Table of contents

We present the physical extent of [C ii] 158 μm line-emitting gas from 46 star-forming galaxies at z = 4–6 from the ALMA Large Program to INvestigate C ii at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C ii] line (${r}_{{\rm{e}},[{\rm{C}}{\rm\small{II}}]}$) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum (${r}_{{\rm{e}},\mathrm{UV}}$) from Hubble Space Telescope images. The effective radius ${r}_{{\rm{e}},[{\rm{C}}{\rm\small{II}}]}$ exceeds ${r}_{{\rm{e}},\mathrm{UV}}$ by factors of ∼2–3, and the ratio of ${r}_{{\rm{e}},[{\rm{C}}{\rm\small{II}}]}/{r}_{{\rm{e}},\mathrm{UV}}$ increases as a function of M_star. We do not find strong evidence that the [C ii] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ≃1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C ii] component over 10 kpc scales detected at 4.1σ–10.9σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C ii]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C ii] line structure have high star formation rate, high stellar mass (M_star), low Lyα equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Lyα line), as compared to galaxies without such extended [C ii] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C ii] line structures are ubiquitous to high-z star-forming galaxies.

We report distinctive core profiles in the strongest optical helium line, He iλ5876, from high-resolution high-sensitivity observations of spectral type DB white dwarfs. By analyzing a sample of 40 stars from Keck/HIRES and VLT/UVES, we find the core appearance to be related to the degree of hydrogen and heavy element content in the atmosphere. New Ca K-line measurements or upper limits are reported for about half the sample stars. He iλ5876 emission cores with a self-reversed central component are present for those stars with relatively low hydrogen abundance, as well as relatively low atmospheric heavy element pollution. This self-reversed structure disappears for stars with higher degrees of pollution and/or hydrogen abundance, giving way to a single absorption core. From our model atmospheres, we show that the self-reversed emission cores can be explained by temperature inversions in the upper atmosphere. We propose that the transition to a single absorption core is due to the additional opacity from hydrogen and heavy elements that inhibits the temperature inversions. Our current models do not exactly match the effective temperature range of the phenomenon or the amplitude of the self-reversed structure, which is possibly a result of missing physics such as 3D treatment, convective overshoot, and/or non-LTE effects. The He iλ5876 line structure may prove to be a useful new diagnostic for calibrating temperature profiles in DB atmosphere models.

We study the mass fallback rate of tidally disrupted stars on marginally bound and unbound orbits around a supermassive black hole (SMBH) by performing three-dimensional smoothed particle hydrodynamic simulations with three key parameters. The star is modeled by a polytrope with two different indexes (n = 1.5 and 3). The stellar orbital properties are characterized by five orbital eccentricities ranging from e = 0.98 to 1.02, and five different penetration factors ranging from β = 1 to 3, where β represents the ratio of the tidal disruption to pericenter distance radii. We derive analytic formulae for the mass fallback rate as a function of the stellar density profile, orbital eccentricity, and penetration factor. Moreover, two critical eccentricities to classify tidal disruption events (TDEs) into five different types: eccentric ($e\lt {e}_{\mathrm{crit},1}$), marginally eccentric (${e}_{\mathrm{crit},1}\lesssim e\lt 1$), purely parabolic (e = 1), marginally hyperbolic ($1\lt e\lt {e}_{\mathrm{crit},2}$), and hyperbolic ($e\gtrsim {e}_{\mathrm{crit},2}$) TDEs, are reevaluated as ${e}_{\mathrm{crit},1}=1-2{q}^{-1/3}{\beta }^{k-1}$ and ${e}_{\mathrm{crit},2}=1+2{q}^{-1/3}{\beta }^{k-1}$, where q is the ratio of the SMBH to stellar masses and 0 < k ≲ 2. We find the asymptotic slope of the mass fallback rate varies with the TDE type. The asymptotic slope approaches −5/3 for the parabolic TDEs, is steeper for the marginally eccentric TDEs, and is flatter for the marginally hyperbolic TDEs. For the marginally eccentric TDEs, the peak of mass fallback rates can be about one order of magnitude larger than the parabolic TDE case. For marginally hyperbolic TDEs, the mass fallback rates can be much lower than the Eddington accretion rate, which can lead to the formation of a radiatively inefficient accretion flow, while hyperbolic TDEs lead to failed TDEs. Marginally unbound TDEs could be an origin of a very low-density gas disk around a dormant SMBH.

The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125,367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (apogee) DR14. We examine the ages and metallicities of 1654 bulge stars within ${R}_{\mathrm{GAL}}\lt 3.5\,\mathrm{kpc}$. We focus on fields with b < 12°, and out to longitudes of l < 15°. We see that stars in the bulge are about twice as old (τ = 8 Gyr), on average, compared to those in the solar neighborhood (τ = 4 Gyr), with a larger dispersion in [Fe/H] (≈0.38 compared to 0.23 dex). This age gradient comes primarily from the low-α stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] (σ_[Fe/H] ≈ 0.4 dex) and line-of-sight velocity (σ_vr ≈ 90 km s⁻¹), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of b = 8°, but not at b = 12°. Future apogee and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.

Quasars are the most luminous of active galactic nuclei, and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg² of the Stripe 82 field, of which the 15.6 deg² covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multiwavelength counterparts, and 30% of these are unobscured quasars, with L_X > 10⁴⁴ erg s⁻¹ and M_B < −23. We define a new population of quasars that are unobscured, have X-ray luminosities in excess of 10⁴⁴ erg s⁻¹, have broad emission lines, and yet are also bright in the far-infrared, with a 250 μm flux density of S₂₅₀ > 30 mJy. We refer to these Herschel-detected, unobscured quasars as "cold quasars." A mere 4% (21) of the X-ray- and optically selected unobscured quasars in Stripe 82X are detected at 250 μm. These cold quasars lie at z ∼ 1–3, have L_IR > 10¹²L_⊙, and have star formation rates (SFRs) of ∼200–1400 M_⊙ yr⁻¹. Cold quasars are bluer in the mid-IR than the full quasar population, and 72% of our cold quasars have WISE W3 < 11.5 [Vega], while only 19% of the full quasar sample meets this criteria. Crucially, cold quasars have on average ∼nine times as much star formation as the main sequence of star-forming galaxies at similar redshifts. Although dust-rich, unobscured quasars have occasionally been noted in the literature before, we argue that they should be considered as a separate class of quasars due to their high SFRs. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold quasars are type-1 blue quasars that reside in starburst galaxies.

We used the mark weighted correlation functions (MCFs), W(s), to study the large-scale structure of the universe. We studied five types of MCFs with the weighting scheme ρ^α, where ρ is the local density, and α is taken as −1, −0.5, 0, 0.5, and 1. We found that different MCFs have very different amplitudes and scale dependence. Some of the MCFs exhibit distinctive peaks and valleys that do not exist in the standard correlation functions. Their locations are robust against the redshifts and the background geometry; however, it is unlikely that they can be used as "standard rulers" to probe the cosmic expansion history. Nonetheless, we find that these features may be used to probe parameters related with the structure formation history, such as the values of σ₈ and the galaxy bias. Finally, after conducting a comprehensive analysis using the full shapes of the W(s)s and W_Δs(μ)s, we found that combining different types of MCFs can significantly improve the cosmological parameter constraints. Compared with using only the standard correlation function, the combinations of MCFs with α = 0, 0.5, 1 and α = 0, −1, −0.5, 0.5, 1 can improve the constraints on Ω_m and w by ≈30% and 50%, respectively. We find highly significant evidence that MCFs can improve cosmological parameter constraints.

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of four young, eruptive star–disk systems at 04 resolution: two FUors (V582 Aur and V900 Mon), one EXor (UZ Tau E), and one source with an ambiguous FU/EXor classification (GM Cha). The disks around GM Cha, V900 Mon, and UZ Tau E are resolved. These observations increase the sample of FU/EXors observed at subarcsecond resolution by 15%. The disk sizes and masses of FU/EXors objects observed by ALMA so far suggest that FUor disks are more massive than Class 0/I disks in Orion and Class II disks in Lupus of similar size. EXor disks in contrast do not seem to be distinguishable from these two populations. We reach similar conclusions when comparing the FU/EXor sample to the Class I and Class II disks in Ophiuchus. FUor disks around binaries are host to more compact disks than those in single-star systems, similar to noneruptive young disks. We detect a wide-angle outflow around GM Cha in ¹²CO emission, wider than typical Class I objects and more similar to those found around some FUor objects. We use radiative transfer models to fit the continuum and line data of the well-studied disk around UZ Tau E. The line data are well described by a Keplerian disk, with no evidence of outflow activity (similar to other EXors). The detection of wide-angle outflows in FUors but not in EXors support the current picture in which FUors are more likely to represent an accretion burst in the protostellar phase (Class I), while EXors are smaller accretion events in the protoplanetary (Class II) phase.

Metis, the space coronagraph on board the Solar Orbiter, offers us new capabilities for studying eruptive prominences and coronal mass ejections (CMEs). Its two spectral channels, hydrogen Lα and visible light (VL), will provide for the first time coaligned and cotemporal images to study dynamics and plasma properties of CMEs. Moreover, with the VL channel (580–640 nm) we find an exciting possibility to detect the helium D₃ line (587.73 nm) and its linear polarization. The aim of this study is to predict the diagnostic potential of this line regarding the CME thermal and magnetic structure. For a grid of models we first compute the intensity of the D₃ line together with VL continuum intensity due to Thomson scattering on core electrons. We show that the Metis VL channel will detect a mixture of both, with predominance of the helium emission at intermediate temperatures between 30 and 50,000 K. Then we use the code HAZEL to compute the degree of linear polarization detectable in the VL channel. This is a mixture of D₃ scattering polarization and continuum polarization. The former one is lowered in the presence of a magnetic field and the polarization axis is rotated (Hanle effect). Metis has the capability of measuring Q/I and U/I polarization degrees and we show their dependence on temperature and magnetic field. At T = 30,000 K we find a significant lowering of Q/I which is due to strongly enhanced D₃ line emission, while depolarization at 10 G amounts roughly to 10%.

Project AMIGA (Absorption Maps In the Gas of Andromeda) is a survey of the circumgalactic medium (CGM) of Andromeda (M31, ${R}_{\mathrm{vir}}$ ≃ 300 kpc) along 43 QSO sightlines at impact parameters 25 ≤ R ≤ 569 kpc (25 at R ≲ ${R}_{\mathrm{vir}}$). We use ultraviolet absorption measurements of Si ii, Si iii, Si iv, C ii, and C iv from the Hubble Space Telescope/Cosmic Origins Spectrograph and O vi from the Far Ultraviolet Spectroscopic Explorer to provide an unparalleled look at how the physical conditions and metals are distributed in the CGM of M31. We find that Si iii and O vi have a covering factor near unity for R ≲ 1.2 ${R}_{\mathrm{vir}}$ and ≲1.9 ${R}_{\mathrm{vir}}$, respectively, demonstrating that M31 has a very extended ∼10⁴–10^5.5 K ionized CGM. The metal and baryon masses of the 10⁴–10^5.5 K CGM gas within ${R}_{\mathrm{vir}}$ are ≳10⁸ and ≳4 × 10¹⁰ (Z/0.3 Z_⊙)⁻¹M_⊙, respectively. There is not much azimuthal variation in the column densities or kinematics, but there is with R. The CGM gas at R ≲ 0.5 ${R}_{\mathrm{vir}}$ is more dynamic and has more complicated, multiphase structures than at larger radii, perhaps a result of more direct impact of galactic feedback in the inner regions of the CGM. Several absorbers are projected spatially and kinematically close to M31 dwarf satellites, but we show that those are unlikely to give rise to the observed absorption. Cosmological zoom simulations of ∼L* galaxies have O vi extending well beyond ${R}_{\mathrm{vir}}$ as observed for M31 but do not reproduce well the radial column density profiles of the lower ions. However, some similar trends are also observed, such as the lower ions showing a larger dispersion in column density and stronger dependence on R than higher ions. Based on our findings, it is likely that the Milky Way has a ∼10⁴–10^5.5 K CGM as extended as for M31 and their CGM (especially the warm–hot gas probed by O vi) are overlapping.

The detection of the gamma-ray burst (GRB) X-ray emission line is important for studying GRB physics and constraining the GRB redshift. Since the line-like feature in the GRB X-ray spectrum was first reported in 1999, several works on line searching have been published over the past two decades. Even though some observations on the X-ray line-like feature were performed, its significance remains controversial to date. In this paper, we utilize the down-Comptonization mechanism and present the time evolution of the Fe Kα line emitted near the GRB central engine. The line intensity decreases with the evolution time, and the time evolution depends on the electron density and the electron temperature. In addition, the initial line with a larger broadening decreases less over time. For instance, when the emission line penetrates material with an electron density above 10¹² cm⁻³ at 1 keV, it generally becomes insignificant enough after 100 s for it not to be detected . The line-like profile deviates from the Gaussian form, and it finally changes to be similar to a blackbody shape at the time of the thermal equilibrium between the line photons and the surrounding material.

