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<jats:title>Abstract</jats:title> <jats:p>A classical paradox in high-mass star formation is that powerful radiation pressure can halt accretion, preventing further growth of a central star. Disk accretion has been proposed to solve this problem, but the disks and the accretion process in high-mass star formation are poorly understood. We executed high-resolution (<jats:italic>R</jats:italic> = 35,000–70,000) iSHELL spectroscopy in <jats:italic>K</jats:italic>-band for 11 high-mass protostars. Br-<jats:italic>γ</jats:italic> emission was observed toward eight sources, and the line profiles for most of these sources are similar to those of low-mass PMS stars. Using an empirical relationship between the Br-<jats:italic>γ</jats:italic> and accretion luminosities, we tentatively estimate disk accretion rates ranging from ≲10<jats:sup>−8</jats:sup> and ∼10<jats:sup>−4</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. These low-mass-accretion rates suggest that high-mass protostars gain more mass via episodic accretion as proposed for low-mass protostars. Given the detection limits, CO overtone emission (<jats:italic>v</jats:italic> = 2−0 and 3−1), likely associated with the inner disk region (<jats:italic>r</jats:italic> ≪ 100 au), was found toward two sources. This low-detection rate compared with Br-<jats:italic>γ</jats:italic> emission is consistent with previous observations. Ten out of the 11 sources show absorption at the <jats:italic>v</jats:italic> = 0–2 R(7) − R(14) CO R-branch. Most of them are either blueshifted or redshifted, indicating that the absorption is associated with an outflow or an inflow with a velocity of up to ∼50 km s<jats:sup>−1</jats:sup>. Our analysis indicates that the absorption layer is well thermalized (and therefore <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{{{\rm{H}}}_{2}}\gtrsim {10}^{6}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabee88ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> cm<jats:sup>−3</jats:sup>) at a single temperature of typically 100–200 K, and located within 200–600 au of the star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The ubiquitous relativistic jet phenomena associated with black holes play a major role in high and very-high-energy (VHE) astrophysics. In particular, observations have demonstrated that blazars show VHE emission with time variability from days to minutes (in the gigaelectronvolt and teraelectronvolt bands), implying very compact emission regions. The real mechanism of the particle acceleration process responsible for this emission is still being debated, but magnetic reconnection has lately been discussed as a strong potential candidate. In this work, we present the results of three-dimensional special relativistic magnetohydrodynamic simulations of the development of reconnection events driven by turbulence induced by current-driven kink instability along a relativistic jet. We have performed a systematic identification of all reconnection regions in the system, characterizing their local magnetic field topology and quantifying the reconnection rates. We obtained average rates of 0.051 ± 0.026 (in units of Alfvén speed), which are comparable to the predictions of the theory of turbulence-induced fast reconnection. A detailed statistical analysis also demonstrated that the fast reconnection events follow a log-normal distribution, which is a signature of its turbulent origin. To probe the robustness of our method, we have applied our results to the blazar Mrk 421. Building a synthetic light curve from the integrated magnetic reconnection power, we evaluated the time variability from a power spectral density analysis, obtaining good agreement with observations in the gigaelectronvolt band. This suggests that turbulent fast magnetic reconnection can be a possible process behind the high-energy emission variability phenomena observed in blazars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the hydrogen ionization instability mechanism in the context of low-mass X-ray binaries with a black hole as a central object. We make numerical calculations of the predicted outbursts’ light curves and compare them to the data observed by X-ray satellites. The comparison to the data is done for five sources observed by RXTE/ASM (XTE J1550−564, 4U 1630−472, XTE J1859+226, GX 339-4, XTE J1818−245) and one source observed by MAXI (MAXI J1659−152). The aim of this paper is to show that the hydrogen ionization instability operating in an accretion disk is responsible for the shape of outbursts observed in low-mass X-ray binaries. From the data fitting process, we put tight constraints on global source parameters such as black hole mass and disk accretion rate. The influence of chemical composition on the overall analysis is also shown. In the case of each outburst, we found the overall bolometric light curve shape that qualitatively matches the data. We were able to model the main outburst and secondary reflare often seen in the data, the latter one caused by the presence of metals in disk gas. In the case of 4U 1630−472, we analyzed two outbursts, which allowed us to put tight constraints on the black hole mass of 4 ± 0.5<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and on the accretion rate of <jats:inline-formula> <jats:tex-math> <?CDATA ${2}_{-0.2}^{+1.4}\times {10}^{-8}{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabee79ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> yr<jats:sup>−1</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on results