHz radio and ALMA 870 μm imaging (tracing rest frame ∼20 GHz, and ∼250 μm dust continuum), we study the far-infrared/radio correlation via the logarithmic flux ratio q_IR, measuring $\langle {q}_{\mathrm{IR}}\rangle =2.20\pm 0.06$ for our sample. We show that the high-frequency radio sizes of SMGs are ∼1.9 ± 0.4× (∼2–3 kpc) larger than those of the cool dust emission, and find evidence for a subset of our sources being extended on ∼10 kpc scales at 1.4 GHz. By combining radio flux densities measured at three frequencies, we can move beyond simple linear fits to the radio spectra of high-redshift star-forming galaxies, and search for spectral curvature, which has been observed in local starburst galaxies. At least a quarter (10/41) of our sample shows evidence of a spectral break, with a median $\langle {\alpha }_{610\,\mathrm{GHz}}^{1.4\,\mathrm{GHz}}\rangle =-0.60\pm 0.06$, but $\langle {\alpha }_{1.4\,\mathrm{GHz}}^{6\,\mathrm{GHz}}\rangle =-1.06\pm 0.04$—a high-frequency flux deficit relative to simple extrapolations from the low-frequency data. We explore this result within this subset of sources in the context of age-related synchrotron losses, showing that a combination of weak magnetic fields (B ∼ 35 μG) and young ages (t_SB ∼ 40–80 Myr) for the central starburst can reproduce the observed spectral break. Assuming these represent evolved (but ongoing) starbursts, and we are observing these systems roughly halfway through their current episode of star formation, this implies starburst durations of ≲100 Myr, in reasonable agreement with estimates derived via gas depletion timescales.

We present a volume-limited, spectroscopically verified sample of M7−L5 ultracool dwarfs (UCDs) within 25 pc. The sample contains 410 sources, of which 93% have trigonometric distance measurements (80% from Gaia DR2) and 81% have low-resolution (R ∼ 120), near-infrared (NIR) spectroscopy. We also present an additional list of 60 sources that may be M7−L5 dwarfs within 25 pc when distance or spectral-type uncertainties are taken into account. The spectra provide NIR spectral and gravity classifications, and we use these to identify young sources, red and blue J − K_S color outliers, and spectral binaries. We measure very low gravity and intermediate-gravity fractions of ${2.1}_{-0.8 \% }^{+0.9 \% }$ and ${7.8}_{-1.5 \% }^{+1.7 \% }$, respectively; fractions of red and blue color outliers of ${1.4}_{-0.5 \% }^{+0.6 \% }$ and ${3.6}_{-0.9 \% }^{+1.0 \% }$, respectively; and a spectral binary fraction of ${1.6}_{-0.5 \% }^{+0.5 \% }$. We present an updated luminosity function for M7−L5 dwarfs continuous across the hydrogen-burning limit that agrees with previous studies. We estimate our completeness to range between 69% and 80% when compared to an isotropic model. However, we find that the literature late-M sample is severely incomplete compared to L dwarfs, with completeness of ${62}_{-7 \% }^{+8 \% }$ and ${83}_{-9 \% }^{+10 \% }$, respectively. This incompleteness can be addressed with astrometric-based searches of UCDs with Gaia to identify objects previously missed by color- and magnitude-limited surveys.