SN 2017eaw, the tenth supernova observed in NGC 6946, was a normal Type II-P supernova with an estimated 11–13 M_⊙ red supergiant progenitor. Here we present nebular-phase spectra of SN 2017eaw at +545 and +900 days post-max, extending approximately 50–400 days past the epochs of previously published spectra. While the +545 day spectrum is similar to spectra taken between days +400 and +493, the +900 day spectrum shows dramatic changes both in spectral features and emission-line profiles. The Hα emission is flat-topped and boxlike with sharp blue and red profile velocities of ≃−8000 and +7500 km s⁻¹. These late-time spectral changes indicate strong circumstellar interaction with a mass-loss shell, expelled ∼1700 yr before explosion. SN 2017eaw's +900 day spectrum is similar to those seen for SN 2004et and SN 2013ej observed 2–3 yr after explosion. We discuss the importance of late-time monitoring of bright SNe II-P and the nature of presupernova mass-loss events for SN II-P evolution.

We present a submillimeter continuum survey ("SCUBA2 High rEdshift bRight quasaR surveY," hereafter SHERRY) of 54 high-redshift quasars at 5.6 < z < 6.9 with quasar bolometric luminosities in the range of (0.2–5) × 10¹⁴L_⊙, using the Submillimetre Common-User Bolometer Array-2 (SCUBA2) on the James Clerk Maxwell Telescope. About 30% (16/54) of the sources are detected with a typical 850 μm rms sensitivity of 1.2 mJy beam⁻¹ (S_{ν,850 μm} = 4–5 mJy, at >3.5σ). The new SHERRY detections indicate far-infrared (FIR) luminosities of 3.5 × 10¹² to 1.4 × 10¹³L_⊙, implying extreme star formation rates of 90–1060 M_⊙ yr⁻¹ in the quasar host galaxies. Compared with z = 2–5 samples, the FIR-luminous quasars (L_FIR > 10¹³L_⊙) are rarer at z ∼ 6. The optical/near-infrared spectra of these objects show that 11% (6/54) of the sources have weak Lyα emission-line features, which may relate to different subphases of the central active galactic nuclei (AGNs). Our SCUBA2 survey confirms the trend reported in the literature that quasars with submillimeter detections tend to have weaker ultraviolet (UV) emission lines compared to quasars with nondetections. The connection between weak UV quasar line emission and bright dust continuum emission powered by massive star formation may suggest an early phase of AGN–galaxy evolution, in which the broad-line region is starting to develop slowly or is shielded from the central ionization source, and has unusual properties such as weak-line features or bright FIR emission.

The LIGO/Virgo Scientific Collaboration (LVC) recently announced the detection of a compact object binary merger, GW190425, with a total mass of ${3.4}_{-0.1}^{+0.3}$M_⊙ and individual component masses in the range of about 1.1–2.5 M_⊙. If the constituent compact objects are neutron stars, then the total mass is five standard deviations higher than the mean of 2.66 ± 0.12 M_⊙ for Galactic binary neutron stars. LVC suggests that the nondetection of such massive binary neutron star (BNS) systems in the Galaxy is due to a selection effect. However, we are unable to reconcile the inferred formation efficiency from the reported merger rate, ${{ \mathcal R }}_{\mathrm{GW}190425}={460}_{-390}^{+1050}$ yr⁻¹ Gpc⁻³, with predictions from our own study for fast-merging BNS systems. Moreover, the comparable merger rates of GW190425 and GW170817 are possibly in tension with our results for two reasons: (i) more massive systems are expected to have lower formation rates, and (ii) fast-merging channels should constitute ≲10% of the total BNS systems if case BB unstable mass transfer is permitted to take place as a formation pathway. We argue that, to account for the high merger rate of GW190425 as a BNS system, (i) our understanding of NS formation in supernova explosions must be revisited, or (ii) more massive NSs must be preferentially born with either very weak or very high magnetic fields so that they would be undetectable in the radio surveys. Perhaps the detected massive NSs in NS–white dwarf binaries are our clues to the formation path of GW190425 systems.

We use Gaia DR2 to hunt for runaway stars from the Orion Nebula Cluster (ONC). We search a region extending 45° around the ONC and out to 1 kpc to find sources that have overlapped in angular position with the cluster in the last ∼10 Myr. We find ∼17,000 runaway/walkaway candidates that satisfy this 2D traceback condition. Most of these are expected to be contaminants, e.g., caused by Galactic streaming motions of stars at different distances. We thus examine six further tests to help identify real runaways, namely: (1) possessing young stellar object (YSO) colors and magnitudes based on Gaia optical photometry; (2) having IR excess consistent with YSOs based on 2MASS and Wide-field Infrared Survey Explorer photometry; (3) having a high degree of optical variability; (4) having closest approach distances well-constrained to within the cluster half-mass radius; (5) having ejection directions that avoid the main Galactic streaming contamination zone; and (6) having a required radial velocity (RV) for 3D overlap of reasonable magnitude (or, for the 7% of candidates with measured RVs, satisfying 3D traceback). Thirteen sources, not previously noted as Orion members, pass all these tests, while another twelve are similarly promising, except they are in the main Galactic streaming contamination zone. Among these 25 ejection candidates, ten with measured RVs pass the most restrictive 3D traceback condition. We present full lists of runaway/walkaway candidates, estimate the high-velocity population ejected from the ONC, and discuss its implications for cluster formation theories via comparison with numerical simulations.

Wind-driven outflows are observed around a broad range of accreting objects throughout the universe, ranging from forming low-mass stars to supermassive black holes. We study the interaction between a central isotropic wind and an infalling, rotating envelope, which determines the steady-state cavity shape formed at their interface under the assumption of weak mixing. The shape of the resulting wind-blown cavity is elongated and self-similar, with a physical size determined by the ratio between wind ram pressure and envelope thermal pressure. We compute the growth of a warm turbulent mixing layer between the shocked wind and the deflected envelope, and calculate the resultant broad-line profile, under the assumption of a linear (Couette-type) velocity profile across the layer. We then test our model against the warm broad velocity component observed in CO J = 16–15 by Herschel/HIFI in the protostar Serpens-Main SMM1. Given independent observational constraints on the temperature and density of the dust envelope around SMM1, we find an excellent match to all its observed properties (line profile, momentum, temperature) and to the SMM1 outflow cavity width for a physically reasonable set of parameters: a ratio of wind to infall mass flux of ≃4%, a wind speed of v_w ≃ 30 km s⁻¹, an interstellar abundance of CO and H₂, and a turbulent entrainment efficiency consistent with laboratory experiments. The inferred ratio of ejection to disk accretion rate, ≃6%–20%, is in agreement with current disk wind theories. Thus, the model provides a new framework to reconcile the modest outflow cavity widths in protostars with large observed flow velocities. Being self-similar, it is applicable over a broader range of astrophysical contexts as well.

Depending on the stellar type, more than 15% of stars in the field have at least two stellar companions. Hierarchical triple systems can be assembled dynamically in dense star clusters, as a result of few-body encounters among stars and/or compact remnants in the cluster core. In this paper, we present the demographics of stellar and compact-object triples formed via binary–binary encounters in the CMC Cluster Catalog, a suite of cluster simulations with present-day properties representative of the globular clusters (GCs) observed in the Milky Way. We show how the initial properties of the host cluster set the typical orbital parameters and formation times of the formed triples. We find that a cluster typically assembles hundreds of triples with at least one black hole (BH) in the inner binary, while only clusters with sufficiently small virial radii are efficient in producing triples with no BHs. We show that a typical GC is expected to host tens of triples with at least one luminous component at present. We discuss how the Lidov–Kozai mechanism can drive the inner binary of these dynamically formed triples to high eccentricities, whenever it takes place before the triple is dynamically reprocessed by encountering another cluster member. Some of these systems can reach sufficiently large eccentricities to form a variety of transients and merger products, such as blue stragglers, X-ray binaries, Type Ia supernovae, Thorne–Zytkow objects, and gravitational wave sources.

Magnetic reconnection plays a crucial role in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bidirectional plasma outflows located within a large-scale plasma sheet observed in extreme-ultraviolet emission and scattered white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each of the bidirectional outflows originates in the plasma sheet from a discrete site, identified as a magnetic reconnection site. These reconnection sites reside at very low altitudes (<180 Mm, or 0.26 R_⊙) above the top of the flare arcade, a distance only <3% of the total length of a plasma sheet that extends to at least 10 R_⊙. Each arrival of sunward outflows at the loop-top region appears to coincide with an impulsive microwave and X-ray burst dominated by a hot source (10–20 MK) at the loop top and a nonthermal microwave burst located in the loop-leg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directed energy flux induces particle acceleration and plasma heating in the post-flare arcades, observed as the hot and nonthermal flare emissions.

Solar flares are 3D phenomena, but modeling a flare in 3D, including many of the important processes in the chromosphere, is a computational challenge. Accurately modeling the chromosphere is important, even if the transition region and corona are the areas of interest, due to the flow of energy, mass, and radiation through the interconnected layers. We present a solar flare arcade model that aims to bridge the gap between 1D and 3D modeling. Our approach is limited to the synthesis of optically thin emission. Using observed active region loop structures in a 3D domain, we graft simulated 1D flare atmospheres onto each loop, synthesize the emission, and then project that emission onto the 2D observational plane. Emission from SDO/AIA, GOES/XRS, and IRIS/SG Fe xxiλ1354.1 was forward modeled. We analyze the temperatures, durations, mass flows, and line widths associated with the flare, finding qualitative agreement but certain quantitative differences. Compared to observations, the Doppler shifts are of similar magnitude but decay too quickly. They are not as ordered, containing a larger amount of scatter compared to observations. The duration of gradual phase emission from GOES and AIA emission is also too short. Fe xxi lines are broadened, but not sufficiently. These findings suggest that additional physics is required in our model. The arcade model that we show here as a proof of concept can be extended to investigate other lines and global aspects of solar flares, providing a means to better test the coronal response to models of flare energy injection.

The solar magnetic activity cycle has an amplitude that varies within a wide but limited range of values. This implies that there are nonlinear mechanisms that prevent runaway solutions. The purpose of this paper is to propose observable nonlinear mechanisms in the framework of the Babcock–Leighton-type dynamo. Sunspot emergences show systematic properties that strong cycles tend to have higher mean latitudes and lower tilt angle coefficients. We use the surface flux transport model to investigate the effect of these systematic properties on the expected final total dipolar moment, i.e., cancellation plus generation of dipole moment by a whole solar cycle. We demonstrate that the systematic change in latitude has similar nonlinear feedback on the solar cycle (latitudinal quenching) as tilt does (tilt quenching). Both forms of quenching lead to the expected final total dipolar moment being enhanced for weak cycles and saturated to a nearly constant value for normal and strong cycles. This explains observed long-term solar cycle variability, e.g., the Gnevyshev–Ohl rule, which, in turn, justifies the nonlinear mechanisms inherent in the Babcock–Leighton-type dynamo.

The detailed magnetic field structure of the dense core SL 42 (CrA-E) in the Corona Australis molecular cloud complex was investigated based on near-infrared polarimetric observations of background stars to measure dichroically polarized light produced by magnetically aligned dust grains. The magnetic fields in and around SL 42 were mapped using 206 stars, and curved magnetic fields were identified. On the basis of simple hourglass (parabolic) magnetic field modeling, the magnetic axis of the core on the plane of the sky was estimated to be 40° ± 3°. The plane-of-sky magnetic field strength of SL 42 was found to be 22.4 ± 13.9 μG. Taking into account the effects of thermal/turbulent pressure and the plane-of-sky magnetic field component, the critical mass of SL 42 was obtained to be M_cr = 21.2 ± 6.6 M_⊙, which is close to the observed core mass of M_core ≈ 20 M_⊙. We thus conclude that SL 42 is in a condition close to the critical state if the magnetic fields lie near the plane of the sky. Because there is a very low-luminosity object toward the center of SL 42, it is unlikely that this core is in a highly subcritical condition (i.e., the magnetic inclination angle is significantly deviated from the plane of the sky). The core probably started to collapse from a nearly kinematically critical state. In addition to the hourglass magnetic field modeling, the Inoue & Fukui mechanism may explain the origin of the curved magnetic fields in the SL 42 region.