by recent surveys, the number of bright quasars at redshifts <jats:italic>z</jats:italic> &gt; 3 is being constantly revised upward. The current consensus is that at bright magnitudes (<jats:italic>M</jats:italic> <jats:sub>1450</jats:sub> ≤ −27) the number densities of such sources could have been underestimated by a factor of 30%–40%. In the framework of the QUBRICS survey, we identified 58 bright QSOs at 3.6 ≤ <jats:italic>z</jats:italic> ≤ 4.2, with magnitudes <jats:italic>i</jats:italic> <jats:sub>psf</jats:sub> ≤ 18, in an area of 12400 deg<jats:sup>2</jats:sup>. The uniqueness of our survey is underlined by the fact that it allows us, for the first time, to extend the sampled absolute magnitude range up to <jats:italic>M</jats:italic> <jats:sub>1450</jats:sub> = −29.5. We derived a bright-end slope of <jats:italic>β</jats:italic> = −4.025 and a space density at 〈<jats:italic>M</jats:italic> <jats:sub>1450</jats:sub>〉 = −28.75 of 2.61 × 10<jats:sup>−10</jats:sup> Mpc<jats:sup>−3</jats:sup> comoving, after taking into account the estimated incompleteness of our observations. Taking into account the results of fainter surveys, active galactic nuclei (AGNs) brighter than <jats:italic>M</jats:italic> <jats:sub>1450</jats:sub> = −23 could produce at least half of the ionizing emissivity at <jats:italic>z</jats:italic> ∼ 4. Considering a mean escape fraction of 0.7 for the QSO and AGN population, combined with a mean free path of 41.3 proper Mpc at <jats:italic>z</jats:italic> = 3.9, we derive a photoionization rate of <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{Log}}({\rm{\Gamma }}\left[{{\rm{s}}}^{-1}\right])=-{12.17}_{-0.07}^{+0.13}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabedb5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, produced by AGNs at <jats:italic>M</jats:italic> <jats:sub>1450</jats:sub> &lt; −18, that is, ∼100% of the measured ionizing background at <jats:italic>z</jats:italic> ∼ 4.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Mass loss is an important activity for red supergiants (RSGs) and can influence their evolution and final fate. Previous estimations of mass-loss rates (MLRs) of RSGs exhibit significant dispersion due to differences in method and the incompleteness of samples. With the improved quality and depth of surveys including the UKIRT/WFCAM observations in the near-infrared, and LGGS and PS1 in the optical, a rather complete sample of RSGs is identified in M31 and M33 according to their brightness and colors. For about 2000 objects in either galaxy from this largest ever sample, the MLR is derived by fitting the observational optical-to-mid-infrared spectral energy distribution with the DUSTY code of a 1D dust radiative transfer model. The average MLR of RSGs is found to be around 2.0 × 10<jats:sup>−5</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> with a gas-to-dust ratio of 100, which yields a total contribution to the interstellar dust from RSGs of about 1.1 × 10<jats:sup>−3</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> in M31 and 6.0 × 10<jats:sup>−4</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> in M33, a non-negligible source in comparison with evolved low-mass stars. The MLRs are divided into three types by the dust species, i.e., amorphous silicate, amorphous carbon, and optically thin, and the relations between MLR and stellar parameters, infrared flux, and colors are discussed and compared with previous works for the silicate and carbon dust groups.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a reflected reprocessing model to study the thermal lag–wavelength relationship in the AGN accretion disk. The main radiation produced from the corona assumed with the lamppost geometry on the axis of the black hole irradiates the accretion disk to affect the temperature structure via reflection processes. Considering the thermal emission of the disk responded to coronal irradiation, we obtain the lag–wavelength relationship of the disk emission by calculating the response function. We then fit the observed data of four Seyfert 1–1.5 galaxies, NGC4151 , Mrk509, NGC5548, and NGC4593, to test the reflected reprocessing model compared with the X-ray spectrum fitting, and the main results present as follows: (I) The actual geometry of the disk corona is more complex than the lamppost. (II) The option of the reference band is sensitive to fitting the observed time lags. (III) The intrinsic bolometric luminosity is larger than the observed luminosity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use the IllustrisTNG (TNG) simulations of galaxy formation to measure the velocity dispersion profiles of dark matter and stars in Milky Way–mass, galaxy group, and cluster-scale dark matter halos. The mean profiles calculated from both tracers are similar in shape, exhibiting a large halo-to-halo scatter around the average profile. The so-called “splashback” radius demarcates the outer boundary of the halo, and manifests as a kink in the velocity dispersion profile, located on average between ∼1.0–1.5<jats:italic>r</jats:italic> <jats:sub>200<jats:italic>m</jats:italic> </jats:sub>, where <jats:italic>r</jats:italic> <jats:sub>200<jats:italic>m</jats:italic> </jats:sub> is the radius within which the density of the halo equals 200 times the background density of the universe. We find that this location may also be identified as the radius at which the (stacked) dispersion profile drops to 60% of its peak value (for line-of-sight motions in TNG halos). We further show that the scatter in the dispersion profiles may be attributed to the variations in the assembly history of the host halos. In particular, this segregates the profile into two regimes: one within ∼0.1<jats:italic>r</jats:italic> <jats:sub>200<jats:italic>m</jats:italic> </jats:sub>, where the scatter is set by the early assembly history of the halo; and the other beyond this radius, where the scatter is influenced more strongly by its late-time assembly. Finally, we show that a two-parameter model can be used to fit the measured velocity dispersion profiles and the fit parameters can be related directly to two fundamental halo properties: mass and concentration. We describe a simple model that allows us to express the stellar velocity dispersion profile in terms of these halo properties only.