We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z ≃ 6 quasars and the z = 5.85 hot-dust-free quasar SDSS J0005–0006. We perform 2D surface brightness modeling for each quasar using a Markov Chain Monte Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of m_J > 22.7 mag and m_H > 22.4 mag, corresponding to stellar masses of M_* < 2 × 10¹¹M_⊙. These stellar mass limits are consistent with the local M_BH − M_* relation. Our flux limits are consistent with those predicted for the UV stellar populations of z ≃ 6 host galaxies, but likely in the presence of significant dust ($\langle {A}_{\mathrm{UV}}\rangle \simeq 2.6$ mag). We also detect a total of up to nine potential z ≃ 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 14–32, or 8.4–19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of −22.1 to −19.9 mag and UV spectral slopes β of −2.0 to −0.2, consistent with luminous star-forming galaxies at z ≃ 6. These results suggest that the quasars are in dense environments typical of luminous z ≃ 6 galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the z ≃ 6 quasar host galaxies and better constrain their stellar mass and dust content.

We report results from the analysis of XMM-Newton and INTEGRAL data of IGR J16479−4514. The unpublished XMM-Newton observation, performed in 2012, occurred during the source eclipse. No pointlike X-ray emission was detected from the source; conversely, extended X-ray emission was clearly detected up to a size distance compatible with a dust-scattering halo produced by the source X-ray emission before being eclipsed by its companion donor star. The diffuse emission of the dust-scattering halo could be observed without any contamination from the central point X-ray source, compared to a previous XMM-Newton observation published in 2008. Our comprehensive analysis of the 2012 unpublished spectrum of the diffuse emission, as well as the 2008 reanalyzed spectra extracted from three adjacent time intervals and different extraction regions (optimized for pointlike and extended emission), allowed us to clearly disentangle the scattering halo spectrum from the residual pointlike emission during the 2008 eclipse. Moreover, the pointlike emission detected in 2008 could be separated into two components attributed to the direct emission from the source and scattering in the stellar wind, respectively. From archival unpublished INTEGRAL data, we identified a very strong (∼3 × 10⁻⁸ erg cm⁻² s⁻¹) and fast (∼25 minute duration) flare that was classified as a giant hard X-ray flare, since the measured peak luminosity is ∼7 × 10³⁷ erg s⁻¹. Giant X-ray flares from supergiant fast X-ray transients are very rare; to date, only one has been reported from a different source. We propose a physical scenario to explain the origin in the case of IGR J16479−4514.

We present a multiwavelength analysis of two homologous, short-lived, impulsive flares of GOES class M1.4 and M7.3 that occurred from a very localized minisigmoid region within the active region NOAA 12673 on 2017 September 7. Both flares were associated with initial jetlike plasma ejection that for a brief amount of time moved toward the east in a collimated manner before drastically changing direction toward the southwest. Nonlinear force-free field extrapolation reveals the presence of a compact double-decker flux rope configuration in the minisigmoid region prior to the flares. A set of open field lines originating near the active region that were most likely responsible for the anomalous dynamics of the erupted plasma gave the earliest indication of an emerging coronal hole near the active region. The horizontal field distribution suggests a rapid decay of the field above the active region, implying high proneness of the flux rope system toward eruption. In view of the low coronal double-decker flux ropes and compact extreme ultraviolet brightening beneath the filament, along with associated photospheric magnetic field changes, our analysis supports the combination of initial tether-cutting reconnection and subsequent torus instability for driving the eruption.

The thermal, orbital, and rotational dynamics of tidally loaded exoplanets are interconnected by intricate feedback. The rheological structure of the planet determines its susceptibility to tidal deformation and, as a consequence, participates in shaping its orbit. The orbital parameters and the spin state, conversely, control the rate of tidal dissipation and may lead to substantial changes in the interior. We investigate the coupled thermal–orbital evolution of differentiated rocky exoplanets governed by the Andrade viscoelastic rheology. The coupled evolution is treated by a semianalytical model, 1D parameterized heat transfer, and self-consistently calculated tidal dissipation. First, we conduct several parametric studies, exploring the effect of the rheological properties, the planet size, and the orbital eccentricity on tidal locking and dissipation. These tests show that the role of tidal locking into high spin–orbit resonances is most prominent on low eccentric orbits, where it results in substantially higher tidal heating than synchronous rotation. Second, we calculate the long-term evolution of three currently known low-mass exoplanets with nonzero orbital eccentricity and absent or yet-unknown eccentricity forcing (namely GJ 625 b, GJ 411 b, and Proxima Centauri b). The tidal model incorporates the formation of a stable magma ocean and a consistently evolving spin rate. We find that the thermal state is strongly affected by the evolution of eccentricity and spin state and proceeds as a sequence of thermal equilibria. Final despinning into synchronous rotation slows down the orbital evolution and helps to maintain long-term stable orbital eccentricity.

We study the structure of accretion disks around supermassive black holes in the radial range of –100 gravitational radii, using a three-dimensional radiation magnetohydrodynamic simulation. For typical conditions in this region of active galactic nuclei (AGNs), the Rosseland mean opacity is expected to be larger than the electron scattering value. We show that the iron opacity bump causes the disk to be convectively unstable. Turbulence generated by convection puffs up the disk due to additional turbulent pressure support and enhances the local angular momentum transport. This also results in strong fluctuations in surface density and heating of the disk. The opacity drops with increasing temperature and convection is suppressed. The disk cools down and the whole process repeats again. This causes strong oscillations of the disk scale height and luminosity variations by more than a factor of ≈3–6 over a few years' timescale. Since the iron opacity bump will move to different locations of the disk for black holes with different masses and accretion rates, we suggest that this is a physical mechanism that can explain the variability of AGN with a wide range of amplitudes over a timescale of years to decades.

Using a nonlinear mean-field solar dynamo model, we study relationships between the amplitude of the "extended" mode of migrating zonal flows ("torsional oscillations") and magnetic cycles, and investigate whether properties the torsional oscillations in subsurface layers and in the deep convection zone can provide information about the future solar cycles. We consider two types of dynamo models: models with regular variations of the α-effect, and models with stochastic fluctuations, simulating "long-memory" and "short-memory" types of magnetic activity variations. It is found that torsional oscillation parameters, such the zonal acceleration, show a considerable correlation with the magnitude of the subsequent cycles with a time lag of 11–20 yr. The sign of the correlation and the time-lag parameters can depend on the depth and latitude of the torsional oscillations as well as on the properties of long-term ("centennial") variations of the dynamo cycles. The strongest correlations are found for the zonal acceleration at high latitudes at the base of the convection zone. The model results demonstrate that helioseismic observations of the torsional oscillations can be useful for advanced prediction of the solar cycles, 1–2 sunspot cycles ahead.

The nearby ultracool dwarf TRAPPIST-1 possesses several Earth-sized terrestrial planets, three of which have equilibrium temperatures that may support liquid surface water, making it a compelling target for exoplanet characterization. TRAPPIST-1 is an active star with frequent flaring, with implications for the habitability of its planets. Superflares (stellar flares whose energy exceeds 10³³ erg) can completely destroy the atmospheres of a cool star's planets, allowing ultraviolet radiation and high-energy particles to bombard their surfaces. However, ultracool dwarfs emit little ultraviolet flux when quiescent, raising the possibility of frequent flares being necessary for prebiotic chemistry that requires ultraviolet light. We combine Evryscope and Kepler observations to characterize the high-energy flare rate of TRAPPIST-1. The Evryscope is an array of 22 small telescopes imaging the entire Southern sky in g' every two minutes. Evryscope observations, spanning 170 nights over 2 yr, complement the 80 day continuous short-cadence K2 observations by sampling TRAPPIST-1's long-term flare activity. We update TRAPPIST-1's superflare rate, finding a cumulative rate of ${4.2}_{-0.2}^{+1.9}$ superflares per year. We calculate the flare rate necessary to deplete ozone in the habitable-zone planets' atmospheres, and find that TRAPPIST-1's flare rate is insufficient to deplete ozone if present on its planets. In addition, we calculate the flare rate needed to provide enough ultraviolet flux to power prebiotic chemistry. We find TRAPPIST-1's flare rate is likely insufficient to catalyze some of the Earthlike chemical pathways thought to lead to ribonucleic acid synthesis, and flux due to flares in the biologically relevant UV-B band is orders of magnitude less for any TRAPPIST-1 planet than has been experienced by Earth at any time in its history.

We present MINESweeper, a tool to measure stellar parameters by jointly fitting observed spectra and broadband photometry to model isochrones and spectral libraries. This approach enables the measurement of spectrophotometric distances, in addition to stellar parameters such as T_eff, $\mathrm{log}g$, [Fe/H], [α/Fe], and radial velocity. MINESweeper employs a Bayesian framework and can easily incorporate a variety of priors, including Gaia parallaxes. Mock data are fit in order to demonstrate how the precision of derived parameters depends on evolutionary phase and signal-to-noise ratio. We then fit a selection of data in order to validate the model outputs. Fits to a variety of benchmark stars including Procyon, Arcturus, and the Sun result in derived stellar parameters that are in good agreement with the literature. We then fit combined spectra and photometry of stars in the open and globular clusters M92, M13, M3, M107, M71, and M67. Derived distances, [Fe/H], [α/Fe], and $\mathrm{log}g$−T_eff relations are in overall good agreement with literature values, although there are trends between metallicity and $\mathrm{log}g$ within clusters that point to systematic uncertainties at the ≈0.1 dex level. Finally, we fit a large sample of stars from the H3 Spectroscopic Survey in which high-quality Gaia parallaxes are also available. These stars are fit without the Gaia parallaxes so that the geometric parallaxes can serve as an independent test of the spectrophotometric distances. Comparison between the two reveals good agreement within their formal uncertainties after accounting for the Gaia zero-point uncertainties.

We perform a priori validation tests of subgrid-scale (SGS) models for the turbulent transport of momentum, energy, and passive scalars. To this end, we conduct two sets of high-resolution hydrodynamical simulations with a Lagrangian code: an isothermal turbulent box with rms Mach numbers of 0.3, 2, and 8, and the classical wind tunnel where a cold cloud traveling through a hot medium gradually dissolves due to fluid instabilities. Two SGS models are examined: the eddy diffusivity (ED) model widely adopted in astrophysical simulations and the "gradient model" due to Clark et al. We find that both models predict the magnitude of the SGS terms equally well (correlation coefficient >0.8). However, the gradient model provides excellent predictions for the orientation and shape of the SGS terms while the ED model predicts both poorly, indicating that isotropic diffusion is a poor approximation to the instantaneous turbulent transport. The best-fit coefficient of the gradient model is in the range of [0.16, 0.21] for the momentum transport, and the turbulent Schmidt number and Prandtl number are both close to unity, in the range of [0.92, 1.15].

The impact of streaming between baryons and dark matter on the first structures has been actively explored by recent studies. We investigate how the key results are affected by two popular approximations. One is to implement the streaming by accounting for only the relative motion while assuming "baryons trace dark matter" spatially at the initialization of simulation. This neglects the smoothing on the gas density taking place before the initialization. In our simulation initialized at z_i = 200, it overestimates the gas density power spectrum by up to 40% at k ≈ 10²h Mpc⁻¹ at z = 20. Halo mass (M_h) and baryonic fraction in halos (${f}_{b,h}$) are also overestimated, but the relation between the two remains unchanged. The other approximation tested is to artificially amplify the density/velocity fluctuations in the cosmic mean density to simulate the first minihalos that form in overdense regions. This gives a head start to the halo growth while the subsequent growth is similar to that in the mean density. The growth in a true overdense region, on the other hand, is accelerated gradually in time. For example, raising σ₈ by 50% effectively transforms $z\to \sqrt{1.5}z$ in the halo mass growth history while, at 2σ overdensity, the growth is accelerated by a constant in redshift: $z\to z+4.8$. As a result, halos have grown more massive in the former than in the latter before z ≈ 27 and vice versa after. The ${f}_{b,h}$–M_h relation is unchanged in those cases as well, suggesting that the Population III formation rate for a given M_h is insensitive to the tested approximations.

The successful detection of the binary neutron star merger GW 170817 and its electromagnetic counterparts has provided an opportunity to explore the joint effect of the host galaxy and the Milky Way (MW) on the weak equivalence principle (WEP) test. In this paper, using the Navarro–Frenk–White profile and the Hernquist profile, we present an analytic model to calculate the galactic potential, in which the possible locations of the source from the observed angle offset and the second supernova kick are accounted for. We show that the upper limit of Δγ is 10⁻⁹ for the comparison between GW 170817 and a gamma-ray burst (GRB 170817A), and it is 10⁻⁴ for the comparison between GW 170817 and a bright optical transient (SSS 17a, now with the IAU identification of AT 2017gfo). These limits are more stringent by one to two orders of magnitude than those determined solely using the measured MW potential in the literature. We demonstrate that the WEP test is strengthened by the contribution from the host galaxy to the Shapiro time delay. Meanwhile, we also find that large natal kicks produce a maximum deviation of about 20% from the results with a typical kick velocity of 400 to ∼500 km s⁻¹. Finally, we analyze the impact from the halo mass of NGC 4993 with a typical 0.2 dex uncertainty and find that the upper limit of Δγ, with a maximum mass ${10}^{12.4}{h}^{-1}\,{M}_{\odot }$, is nearly two times more stringent than that of the minimum mass ${10}^{12.0}{h}^{-1}\,{M}_{\odot }$.

Nuclear star clusters (NSCs) are dense stellar clusters that are found at the centers of a majority of galaxies. In this paper, we study the density profiles for 29 galaxies in a volume-limited survey within 10 Mpc to characterize their NSCs. These galaxies span a 3 × 10⁸–8 × 10¹⁰M_⊙ and a wide range of Hubble types. We use high-resolution Hubble Space Telescope archival data to create luminosity models for the galaxies using Sérsic profiles to parameterize the NSCs. We also provide estimates for photometric masses of NSCs and their host galaxies using color–M/L relationships and examine their correlation. We use the multi-Gaussian expansion to derive the NSC densities and their 3D mass-density profiles. The 3D density profiles characterize the NSC densities on scales as small as ∼1 pc, approaching the likely spheres of influence for BHs in these objects. We find that these densities correlate with galaxy mass, with NSC density profiles becoming both denser and flatter at higher galaxy masses. Most galaxy NSCs are denser than typical globular clusters. We parameterize the 3D NSC density profiles and their scatter and slope as a function of galaxy stellar mass to enable the construction of realistic nuclear mass profiles. Our fitted profiles and the derived relations are useful in predicting the rate of tidal disruption events in galaxies. We will verify the results of this paper in a follow-up paper that presents the dynamical modeling of the same sample of NSCs.

The well-known Amati and Yonetoku relations in gamma-ray bursts show strong correlations between the rest-frame νf_ν spectrum peak energy, E_p,i, and the isotropic energy, E_iso, as well as isotropic peak luminosity, L_iso. Recently, Peng et al. showed that the cosmological rest-frame spectral widths are also correlated with E_iso and with L_iso. In this paper, we select a sample including 141 BEST time-integrated F spectra and 145 BEST peak flux P spectra observed by Konus–Wind with known redshift to recheck the connection between the spectral width and E_iso as well as L_iso. We define six types of absolute spectral widths as the differences between the upper (E₂) and lower energy bounds (E₁) of the full width at 50%, 75%, 85%, 90%, 95%, and 99% of maximum of the EF_E versus E spectra. It is found that all of the rest-frame absolute spectral widths are strongly positively correlated with E_iso as well as L_iso for the long burst for both the F and P spectra. All of the short bursts are outliers for the width–E_iso relation, and most of the short bursts are consistent with the long bursts for the width–L_iso relation for both F and P spectra. Moreover, all of the location energies, E₂ and E₁, corresponding to various spectral widths, are also positively correlated with E_iso as well as L_iso. We compare all of the relations with the Amati and Yonetoku relations and find that the width–E_iso and width–L_iso relations, when the widths are at about 90% maximum of the EF_E spectra, almost overlap with the Amati relation and the Yonetoku relation, respectively. The correlations of E₂ − E_iso, E₁ − E_iso and E₂ − L_iso, E₁ − L_iso when the location energies are at 99% of maximum of the EF_E spectra are very close to the Amati and Yonetoku relations, respectively. Therefore, we confirm the existence of tight width–E_iso and width–L_iso relations for long bursts. We further show that the spectral shape is indeed related to E_iso and L_iso. The Amati and Yonetoku relations are not necessarily the best relationships for relating the energy to the E_iso and L_iso. They may be special cases of the width–E_iso and width–L_iso relations or the energy–E_iso and energy–L_iso relations.

We study the potential of Lyman β and the O i 1027 and 1028 Å spectral lines to help in understanding the properties of the chromosphere and transition region (TR). The oxygen transitions are located in the wing of Lyman β, which is a candidate spectral line for the solar missions Solar Orbiter/Spectral Imaging of the Coronal Environment and Solar-C (EUVST). We examine the general spectroscopic properties of the three transitions in the quiet Sun by synthesizing them assuming nonlocal thermal equilibrium and taking into account partial redistribution effects. We estimate the heights where the spectral lines are sensitive to the physical parameters, computing the response functions to temperature and velocity using a 1D semiempirical atmospheric model. We also synthesize the intensity spectrum using the 3D enhanced network simulation computed with the Bifrost code. The results indicate that Lyman β is sensitive to the temperature from the middle chromosphere to the TR, while it is mainly sensitive to the line-of-sight (LOS) velocity at the lower atmospheric layers, around 2000 km above the optical surface. The O i  lines form lower in the middle chromosphere, being sensitive to the LOS velocities at heights lower than those covered by Lyman β. The spatial distribution of the intensity signals computed with the Bifrost atmosphere, as well as the inferred velocities from the line core Doppler shift, confirms the previous results. Therefore, these results indicate that the spectral window at 1025 Å contains several spectral lines that complement each other to seamlessly trace the thermal structure and gas dynamics from the middle chromosphere to the lower TR.

We introduce a new capability of the Neil Gehrels Swift Observatory to provide event-level data from the Burst Alert Telescope (BAT) on demand in response to transients detected by other instruments. We show that the availability of these data can effectively increase the rate of detections and arcminute localizations of gamma-ray bursts (GRB) like GRB 170817 by >400%. We describe an autonomous spacecraft-commanding pipeline purpose built to enable this science; to our knowledge, this is the first fully autonomous extremely low-latency commanding of a space telescope for scientific purposes. This pipeline has been successfully run in its complete form since 2020 January, and has resulted in the recovery of BAT event data for >800 externally triggered events to date (gravitational waves, GWs; neutrinos; GRBs triggered by other facilities; fast radio bursts; and very high-energy detections), now running with a success rate of ∼90%. We exemplify the utility of this new capability by using the resultant data to (1) set the most sensitive upper limits on prompt 1 s duration short GRB-like emission within ±15 s around the unmodeled GW burst candidate S200114f, and (2) provide an arcminute localization for short GRB 200325A and other bursts. We also show that using data from GUANO to localize GRBs discovered by other instruments, we can increase the net rate of arcminute-localized GRBs by 10%–20% per year. Along with the scientific yield of more sensitive searches for subthreshold GRBs, the new capabilities designed for this project will serve as the foundation for further automation and rapid target of opportunity capabilities for the Swift mission, and have implications for the design of future rapid-response space telescopes.

We present the results of high-resolution (R ≥ 30,000) optical and near-infrared (NIR) spectroscopic monitoring observations of an FU Orionis–type object (FUor), V960 Mon, which underwent an outburst in 2014 November. We have monitored this object with the Bohyunsan Optical Echelle Spectrograph and the Immersion GRating INfrared Spectrograph since 2014 December. Various features produced by a wind, disk, and outflow/jet were detected. The wind features varied over time and continually weakened after the outburst. We detected double-peaked line profiles in the optical and NIR, and the line widths tend to decrease with increasing wavelength, indicative of Keplerian disk rotation. The disk features in the optical and NIR spectra fit well with G-type and K-type stellar spectra convolved with a kernel to account for the maximum projected disk rotation velocities of about 40.3 ± 3.8 km s⁻¹ and 36.3 ± 3.9 km s⁻¹, respectively. We also report the detection of [S ii] and H₂ emission lines, which are jet/outflow tracers and rarely found in FUors.

In a multiwavelength survey of 13 quasars at 5.8 ≲ z ≲ 6.5, which were preselected to be potentially young, we find five objects with extremely small proximity zone sizes that may imply UV-luminous quasar lifetimes of ≲100,000 yr. Proximity zones are regions of enhanced transmitted flux in the vicinity of quasars that are sensitive to the quasars' lifetimes because the intergalactic gas has a finite response time to their radiation. We combine submillimeter observations from the Atacama Large Millimetre Array and the NOrthern Extended Millimeter Array, as well as deep optical and near-infrared spectra from the medium-resolution spectrograph on the Very Large Telescope and on the Keck telescopes, in order to identify and characterize these new young quasars, which provide valuable clues about the accretion behavior of supermassive black holes in the early universe and pose challenges on current black hole formation models to explain the rapid formation of billion-solar-mass black holes. We measure the quasars' systemic redshifts, black hole masses, Eddington ratios, emission-line luminosities, and star formation rates of their host galaxies. Combined with previous results, we estimate the fraction of young objects within the high-redshift quasar population at large to be 5% ≲ f_young ≲ 10%. One of the young objects, PSO J158–14, shows a very bright dust continuum flux (F_cont = 3.46 ± 0.02 mJy), indicating a highly starbursting host galaxy with a star formation rate of approximately 1420 M_⊙ yr⁻¹.

Increasing attention has recently been paid to solar flares exhibiting double-J-shaped ribbons in the lower solar atmosphere, in the context of extending the two-dimensional standard flare model to three dimensions, as motivated by the spatial correlation between photospheric current channels and flare ribbons. Here, we study the electric currents through the photospheric area swept by flare ribbons (termed the synthesized ribbon area (SRA)), with a sample of 71 two-ribbon flares, of which 36 are J-shaped. Electric currents flowing through one ribbon are highly correlated with those flowing through the other, and they therefore belong to the same current system. The nonneutrality factor of this current system is independent of the flare magnitude, implying that both direct and return currents participate in flares. J-shaped flares are distinct from non-J-shaped flares in the following ways: (1) electric-current densities within the J-shaped SRA are significantly smaller than those within the non-J-shaped SRA, but the J-shaped SRA and its associated magnetic flux is also significantly larger. (2) Electric currents through the SRA are positively correlated with the flare magnitude, but J-shaped flares show a stronger correlation than non-J-shaped flares. (3) The majority (75%) of J-shaped flares are eruptive, while the majority (86%) of non-J-shaped flares are confined; accordingly, hosting active regions of J-shaped flares are more likely to be sigmoidal than non-J-shaped flares. Thus, J-shaped flares constitute a distinct subset of two-ribbon flares, probably representative of eruptive ones. Further, we found that combining the SRA and its associated magnetic flux has the potential to differentiate eruptive from confined flares.

We present XMM–Newton observations of N132D, the X-ray brightest supernova remnant in the Large Magellanic Cloud, using the Reflection Grating Spectrometer (RGS), which enables high-resolution spectroscopy in the soft X-ray band. A dozen emission lines from L-shell transitions of Si, S, Ar, Ca, and Fe at intermediate charge states are newly detected in the RGS data integrating the ∼200 ks on-axis observations. This enables accurate abundance measurements of these elements, whose K-shell emission is out of the RGS bandpass. The 0.3–2.0-keV spectra require at least three components of thermal plasmas with different electron temperatures and indicate clear evidence of non-equilibrium ionization (NEI). Our detailed spectral diagnostics further reveal that the forbidden-to-resonance line ratios of O vii and Ne ix are both higher than expected for typical NEI plasmas. This enhancement could be attributed to either resonance scattering or emission induced by charge exchange in addition to a possible contribution from the superposition of multiple-temperature components, although the lack of spatial information prevents us from concluding which is most likely.

Using the Atacama Large Millimeter/submillimeter Array, we have imaged 15 molecular-line emissions and the dust continuum emission around the Class 0 protostellar source IRAS 15398−3359. The outflow structure is mainly traced by the H₂CO (K_a = 0 and 1), CCH, and CS emissions. These lines also trace the disk/envelope structure around the protostar. The H₂CO (K_a = 2 and 3), CH₃OH, and SO emissions are concentrated toward the protostar, while the DCN emission is more extended around the protostar. We have performed principal component analysis (PCA) for these distributions on two different scales, the outflow and the disk/envelope structure. For the latter case, the molecular-line distributions are classified into two groups, according to the contribution of the second principal component, one having a compact distribution around the protostar and the other showing a rather extended distribution over the envelope. Moreover, the second principal component value tends to increase as an increasing quantum number of H₂CO (K_a = 0, 1, 2, and 3), reflecting the excitation condition: the distribution is more compact for higher excitation lines. These results indicate that PCA is effective at extracting the characteristic features of the molecular-line distributions around the protostar in an unbiased way. In addition, we identify four blobs in the outflow structure in the H₂CO lines, some of which can also be seen in the CH₃OH, CS, CCH, and SO emissions. The gas temperature derived from the H₂CO lines ranges from 43–63 K, which suggests shocks due to the local impact of the outflow on clumps of the ambient gas.

In 2015 October, the Be/X-ray binary 4U 0115+63 underwent a type II outburst, reaching an X-ray luminosity of ∼10³⁸ erg s⁻¹. During the outburst, Nuclear Spectroscopic Telescope Array (NuSTAR) performed two Target of Opportunity observations. Using the broadband spectra from NuSTAR (3–79 keV), we have detected multiple cyclotron lines of the source, i.e., ∼12, 16, 22, and 33/35 keV. Obviously, the 16 keV line is not a harmonic component of the 12 keV line. As described by the phase-dependent equivalent widths of these cyclotron lines, the 16 keV and 12 keV lines are two different fundamental lines. In our work, we apply the two-poles cyclotron line model to the observation, i.e., the two line sets are formed at the same altitude (∼0.2 km over the NS surface) of different magnetic poles, with ∼1.1 × 10¹² and 1.4 × 10¹² G in two poles, respectively.