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of a circumstellar debris disk viewed nearly edge-on and associated with the young, K1 star BD+45° 598 using high-contrast imaging at 2.2 <jats:italic>μ</jats:italic>m obtained at the W.M. Keck Observatory. We detect the disk in scattered light with a peak significance of ∼5<jats:italic>σ</jats:italic> over three epochs, and our best-fit model of the disk is an almost edge-on ∼70 au ring, with inclination angle ∼87°. Using the NOEMA interferometer at the Plateau de Bure Observatory operating at 1.3 mm, we find resolved continuum emission aligned with the ring structure seen in the 2.2 <jats:italic>μ</jats:italic>m images. We estimate a fractional infrared luminosity of <jats:italic>L</jats:italic> <jats:sub>IR</jats:sub>/<jats:italic>L</jats:italic> <jats:sub>tot</jats:sub> <jats:inline-formula> <jats:tex-math> <?CDATA $\simeq \,{6}_{-1}^{+2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec6eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> × 10<jats:sup>−4</jats:sup>, higher than that of the debris disk around AU Mic. Several characteristics of BD+45° 598, such as its galactic space motion, placement in a color–magnitude diagram, and strong presence of lithium, are all consistent with its membership in the <jats:italic>β</jats:italic> Pictoris Moving Group with an age of 23 ± 3 Myr. However, the galactic position for BD+45° 598 is slightly discrepant from previously known members of the <jats:italic>β</jats:italic> Pictoris Moving Group, possibly indicating an extension of members of this moving group to distances of at least 70 pc. BD+45° 598 appears to be an example from a population of young circumstellar debris systems associated with newly identified members of young moving groups that can be imaged in scattered light, key objects for mapping out the early evolution of planetary systems from ∼10–100 Myr. This target will also be ideal for northern-hemisphere, high-contrast imaging platforms to search for self-luminous, planetary mass companions residing in this system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Molecular hydrogen (H<jats:sub>2</jats:sub>) is the dominant molecular species in the vast majority of interstellar environments and it plays a crucial role as a radiative coolant. In photodissociation regions (PDRs), it is one of the primary emitters in the near- to mid-infrared, which is due to lines originating from highly excited levels. The sparseness of H<jats:sub>2</jats:sub> collisional data for rotational levels <jats:italic>J</jats:italic> ≥ 9, particularly for H<jats:sub>2</jats:sub>–H<jats:sub>2</jats:sub> collisions, has limited nonlocal thermal equilibrium (NLTE) studies in ultraviolet-irradiated regions. Utilizing new calculations for para- and ortho-H<jats:sub>2</jats:sub> high rotational collisional rate coefficients colliding with H<jats:sub>2</jats:sub> (up to the maximum value for <jats:italic>v</jats:italic> = 0: <jats:italic>J</jats:italic> = 31), existing data for H<jats:sub>2</jats:sub>–H and H<jats:sub>2</jats:sub>–He collisions, and approximate scaling relations for missing collisional data, we investigate the excitation properties of H<jats:sub>2</jats:sub> in a range of astrophysical environments, with the focus on PDRs (including benchmark PDR models and the Orion Bar). In these NLTE models, H<jats:sub>2</jats:sub> emission is illustrated and shown as a diagnostic for physical conditions, such as temperature and density. Furthermore, we demonstrated the effect of updates in the collisional rates on the modeling results of H<jats:sub>2</jats:sub> excitation. The resulting data sets of H<jats:sub>2</jats:sub> collisional data should find wide application to other molecular environments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the likely GeV <jats:italic>γ</jats:italic>-ray emission from the composite supernova remnant (SNR) COMP G327.1+1.1 by analyzing ∼12.2 yr of the Fermi Large Area Telescope (Fermi-LAT) Pass 8 data. We found the features of its spectrum and luminosity are well consistent with those of the observed COMP SNRs in the Milky Way. Moreover, the position of the source matches those in radio and TeV energy bands; we propose that the <jats:italic>γ</jats:italic>-ray source is likely to be a GeV counterpart of COMP G327.1+1.1. Considering the case of the association from COMP G327.1+1.1 and the <jats:italic>γ</jats:italic>-ray source, we interpreted its broadband spectral energy distribution (SED) by using three simple stationary models including one-zone and two-zone leptonic models and a one-zone leptohadronic model. We found that the simple two-zone model dominated by leptons can better explain its SED. More high-energy data are expected to firmly confirm the association between the <jats:italic>γ</jats:italic>-ray source and COMP G327.1+1.1 in the future.</jats:p>