The mass, origin, and evolutionary stage of the binary system LB-1 have been intensely debated, following the claim that it hosts an ∼70M_⊙ black hole, in stark contrast with the expectations for Galactic remnants. We conducted a high-resolution, phase-resolved spectroscopic study of its Paschen lines, using the Calar Alto 3.5 m telescope. We find that Paβ and Paγ (after subtraction of the stellar absorption component) are well fitted with a standard double-peaked disk profile. We measured the velocity shifts of the red and blue peaks at 28 orbital phases: the line center has an orbital motion in perfect antiphase with the secondary, and the radial velocity amplitude ranges from 8 to 13 km s⁻¹, for different methods of profile modeling. We interpret this curve as proof that the disk traces the orbital motion of the primary, ruling out the circumbinary disk and the hierarchical triple scenarios. The phase-averaged peak-to-peak half-separation (a proxy for the projected rotational velocity of the outer part of the disk) is ∼70 km s⁻¹, larger than the orbital velocity of the secondary and inconsistent with a circumbinary disk. From those results, we infer a primary mass 4–8 times higher than the secondary mass. Moreover, we show that the intensity ratio of the blue and red peaks has a sinusoidal behavior in phase with the secondary, which we attribute to external irradiation of the outer part of the disk. Finally, we discuss our findings in the context of competing scenarios proposed for LB-1. Further astrometric Gaia data will test between alternative solutions.

Numerical studies of gas accretion onto supermassive black hole binaries have generally been limited to conditions where the circumbinary disk (CBD) is 10–100 times thicker than expected for disks in active galactic nuclei. This discrepancy arises from technical limitations, and also from publication bias toward replicating fiducial numerical models. Here we present the first systematic study of how the binary's orbital evolution varies with disk scale height. We report three key results: (1) binary orbital evolution switches from outspiraling for warm disks (aspect ratio h/r ∼ 0.1), to inspiraling for more realistic cooler, thinner disks at a critical value of h/r ∼ 0.04, corresponding to orbital Mach number ${{ \mathcal M }}_{\mathrm{crit}}\approx 25$. (2) The net torque on the binary arises from a competition between positive torque from gas orbiting close to the black holes, and negative torque from the inner edge of the CBD, which is denser for thinner disks. This leads to increasingly negative net torques on the binary for increasingly thin disks. (3) The accretion rate is modestly suppressed with increasing Mach number. We discuss how our results may influence modeling of the nano-Hz gravitational-wave background, as well as estimates of the Laser Interferometer Space Antenna merger event rate.

During their formation, emerging protoplanets tidally interact with their natal disks. Proto–gas giant planets, with Hill radii larger than the disk thickness, open gaps and quench gas flow in the vicinity of their orbits. It is usually assumed that their type II migration is coupled to the viscous evolution of the disk. Although this hypothesis provides an explanation for the origin of close-in planets, it also encounters a predicament on the retention of long-period orbits for most gas giant planets. Moreover, numerical simulations indicate that the planets' migrations are not solely determined by the viscous diffusion of their natal disk. Here we carry out a series of hydrodynamic simulations combined with analytic studies to examine the transition between different paradigms of type II migration. We find a range of planetary mass for which gas continues to flow through a severely depleted gap so that the surface density distribution in the disk region beyond the gap is maintained in a quasi-steady state. The associated gap profile modifies the location of corotation and Lindblad resonances. In the proximity of the planet's orbit, high-order Lindblad and corotation torque are weakened by the gas depletion in the gap, while low-order Lindblad torques near the gap walls preserve their magnitude. Consequently, the intrinsic surface density distribution of the disk delicately determines both the pace and direction of the planets' type II migration. We show that this effect might stall the inward migration of giant planets and preserve them in disk regions where the surface density is steep.

We have carried out a search for substructure within the globular cluster (GC) systems of M84 (NGC 4374) and M86 (NGC 4406), two giant elliptical galaxies in the Virgo Cluster. We use wide-field (36' × 36'), multicolor broadband imaging to identify GC candidates in these two galaxies, as well as several other nearby lower-mass galaxies. Our analysis of the spatial locations of the GC candidates reveals several substructures, including a peak in the projected number density of GCs in M86 that is offset from the system center and may be at least partly due to the presence of the dwarf elliptical galaxy NGC 4406B, a bridge that connects the M84 and M86 GC systems, and a boxy isodensity contour along the southeast side of the M86 GC system. We divide our sample into red (metal-rich) and blue (metal-poor) GC candidates to look for differences in the spatial distributions of the two populations and find that the blue cluster candidates are the dominant population in each of the substructures we identify. We also incorporate the measurements from two radial velocity surveys of the GCs in the region and find that the bridge substructure is populated by GCs with a mix of velocities that are consistent with either M86 and M84, possibly providing further evidence for interaction signatures between the two galaxies.

We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.33 M_⊙) and low kinetic energy (≈1.3 × 10⁵⁰ erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of ∼0.1 M_⊙ located ∼1.2 × 10¹³ cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from ≳5 × 10¹³ cm to ≳2 × 10¹⁶ cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400–8200$\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ (i.e., 2%–12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.

We present detailed studies of the partially obscured quasar 2MASS J151653.23+190048.2 with continuous broadband spectrophotometry from near-infrared (NIR) through optical to ultraviolet (UV). The NIR and optical spectra show strong broad emission lines, while the UV spectrum is dominated by a set of rich intermediate-width emission lines (IELs). These IELs, unshifted with respect to the quasar systemic velocity measured by narrow emission lines, share a common profile of about 1900 $\mathrm{km}\,{{\rm{s}}}^{-1}$ in FWHM, in contrast to the Balmer and Paschen broad emission lines of FWHM ∼6300 $\mathrm{km}\,{{\rm{s}}}^{-1}$ observed in the optical and NIR. The intermediate width of these lines indicates that the emitting gas may come from the dusty torus region. However, the observed peculiar IEL intensity ratios, such as N vλ1240/Lyα, indicate that the emitting gas has a very high density, up to $\sim {10}^{13}\,{\mathrm{cm}}^{-3}$. Such a high density is unusual for gas around the dusty torus region, except that we consider mechanisms such as shocks that can produce local ultradense gas. We speculate that these emission lines could originate from the shock region, possibly induced by the quasar outflow colliding with the inner wall of the dusty torus. If true, this may give us an opportunity to peep at the quasar outflows at the scale of the dusty torus that have so far been elusive due to the limited resolving powers of existing facilities.

Photometric variability of a directly imaged exo-Earth conveys spatial information on its surface and can be used to retrieve a two-dimensional geography and axial tilt of the planet (spin–orbit tomography). In this study, we relax the assumption of the static geography and present a computationally tractable framework for dynamic spin–orbit tomography applicable to time-varying geography. First, a Bayesian framework of static spin–orbit tomography is revisited using analytic expressions of the Bayesian inverse problem with a Gaussian prior. We then extend this analytic framework to a time-varying one through a Gaussian process in the time domain, and present analytic expressions that enable efficient sampling from a full joint posterior distribution of geography, axial tilt, spin rotation period, and hyperparameters in the Gaussian process priors. Consequently, it only takes 0.3 s for a laptop computer to sample one posterior dynamic map conditioned on the other parameters with 3072 pixels and 1024 time grids, for a total of ∼3 × 10⁶ parameters. We applied our dynamic mapping method to a toy model and found that the time-varying geography was accurately retrieved along with the axial tilt and spin rotation period. In addition, we demonstrated the use of dynamic spin–orbit tomography with a real multicolor light curve of the Earth as observed by the Deep Space Climate Observatory. We found that the resultant snapshots from the dominant component of a principal component analysis roughly captured the large-scale, seasonal variations of the clear-sky and cloudy areas on the Earth.

We derive an equation of state (EOS) for magnetized charge-neutral nuclear matter relevant for a neutron star (NS). The calculations are performed within an effective chiral model based on the generalization of the σ model with nonlinear self-interactions of the σ mesons along with the ρ−σ cross-coupling term. This model is extended by introducing the contributions of a strong magnetic field on the charged particles. The contributions arising from the effects of the magnetic field on the Dirac sea of charged baryons are also included. The resulting EOS for the magnetized dense matter is used to investigate the NS properties like its mass, radius, and tidal deformability. The magnitude of the magnetic field at the core of the NS considered here is in the range of 10¹⁵–10¹⁸ G, for which the relative deformation from spherical symmetry turns out to be less than 1%, giving a post facto justification for the spherically symmetric treatment of the NS structure. The dimensionless tidal deformability Λ_1.4 is 526 for an NS with mass 1.4 M_⊙, which is consistent with the recent observation of GW 170817. The maximum mass of the NS in the presence of a strong magnetic field is consistent with the observational constraints on the mass of the pulsar PSR J0348–0432, and its radius at a mass of 1.4 M_⊙ is also in agreement with the empirical bounds.

We use MMT spectroscopy and deep Subaru Hyper Suprime-Cam (HSC) imaging to compare the spectroscopic central stellar velocity dispersion of quiescent galaxies with the effective dispersion of the dark matter halo derived from the stacked lensing signal. The spectroscopic survey (the Smithsonian Hectospec Lensing Survey) provides a sample of 4585 quiescent galaxy lenses with measured line-of-sight central stellar velocity dispersion (σ_SHELS) that is more than 85% complete for R < 20.6, D_n4000 > 1.5 and M_⋆ > 10^9.5M_⊙. The median redshift of the sample of lenses is 0.32. We measure the stacked lensing signal from the HSC deep imaging. The central stellar velocity dispersion is directly proportional to the velocity dispersion derived from the lensing σ_Lens, ${\sigma }_{\mathrm{Lens}}\,=(1.05\pm 0.15){\sigma }_{\mathrm{SHELS}}+(-21.17\pm 35.19)$. The independent spectroscopic and weak lensing velocity dispersions probe different scales, ∼3 kpc and ≳100 kpc, respectively, and strongly indicate that the observable central stellar velocity dispersion for quiescent galaxies is a good proxy for the velocity dispersion of the dark matter halo. We thus demonstrate the power of combining high-quality imaging and spectroscopy to shed light on the connection between galaxies and their dark matter halos.

We present the stellar population and ionized-gas outflow properties of ultraluminous IR galaxies (ULIRGs) at z = 0.1–1.0 that are selected from the AKARI far-IR all-sky survey. We construct a catalog of 1077 ULIRGs to examine feedback effects after major mergers. Of the 1077 ULIRGs, 202 are spectroscopically identified by SDSS and Subaru/FOCAS observations. Thanks to the deeper depth and higher resolution of AKARI compared to the previous Infrared Astronomical Satellite (IRAS) survey and reliable identification from the Wide-field Infrared Survey Explorer (WISE) mid-IR pointing, the sample is unique in identifying optically faint (i ∼ 20) IR-bright galaxies, which could be missed in previous surveys. A self-consistent spectrum and broadband spectral energy distribution (SED) decomposition method, which constrains stellar population properties in SED modeling based on spectral fitting results, has been employed for 149 ULIRGs whose optical continua are dominated by host galaxies. They are massive galaxies (${M}_{\mathrm{star}}\sim {10}^{11}$–10¹²M${}_{\odot }$) associated with intense star formation activities (SFR ∼ 200–2000 M${}_{\odot }$ yr⁻¹). The sample covers a range of active galactic nucleus (AGN) bolometric luminosity of 10¹⁰–10¹³L${}_{\odot }$, and the outflow velocity measured from the [O iii] 5007 Å line shows a correlation with AGN luminosity. Eight galaxies show extremely fast outflows with velocity up to 1500–2000 km s⁻¹. However, the coexistence of vigorous starbursts and strong outflows suggests the star formation has not been quenched during the ULIRG phase. By deriving the stellar mass and mass fraction of the young stellar population, we find no significant discrepancies between stellar properties of ULIRGs with weak and powerful AGNs. The results are not consistent with the merger-induced evolutionary scenario, which predicts that star formation–dominated ULIRGs will show smaller stellar masses and younger stellar populations compared to AGN-dominated ULIRGs.

Magnetic reconnection is a fundamental and important physical process that can release magnetic energy and change magnetic topology. A statistic study of reconnected magnetic field lines has been carried out by Cluster spacecraft 1 during 58 current sheet crossing events. We calculated the values of $| {B}_{n}/B|$ at different distances from reconnection site to describe the loosing process of magnetic field lines. Our results suggest that current sheets in ion diffusion regions have small values of $| {B}_{n}/B|$. As the distance from reconnection site increases, the reconnected magnetic field lines relax, and subsequently have relatively large values of $| {B}_{n}/B|$. However, such large values of $| {B}_{n}/B|$ are found to be closely related to open magnetic field lines that connect the Earth's magnetosphere and the solar wind.

We select 13 nearby spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) project and perform spectral energy distribution fitting for each galaxy applying two-component modified blackbody models on a global scale aim to probe the potential submillimeter (submm) excess. We find that NGC 2976, NGC 3351, and NGC 4631 show excess emission at 850 μm when using β_c = 2.0. The contributions of CO(3–2), free–free emission or synchrotron radiation cannot explain their 850 μm excess. Our results suggest that a submm excess at 850 μm may be more easily detected for galaxies with faint total infrared luminosity and low cold dust mass. The colder temperature of cold dust, the more radiation of dust there is at 850 μm. The submm excess are prone to be detected in spiral galaxies with low stellar mass. As the metallicity of galaxies become poor, the submm excess is more obvious.

The recently observed diversity of Type Ia supernovae (SNe Ia) has motivated us to conduct the theoretical modeling of SNe Ia for a wide parameter range. In particular, the origin of Type Iax supernovae (SNe Iax) has been obscure. Following our earlier work on the parameter dependence of SN Ia models, we focus on SNe Iax in the present study. For a model of SNe Iax, we adopt the currently leading model of pure turbulent deflagration of near-Chandrasekhar mass C+O white dwarfs (WDs). We carry out two-dimensional hydrodynamical simulations of the propagation of the deflagration wave, which leaves a small WD remnant behind and ejects nucleosynthesis materials. We show how the explosion properties, such as nucleosynthesis and explosion energy, depend on the model parameters, such as central densities and compositions of the WDs (including the hybrid WDs), turbulent flame prescription, and initial flame geometry. We extract the associated observables in our models and compare with the recently discovered low-mass WDs with unusual surface abundance patterns and the abundance patterns of some SN remnants. We provide the nucleosynthesis yield tables for applications to stellar archeology and galactic chemical evolution. Our results are compared with the representative models in the literature.

We present a catalog of emissive point sources detected in the SPT-SZ survey, a contiguous 2530 square degree area surveyed with the South Pole Telescope (SPT) from 2008–2011 in three bands centered at 95, 150, and 220 GHz. The catalog contains 4845 sources measured at a significance of 4.5σ or greater in at least one band, corresponding to detections above approximately 9.8, 5.8, and 20.4 mJy in 95, 150, and 220 GHz, respectively. The spectral behavior in the SPT bands is used for source classification into two populations based on the underlying physical mechanisms of compact, emissive sources that are bright at millimeter wavelengths: synchrotron radiation from active galactic nuclei and thermal emission from dust. The latter population includes a component of high-redshift sources often referred to as submillimeter galaxies (SMGs). In the relatively bright flux ranges probed by the survey, these sources are expected to be magnified by strong gravitational lensing. The survey also contains sources consistent with protoclusters, groups of dusty galaxies at high redshift undergoing collapse. We cross-match the SPT-SZ catalog with external catalogs at radio, infrared, and X-ray wavelengths and identify available redshift information. The catalog splits into 3980 synchrotron-dominated and 865 dust-dominated sources, and we determine a list of 506 SMGs. Ten sources in the catalog are identified as stars. We calculate number counts for the full catalog, and synchrotron and dusty components, using a bootstrap method and compare our measured counts with models. This paper represents the third and final catalog of point sources in the SPT-SZ survey.

Using 8.4 yr of photometry from the AllWISE/NEOWISE multi-epoch catalogs, we compare the mid-infrared variability properties of a sample of 2197 dwarf galaxies (M_⋆ < 2 × 10⁹h⁻²M_☉) to a sample of 6591 more massive galaxies (M_⋆ ≥ 10¹⁰h⁻²M_☉) matched in mid-infrared apparent magnitude. We find only two dwarf galaxies with mid-infrared variability, a factor of ∼10 less frequent than the more massive galaxies (p = 6 × 10⁻⁶), consistent with previous findings of optical variability in low-mass and dwarf galaxies using data with a similar baseline and cadence. Within the more massive control galaxy population, we see no evidence for a stellar mass dependence of mid-infrared variability, suggesting that this apparent reduction in the frequency of variable objects occurs below a stellar mass of ∼10¹⁰h⁻²M_☉. Compared to the more massive galaxies, active galactic nuclei (AGNs) selected in dwarf galaxies using either their mid-infrared color or optical emission-line classification are systematically missed by variability selection. Our results suggest, in agreement with previous optical studies at similar cadence, that variability selection of AGNs in dwarf galaxies is ineffective unless higher-cadence data are used.

We show that point sources of dark energy can explain accelerated late-time expansion and, simultaneously, satisfy observational constraints on massive compact objects. Population III stellar collapse into GEneric Objects of Dark Energy (GEODEs) between 8 ≲ z ≲ 20 mimics the observed Ω_Λ within the typical concordance cosmology. We determine the appropriate dynamical model of aggregate GEODE flow within covariant linear perturbation theory. We find that all continuum fluid properties, at large scales, are determined by the internal properties and spin of individual GEODEs. For large spin, the spatial distribution of GEODEs becomes uniform on scales ≲200 Mpc. The power spectrum of cold dark matter is essentially unaltered. A Population III GEODE scenario provides an observationally consistent physical origin for accelerated late-time expansion while imposing no new constraints on structure formation.

The size of the dust torus in active galactic nuclei (AGNs) and their high-luminosity counterparts, quasars, can be inferred from the time delay between UV/optical accretion disk continuum variability and the response in the mid-infrared (MIR) torus emission. This dust reverberation mapping (RM) technique has been successfully applied to ∼70 z ≲ 0.3 AGNs and quasars. Here we present first results of our dust RM program for distant quasars covered in the Sloan Digital Sky Survey Stripe 82 region combining ∼20 yr ground-based optical light curves with 10 yr MIR light curves from the WISE satellite. We measure a high-fidelity lag between W1 band (3.4 μm) and g band for 587 quasars over 0.3 ≲ z ≲ 2 ($\left\langle z\right\rangle \sim 0.8$) and two orders of magnitude in quasar luminosity. They tightly follow (intrinsic scatter ∼0.17 dex in lag) the IR lag–luminosity relation observed for z < 0.3 AGNs, revealing a remarkable size–luminosity relation for the dust torus over more than four decades in AGN luminosity, with little dependence on additional quasar properties such as Eddington ratio and variability amplitude. This study motivates further investigations in the utility of dust RM for cosmology and strongly endorses a compelling science case for the combined 10 yr Vera C. Rubin Observatory Legacy Survey of Space and Time (optical) and 5 yr Nancy Grace Roman Space Telescope 2 μm light curves in a deep survey for low-redshift AGN dust RM with much lower luminosities and shorter, measurable IR lags. The compiled optical and MIR light curves for 7384 quasars in our parent sample are made public with this work.

Astrophysical jets are launched from strongly magnetized systems that host an accretion disk surrounding a central object. The origin of the jet-launching magnetic field is one of the open questions for modeling the accretion–ejection process. Here we address the question of how the accretion-disk magnetization and field structure required for jet launching are generated. Applying the PLUTO code, we present the first resistive magnetohydronamic simulations of jet launching including a nonscalar accretion-disk mean-field α²Ω dynamo in the context of large-scale disk-jet simulations. Essentially, we find the α_ϕ-dynamo component determining the amplification of the poloidal magnetic field, which is strictly related to the disk magnetization (and, as a consequence, to the jet speed, mass, and collimation), while the α_R- and α_θ-dynamo components trigger the formation of multiple, antialigned magnetic loops in the disk, with strong consequences for the stability and dynamics of the disk–jet system. In particular, such loops trigger the formation of dynamo-inefficient zones, which are characterized by a weak magnetic field and therefore a lower value of the magnetic diffusivity. The jet mass, speed, and collimation are strongly affected by the formation of the dynamo-inefficient zones. Moreover, the θ component of the α dynamo plays a key role when the dynamo interacts with a nonradial component of the seed magnetic field. We also present correlations between the strength of the disk toy dynamo coefficients and the dynamical parameters of the jet that is launched.

Astrophysical jets are launched from strongly magnetized systems that host an accretion disk surrounding a central object. Here we address the question of how accretion-disk magnetization and the field structure required for jet launching are generated. We continue our work from Mattia & Fendt (Paper I) by considering a nonscalar accretion-disk mean-field α²Ω dynamo in the context of large-scale disk-jet simulations. We now investigate a disk dynamo that follows analytical solutions of the mean-field dynamo theory, essentially based only on a single parameter, the Coriolis number. We thereby confirm the anisotropy of the dynamo tensor acting in accretion disks, allowing both the resistivity and mean-field dynamo to be related to the disk turbulence. Our new model recovers previous simulations by applying a purely radial initial field while allowing for a more stable evolution for seed fields with a vertical component. We also present correlations between the strength of the disk dynamo coefficients and the dynamical parameters of the jet that is launched, and discuss their implications for observed jet quantities.

Large-scale outflows in star-forming galaxies are observed to be ubiquitous and are a key aspect of theoretical modeling of galactic evolution, the focus of the Simulating Multiscale Astrophysics to Understand Galaxies (SMAUG) project. Gas blown out from galactic disks, similar to gas within galaxies, consists of multiple phases with large contrasts of density, temperature, and other properties. To study multiphase outflows as emergent phenomena, we run a suite of rougly parsec-resolution local galactic disk simulations using the TIGRESS framework. Explicit modeling of the interstellar medium (ISM), including star formation and self-consistent radiative heating plus supernova feedback, regulates ISM properties and drives the outflow. We investigate the scaling of outflow mass, momentum, energy, and metal loading factors with galactic disk properties, including star formation rate (SFR) surface density (Σ_SFR ∼ 10⁻⁴ − 1 M_⊙ kpc⁻² yr⁻¹), gas surface density (${{\rm{\Sigma }}}_{\mathrm{gas}}\sim 1\mbox{--}100\,{M}_{\odot }\,{\mathrm{pc}}^{-2}$), and total midplane pressure (or weight; ${P}_{\mathrm{mid}}\approx { \mathcal W }\sim {10}^{3}\mbox{--}{10}^{6}\,{k}_{B}\,{\mathrm{cm}}^{-3}\,{\rm{K}}$). The main components of outflowing gas are mass-delivering cool gas (T ∼ 10⁴ K) and energy/metal-delivering hot gas (T ≳ 10⁶ K). Cool mass outflow rates measured at outflow launch points (one or two scale heights $\sim 300\,\mathrm{pc}\mbox{--}1\,\mathrm{kpc}$) are 1–100 times the SFR (decreasing with Σ_SFR), although in massive galaxies most mass falls back owing to insufficient outflow velocity. The hot galactic outflow carries mass comparable to 10% of the SFR, together with 10%–20% of the energy and 30%–60% of the metal mass injected by SN feedback. Importantly, our analysis demonstrates that in any physically motivated cosmological wind model it is crucial to include at least two distinct thermal wind components.

Observations of bright protoplanetary disks often show annular gaps in their dust emission. One interpretation of these gaps is disk–planet interaction. If so, fitting models of planetary gaps to observed protoplanetary disk gaps can reveal the presence of hidden planets. However, future surveys are expected to produce an ever-increasing number of protoplanetary disks with gaps. In this case, performing a customized fitting for each target becomes impractical owing to the complexity of disk–planet interaction. To this end, we introduce Disk Planet Neural Network (DPNNet), an efficient model of planetary gaps by exploiting the power of machine learning. We train a deep neural network with a large number of dusty disk–planet hydrodynamic simulations across a range of planet masses, disk temperatures, disk viscosities, disk surface density profiles, particle Stokes numbers, and dust abundances. The network can then be deployed to extract the planet mass for a given gap morphology. In this work, first in a series, we focus on the basic concepts of our machine learning framework. We demonstrate its utility by applying it to the dust gaps observed in the protoplanetary disk around HL Tau at 10, 30, and 80 au. Our network predicts planet masses of 80 M_⊕, 63 M_⊕, and 70 M_⊕, respectively, which are comparable to those from other studies based on specialized simulations. We discuss the key advantages of our DPNNet in its flexibility to incorporate new physics as well as any number of parameters and predictions, in addition to its potential to ultimately replace hydrodynamical simulations for disk observers and modelers.

Previous studies suggested that the interplanetary magnetic field (IMF) has a significant influence on the Venusian-induced magnetosphere. We present observations by Venus Express under a nearly flow-aligned IMF condition to investigate the demagnetization of the Venusian ionosphere. Our results show that the magnetic barrier becomes weak and narrow, and the ionosphere can be demagnetized under the IMF with the dominating flow-aligned component while the solar wind dynamic pressure remains almost unchanged. The demagnetization of the Venusian ionosphere implies that the total pressure of the magnetic barrier above the ionopause decreases. The magnetic field lines upstream from Venus drape differently under the nearly flow-aligned IMF condition. And thus the upstream solar wind flow is affected by the outward magnetic tension, which leads to the decrease of the dynamic pressure that directly acts on the magnetic barrier.

Active galaxies form a clear pattern in the optical plane showing the correlation between the FWHM of the Hβ line and the ratio of the equivalent width (EW) of the optical Fe ii emission and the broad EW(Hβ). This pattern is frequently referred to as the quasar main sequence. In this paper, we study the UV plane showing the FWHM of Mg ii line against the ratio of the EW of UV Fe ii emission to the broad EW(Mg ii). We show that the UV plane trends are different, with the underlying strong correlation between the FWHM(Mg ii) and the EW(Mg ii). This correlation is entirely driven by the choice of the continuum used to measure the EW(Mg ii). If instead of the observationally determined continuum, we use a theoretically motivated power law extrapolated from the wide wavelength range, the behavior of the FWHM versus EW for Mg ii becomes similar to the behavior for Hβ. Such a similarity is expected since both the lines belong to the low-ionization group of emission lines and come from a similar region. We discuss the behavior of the lines in the context of the broad line region model based on the presence of dust in the accretion disk atmosphere.

The ability to predict the occurrence of solar flares in advance is important to humankind due to the potential damage they can cause to Earth's environment and infrastructure. It has been shown in Kusano et al. that a small-scale bipolar region (BR), with its flux reversed relative to the potential component of the overlying field, appearing near the polarity inversion line (PIL) is sufficient to effectively trigger a solar flare. In this study we perform further 3D magnetohydrodynamic simulations to study the effect that the motion of these small-scale BRs has on the effectiveness of flare triggering. The effect of two small-scale BRs colliding is also simulated. The results indicate that the strength of the triggered flare is dependent on how much of the overlying field is disrupted by the BR. Simulations of linear oscillations of the BR showed that oscillations along the PIL increase the flare strength while oscillations across the PIL detract from the flare strength. The flare strength is affected more by larger amplitude oscillations but is relatively insensitive to the frequency of oscillations. In the most extreme case the peak kinetic energy of the flare increased more than threefold compared to a non-oscillating BR. Simulations of torsional oscillations of the BR showed a very small effect on the flare strength. Finally, simulations of colliding BRs showed the generation of much stronger flares as the flares triggered by each individual BR coalesce. These results show that significantly stronger flares can result from motion of the BR along the PIL of a sheared field or from the presence of multiple BRs in the same region.

Recently, magnetic reconnection, where a relativistically hot plasma is confined by a strong magnetic field, has received great attention in relation to astrophysical objects (e.g., a pulsar magnetosphere and magnetar). However, reconnection with a relativistic high-speed drift current in the plasma sheet has not been investigated yet. Thus, from both theoretical and computational points of view, we studied the growth rate of relativistic reconnection for the high-speed drift current in a relativistically hot plasma sheet. Consequently, we argue that, contrary to the conventional understanding of the fast energy dissipation by the relativistic reconnection, the growth of magnetic reconnection is suppressed.

Gamma-ray bursts (GRBs) are considered one of the most violent, explosive events in the universe and serve as high-redshift probes for cosmological study due to their high-energy observations. Such observations, particularly in the GeV regime, have already proven fruitful for deriving useful scientific results, such as the determination of extragalactic background light (EBL) and the stringent constraint on the Lorentz invariance violation effect. Owing to the advantages of a very large effective area, a low threshold energy, a wide field of view, and high duty cycle, the upcoming Large High Altitude Air Shower Observatory–Water Cerenkov Detector Array (LHAASO-WCDA) will have potential sensitivity for discovering GRBs in the 100 GeV energy region. In this work, a sample of GRBs has been generated and examined based on existing observations reported by the Large Area Telescope on board the Fermi satellite. The Fermi spectra are extrapolated to high energy by taking into account the absorption due to the pair production processes occurring between γ rays and EBL. With an assumption that an ultrahigh-energy component accounts for 10% of the total luminosity, it is found that LHAASO-WCDA has a GRB detection rate of ∼one GRB per year.

This paper presents a new approach to deriving far-infrared (FIR) photometric redshifts for galaxies based on their reprocessed emission from dust at rest-frame FIR through millimeter wavelengths. FIR photometric redshifts ("FIR-z") have been used over the past decade to derive redshift constraints for highly obscured galaxies that lack photometry at other wavelengths like the optical/near-IR. Most literature FIR-z fits are performed through ${\chi }^{2}$ minimization to a single galaxy's FIR template spectral energy distribution (SED). The use of a single galaxy template, or modest set of templates, can lead to an artificially low uncertainty estimate on FIR-z's because real galaxies display a wide range in intrinsic dust SEDs. I use the observed distribution of galaxy SEDs (for well-constrained samples across $0\lt z\lt 5$) to motivate a new FIR through millimeter photometric redshift technique called MMpz. The MMpz algorithm asserts that galaxies are most likely drawn from the empirically observed relationship between rest-frame peak wavelength, ${\lambda }_{\mathrm{peak}}$, and total IR luminosity, L${}_{\mathrm{IR}}$; the derived photometric redshift accounts for the measurement uncertainties and intrinsic variation in SEDs at the inferred L${}_{\mathrm{IR}}$, as well as heating from the cosmic microwave background at $z\gtrsim 5$. The MMpz algorithm has a precision of ${\sigma }_{{\rm{\Delta }}z/(1+z)}\approx 0.3\mbox{--}0.4$, similar to single-template fits, while providing a more accurate estimate of the FIR-z uncertainty with reduced chi-squared of order ${ \mathcal O }({\chi }_{\nu }^{2})=1$, compared to alternative FIR photometric redshift techniques (with ${ \mathcal O }({\chi }_{\nu }^{2})\approx 10\mbox{--}{10}^{3}$).

The leading tensions to the collisionless cold dark matter (CDM) paradigm are the "small-scale controversies," discrepancies between observations at the dwarf-galactic scale, and their simulational counterparts. In this work we consider methods to infer 3D morphological information on Local Group dwarf spheroidals and test the fitness of CDM+hydrodynamics simulations to the observed galaxy shapes. We find that the subpopulation of dwarf galaxies with mass-to-light ratio $\gtrsim 100{M}_{\odot }/{L}_{\odot }$ reflects an oblate morphology. This is discrepant with the dwarf galaxies with mass-to-light ratios $\lesssim 100{M}_{\odot }/{L}_{\odot }$, which reflect prolate morphologies, as well as simulations of CDM-sourced bright isolated galaxies that are explicitly prolate. Although more simulations and data are called for if evidence of oblate pressure-supported stellar distributions persists in observed galaxies while being absent from simulations, we argue that an underlying oblate non-CDM dark matter halo may be required and present this as motivation for future studies.

In the context of a cosmography approach to using the data of the Hubble diagram for supernovae, quasars, and gamma-ray bursts, we study dark energy (DE) parameterizations and the concordance cold dark matter (ΛCDM) universe. Using different combinations of data samples including (i) supernovae (Pantheon), (ii) Pantheon + quasars. and (iii) Pantheon + quasars + gamma-ray bursts, and applying the minimization of χ² function of the distance modulus of data samples in the context of the Markov Chain Monte Carlo method, we obtain constrained values of cosmographic parameters in a model-independent cosmography scenario. We then investigate our analysis, for different concordance ΛCDM cosmology, wCDM, Chevallier–Polarski–Linder, and Pade parameterizations. Comparing the numerical values of the cosmographic parameters obtained for DE scenarios with those of the model-independent method, we show that the concordance ΛCDM model has serious issues when we involve quasar and gamma-ray burst data in our analysis. While high-redshift quasars and gamma-ray bursts can falsify the concordance model, our results using a cosmography approach indicate that the other DE parameterizations are still consistent with these observations.

We report on recent upgrades to our general relativistic radiation-magnetohydrodynamics code, Cosmos++, which expands the two-moment, M₁, radiation treatment from gray to multi-frequency transport, including Doppler and gravitational frequency shifts. The solver accommodates either photon (Bose–Einstein) or neutrino (Fermi–Dirac) statistical distribution functions with absorption, emission, and elastic scattering processes. An implicit scheme is implemented to simultaneously solve the primitive inversion problem together with the radiation–matter coupling source terms, providing stability over a broad range of opacities and optical depths where the interaction terms can be stiff. We discuss our formulations and numerical methods, and validate our methods against a wide variety of test problems spanning optically thin to thick regimes in flat, weakly curved, and strongly curved spacetimes.

High-redshift blazars are valuable tools to study the early universe. So far, only a handful of γ-ray blazars have been found at redshifts above 3. Gamma-ray signals are detected in the direction of PMN J2219–2719 (z = 3.63) and PMN J2321–0827 (z = 3.16) by analyzing the 10 yr Fermi-LAT Pass 8 data. PMN J2219–2719 is not distinguished from the background in the global analysis. During the 5 month epoch, the TS value is 47.8 and the flux is more than 10 times that of the 10 yr averaged flux. In addition, the angular distance between the γ-ray position and the radio position of PMN J2219–2719 is only 004. Moreover, the long timescale γ-ray and infrared light curves are very similar, which supports the association between the γ-ray source and PMN J2219–2719. The global analysis of PMN J2321–0827 suggest a new γ-ray source; during the flare phase, the TS value is 61.4 and the γ-ray flux increased significantly. The association probability suggests that PMN J2321–0827 may be the counterpart of the new γ-ray source. In the future, the number of high-redshift γ-ray sources will increase by combining Fermi-LAT and the upcoming Large Synoptic Survey Telescope.

We present a spectroscopic analysis of the recently discovered fast-evolving Type I superluminous supernova (SLSN-I) SN 2019neq (at redshift z = 0.1059). We compare it to the well-studied slowly evolving SLSN-I SN 2010kd (z = 0.101). Our main goal is to search for spectroscopic differences between the two groups of SLSNe-I. Differences in the spectra may reveal different ejecta compositions and explosion mechanisms. Our investigation concentrates on optical spectra observed with the 10 m Hobby–Eberly Telescope Low Resolution Spectrograph-2 at McDonald Observatory during the photospheric phase. We apply the SYN++ code to model the spectra of SN 2019neq taken at −4 days, +5 days, and +29 days from maximum light. We examine the chemical evolution and ejecta composition of the SLSN by identifying the elements and ionization states in its spectra. We find that a spectral model consisting of O iii, Co iii, and Si iv gives a SYN++ fit that is comparable to the typical SLSN-I spectral model consisting of O ii, and conclude that the true identification of those lines, at least in the case of SN 2019neq, is ambiguous. Based on modeling the entire optical spectrum, we classify SN 2019neq as a fast-evolving SLSN-I having a photospheric velocity gradient of $\dot{v}\sim 375$ km s⁻¹ day⁻¹, which is among the highest velocity gradients observed for an SLSN-I. Inferring the velocity gradient from the proposed Fe iiλ5169 feature alone would result in $\dot{v}\sim 100$ km s⁻¹ day⁻¹, which is still within the observed range of fast-evolving SLSNe-I. In addition, we derive the number density of relevant ionization states for a variety of identified elements at the epoch of the three observations. Finally, we give constraints on the lower limit of the ejecta mass and find that both SLSNe have an ejecta mass at least one order of magnitude higher than normal SNe Ia, while the fast-evolving SN 2019neq has an ejecta mass a factor of two lower than the slowly evolving SN 2010kd. These mass estimates suggest the existence of a possible correlation between the evolution timescale and the ejected mass of SLSNe-I.

The temporal and spatial variability of the radiation environment around Ganymede has a direct impact on the moon's exosphere, which links Jupiter's magnetosphere with the satellite's icy surface. The dynamics of the entry and circulation inside Ganymede's magnetosphere of the Jovian energetic ions, as well as the morphology of their precipitation on the moon's surface, determine the variability of the sputtered-water release. For this reason, the so-called planetary space weather conditions around Ganymede can also have a long-term impact on the weathering history of the moon's surface. In this work, we simulate the Jovian energetic ion precipitation to Ganymede's surface for different relative configurations between the moon's magnetic field and Jupiter's plasma sheet using a single-particle Monte Carlo model driven by the electromagnetic fields from a global MHD model. In particular, we study three science cases characterized by conditions similar to those encountered during the NASA Galileo G2, G8, and G28 flybys of Ganymede (i.e., when the moon was above, inside, and below the center of Jupiter's plasma sheet). We discuss the differences between the various surface precipitation patterns and the implications in the water sputtering rate. The results of this preliminary analysis are relevant to ESA's JUICE mission and in particular to the planning and optimization of future observation strategies for studying Ganymede's environment.

To improve the forecasting capability of impactful solar energetic particle (SEP) events, the relation between coronal mass ejections (CMEs) and SEP events needs to be better understood. Here we present a statistical study of SEP occurrences and timescales with respect to the CME source locations and speeds, considering all 257 fast (v_CME ≥ 900 km s⁻¹) and wide (angular width ≥60°) CMEs that occurred between 2006 December and 2017 October. We associate them with SEP events at energies above 10 MeV. Examination of the source region of each CME reveals that CMEs more often accompany a SEP event if they originate from the longitude of E20–W100 relative to the observer. However, an SEP event could still be absent if the CME is <2000 km s⁻¹. For the associated CME–SEP pairs, we compute three timescales for each of the SEP events, namely the timescale of the onset (TO), the rise time (TR), and the duration (TD). They are correlated with the longitude of the CME source region relative to the footpoint of the Parker spiral (ΔΦ) and v_CME. The TO tends to be short for $| {\rm{\Delta }}{\rm{\Phi }}| \ \lt$ 60°. This trend is weaker for TR and TD. The SEP timescales are only weakly correlated with v_CME. Positive correlations of both TR and TD with v_CME are seen in poorly connected (large $| {\rm{\Delta }}{\rm{\Phi }}|$) events. Additionally, TO appears to be negatively correlated with v_CME for events with small $| {\rm{\Delta }}{\rm{\Phi }}|$.

Aimed to be ready for the transition from research to operation, we have developed a solar wind model by coupling a data-driven empirical coronal model with a magnetohydrodynamics heliospheric model. We performed a data-driven simulation of the solar wind for a two-year period during the declining and minimum phases of solar cycle 23. Comparisons with OMNI and Ulysses spacecraft data show that the model can reproduce the large-scale variations of the solar wind plasma parameters. The evolution of geocentric solar magnetospheric (GSM) B_x and B_z components are also reasonably duplicated by the model in terms of polarity and strength. Apparent signatures of the Russell–McPherron (R-M) effect are found from both observed data and simulated results, indicating that during the investigated interval the R-M effect is the dominant mechanism that controls the large-scale evolution of the north–south component of the interplanetary magnetic field in the GSM frame. The results demonstrate that the established model can provide valuable space weather information about the solar wind.

A black hole embedded within a bright, optically thin emitting region imprints a nearly circular "shadow" on its image, corresponding to the observer's line of sight into the black hole. The shadow boundary depends on the black hole's mass and spin, providing an observable signature of both properties via high-resolution images. However, standard expressions for the shadow boundary are most naturally parametrized by Boyer–Lindquist radii rather than by image coordinates. We explore simple, approximate parameterizations for the shadow boundary using ellipses and a family of curves known as limaçons. We demonstrate that these curves provide excellent and efficient approximations for all black hole spins and inclinations. In particular, we show that the two parameters of the limaçon naturally account for the three primary shadow deformations resulting from mass and spin: size, displacement, and asymmetry. These curves are convenient for parametric model fitting directly to interferometric data, they reveal the degeneracies expected when estimating black hole properties from images with practical measurement limitations, and they provide a natural framework for parametric tests of the Kerr metric using black hole images.

The black hole candidate EXO 1846-031 underwent an outburst in 2019, after at least 25 yr in quiescence. We observed the system using NuSTAR on 2019 August 3. The 3–79 keV spectrum shows strong relativistic reflection features. Our baseline model gives a nearly maximal black hole spin value of $a={0.997}_{-0.002}^{+0.001}$ (1σ statistical errors). This high value nominally excludes the possibility of the central engine harboring a neutron star. Using several models, we test the robustness of our measurement to assumptions about the density of the accretion disk, the nature of the corona, the choice of disk continuum model, and the addition of reflection from the outer regions of the accretion disk. All tested models agree on a very high black hole spin value and a high value for the inclination of the inner accretion disk of $\theta \approx 73^\circ$. We discuss the implications of this spin measurement in the population of stellar mass black holes with known spins, including LIGO and Virgo events.

We present a Chandra archival study of optically selected active galactic nucleus (AGN) pairs at a median redshift $\bar{z}\sim 0.1$. Out of 1286 AGN pairs (with projected separations r_p < 100 kpc and velocity offsets Δv < 600 km s⁻¹) optically identified from the Sloan Digital Sky Survey Seventh Data Release, we find 67 systems with archival Chandra observations, which represents the largest sample of optically selected AGN pairs studied in the X-ray. Among the 67 AGN pairs, 21 systems have both nuclei detected in the X-ray, 36 have one nucleus detected in the X-ray, and 10 have no X-ray detection. The X-ray detection rate, 78/134 = 58% (±7% 1σ Poisson errors), is significantly higher than that (23/134 = 17% ± 4%) of a comparison sample of star-forming galaxy pairs, lending support to the optical AGN classification. In the conservative case where X-ray contamination from star formation is removed, the X-ray detection rate becomes 27% ± 4%, consistent with predictions from the latest galaxy merger simulations. The 2–10 keV X-ray luminosity L_{2–10 keV} increases with decreasing projected separation in AGN pairs for r_p ≳ 15 kpc, suggesting an enhancement of black hole accretion even in early-stage mergers. On the other hand, L_{2–10 keV} appears to decrease with decreasing projected separation at r_p ≲15 kpc, which is contradictory to predictions from merger simulations. The apparent decrease in L_{2–10 keV} of AGN pairs at r_p ≲ 15 kpc may be caused by (i) enhanced absorbing columns from merger-induced gas inflows, (ii) feedback effects from early-stage mergers, and/or (iii) small number statistics. Future X-ray studies with larger samples are needed to put our results on firmer statistical ground.

Gravitational wave (GW) measurements provide the most robust constraints of the mass of astrophysical black holes. Using state-of-the-art GW signal models and a unique parameter estimation technique, we infer the source parameters of the loudest marginal trigger, GW170502, found by LIGO from 2015 to 2017. If this trigger is assumed to be a binary black hole merger, we find it corresponds to a total mass in the source frame of ${157}_{-41}^{+55}\,{\text{}}{M}_{\odot }$ at redshift $z={1.37}_{-0.64}^{+0.93}$. The primary and secondary black hole masses are constrained to ${94}_{-28}^{+44}\,{\text{}}{M}_{\odot }$ and ${62}_{-25}^{+30}\,{\text{}}{M}_{\odot }$, respectively, with 90% confidence. Across all signal models, we find ≳70% probability for the effective spin parameter χ_eff > 0.1. Furthermore, we find that the inclusion of higher-order modes in the analysis narrows the confidence region for the primary black hole mass by 10%; however, the evidence for these modes in the data remains negligible. The techniques outlined in this study could lead to robust inference of the physical parameters for all intermediate-mass black hole binary candidates (≳100 M_⊙) in the current GW network.

The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub)millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized particles are trapped at the location of the continuum peak. In this paper, we present 860 μm ALMA observations of polarized dust emission from this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be 1%–2%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of ∼100 μm. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both ALMA polarization and previous ALMA and Very Large Array observations, we suggest that the thermal emission at 860 μm wavelength is optically thick (τ_abs ∼ 7.3) at the dust trap with a maximum observable grain size of ∼100 μm rather than an optically thin case with centimeter-sized dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 μm thermal emission is optically thick.

We address the problem of the origin of massive stars, namely the origin, path, and timescale of the mass flows that create them. Based on extensive numerical simulations, we propose a scenario where massive stars are assembled by large-scale, converging, inertial flows that naturally occur in supersonic turbulence. We refer to this scenario of massive-star formation as the inertial-inflow model. This model stems directly from the idea that the mass distribution of stars is primarily the result of turbulent fragmentation. Under this hypothesis, the statistical properties of turbulence determine the formation timescale and mass of prestellar cores, posing definite constraints on the formation mechanism of massive stars. We quantify such constraints by analyzing a simulation of supernova-driven turbulence in a 250 pc region of the interstellar medium, describing the formation of hundreds of massive stars over a time of approximately 30 Myr. Due to the large size of our statistical sample, we can say with full confidence that massive stars in general do not form from the collapse of massive cores nor from competitive accretion, as both models are incompatible with the numerical results. We also compute synthetic continuum observables in the Herschel and ALMA bands. We find that, depending on the distance of the observed regions, estimates of core mass based on commonly used methods may exceed the actual core masses by up to two orders of magnitude and that there is essentially no correlation between estimated and real core masses.

PS15dpn is a luminous rapidly rising Type Ibn supernova (SN) discovered by Pan-STARRS1. Previous study has showed that its bolometric light curve (LC) cannot be explained by the ⁵⁶Ni model. In this paper, we used the ⁵⁶Ni model, the magnetar model, the circumstellar interaction (CSI) model, and the CSI plus ⁵⁶Ni model to fit the bolometric LC of PS15dpn. We found that the ⁵⁶Ni model can fit the bolometric LC but the parameters are unrealistic, and that the magnetar model, the CSI model, and the CSI plus ⁵⁶Ni model can match the data with reasonable parameters. Considering the fact that the emission lines indicative of the interaction between the ejecta and the circumstellar medium (CSM) have been confirmed, and that the SNe produced by the explosions of massive stars can synthesize moderate amounts of ⁵⁶Ni, we suggest that the CSI plus ⁵⁶Ni model is the most promising model. Assuming that the CSM is a shell (wind), the masses of the ejecta, the CSM, and the ⁵⁶Ni are ${15.79}_{-4.77}^{+5.44}$${{\rm{M}}}_{\odot }$ (${14.18}_{-1.64}^{+1.81}$M_⊙), ${0.84}_{-0.10}^{+0.13}$M_⊙ (${0.88}_{-0.12}^{+0.11}$M_⊙), and ${0.32}_{-0.11}^{+0.11}$M_⊙ (${0.16}_{-0.08}^{+0.13}$M_⊙), respectively. The inferred ejecta masses are consistent with the scenario that the progenitors of SNe Ibn are massive Wolf–Rayet stars. Adopting the shell CSM scenario, the shell might be expelled by an eruption of the progenitor just ∼17–167 days prior to the SN explosion; for the wind scenario, the inferred mass-loss rate of the wind is ∼8.0 M_⊙ yr⁻¹, indicating that the wind is a "super-wind" having an extremely high mass-loss rate.

Recent observations demonstrated that emerging flux regions, which constitute the early stage of solar active regions, consist of emergence of numerous small-scale magnetic elements. They in turn interact, merge, and form mature sunspots. However, observations of fine magnetic structures on photosphere with subarcsecond resolution are very rare due to limitations of observing facilities. In this work, taking advantage of the high resolution of the 1.6 m Goode Solar Telescope, we jointly analyze vector magnetic fields, continuum images, and Hα observations of NOAA AR 12665 on 2017 July 13, with the goal of understanding the signatures of small-scale flux emergence, as well as their atmospheric responses as they emerge through multiple heights in the photosphere and chromosphere. Under such a high resolution of 01–02, our results confirm two kinds of small-scale flux emergence: magnetic flux sheet emergence associated with the newly forming granules, and the traditional magnetic flux loop emergence. With direct imaging in the broadband TiO, we observe that both types of flux emergence are associated with darkening of granular boundaries, while only flux sheets elongate granules along the direction of emerging magnetic fields and expand laterally. With a life span of 10 ∼ 15 minutes, the total emerged vertical flux is on the order of  10¹⁸ Mx for both types of emergence. The magnitudes of the vertical and horizontal fields are comparable in the flux sheets, while the former is stronger in flux loops. Hα observations reveal transient brightenings in the wings in the events of magnetic loop emergence, which are most probably the signatures of Ellerman bombs.

Interstellar complex organic molecules are assumed to be mainly formed on dust–grain surfaces. However, neutral gas-phase reactions in the interstellar medium can play an important role. In this paper, by investigating the reaction between aldehydes and the cyano radical, we show that both formaldehyde (CH₂O) and acetaldehyde (CH₃CHO) can lead to the formation of formyl cyanide (HCOCN). Owing to accurate quantum-chemical computations followed by rate constant evaluations, we have been able to suggest and validate an effective mechanism for the formation of HCOCN, one of the molecules observed in the ISM. Quite interestingly, the mechanism starting from CH₂O is very effective at a low temperature, while that involving CH₃CHO becomes more efficient at temperatures above 200 K.

Magnetic reconnection is a fundamental process that quickly releases magnetic energy stored in a plasma. Identifying from simulation outputs where reconnection is taking place is nontrivial and, in general, has to be performed by human experts. Hence, it would be valuable if such an identification process could be automated. Here, we demonstrate that a machine-learning algorithm can help to identify reconnection in 2D simulations of collisionless plasma turbulence. Using a Hybrid Vlasov Maxwell model, a data set containing over 2000 potential reconnection events was generated and subsequently labeled by human experts. We test and compare two machine-learning approaches with different configurations on this data set. The best results are obtained with a convolutional neural network combined with an "image cropping" step that zooms in on potential reconnection sites. With this method, more than 70% of reconnection events can be identified correctly. The importance of different physical variables is evaluated by studying how they affect the accuracy of predictions. Finally, we also discuss various possible causes for wrong predictions from the proposed model.