Table of contents

We present detections of the CO(4–3) and [C i] 609 μm spectral lines, as well as the dust continuum at 480.5 GHz (rest frame), in 3C 368, a Fanaroff–Riley class II (FR-II) galaxy at redshift (z) 1.131. 3C 368 has a large stellar mass, ∼ 3.6 × 10¹¹M_⊙, and is undergoing an episode of vigorous star formation, at a rate of ∼ 350 M_⊙ yr⁻¹, and active galactic nucleus activity, with radio-emitting lobes extended over ∼ 73 kpc. Our observations allow us to inventory the molecular-gas reservoirs in 3C 368 by applying three independent methods: (1) using the CO(4–3)-line luminosity, excitation state of the gas, and an α_CO conversion factor, (2) scaling from the [C i]-line luminosity, and (3) adopting a gas-to-dust conversion factor. We also present gas-phase metallicity estimates in this source, both using far-infrared fine-structure lines together with radio free–free continuum emission and independently employing the optical [O iii] 5007 Å and [O ii] 3727 Å lines (R₂₃ method). Both methods agree on a subsolar gas-phase metallicity of ∼ 0.3 Z_⊙. Intriguingly, comparing the molecular-gas mass estimated using this subsolar metallicity, M_gas ∼ 6.4 × 10¹⁰M_⊙, to dust-mass estimates from multicomponent spectral energy distribution modeling, M_dust ∼ 1.4 × 10⁸M_⊙, yields a gas-to-dust ratio within ∼ 15% of the accepted value for a metallicity of 0.3 Z_⊙. The derived gas mass puts 3C 368 on a par with other galaxies at z ∼ 1 in terms of specific star formation rate and gas fraction. However, it does not explain how a galaxy can amass such a large stellar population while maintaining such a low gas-phase metallicity. Perhaps 3C 368 has recently undergone a merger, accreting pristine molecular gas from an external source.

We perform GR-MHD simulations of outflow launching from thin accretion disks. As in the nonrelativistic case, resistivity is essential for the mass loading of the disk wind. We implemented resistivity in the ideal GR-MHD code HARM3D, extending previous works for larger physical grids, higher spatial resolution, and longer simulation time. We consider an initially thin, resistive disk orbiting the black hole, threaded by a large-scale magnetic flux. As the system evolves, outflows are launched from the black hole magnetosphere and the disk surface. We mainly focus on disk outflows, investigating their MHD structure and energy output in comparison with the Poynting-dominated black hole jet. The disk wind encloses two components—a fast component dominated by the toroidal magnetic field and a slower component dominated by the poloidal field. The disk wind transitions from sub- to super-Alfvénic speed, reaching velocities ≃0.1c. We provide parameter studies varying spin parameter and resistivity level and measure the respective mass and energy fluxes. A higher spin strengthens the B_ϕ-dominated disk wind along the inner jet. We disentangle a critical resistivity level that leads to a maximum matter and energy output for both, resulting from the interplay between reconnection and diffusion, which in combination govern the magnetic flux and the mass loading. For counterrotating black holes the outflow structure shows a magnetic field reversal. We estimate the opacity of the innermost accretion stream and the outflow structure around it. This stream may be critically opaque for a lensed signal, while the axial jet funnel remains optically thin.

The self-regulation of cosmic-ray (CR) transport in the interstellar and intracluster media has long been viewed through the lenses of linear and quasi-linear kinetic plasma physics. Such theories are believed to capture the essence of CR behavior in the presence of self-generated turbulence but cannot describe potentially critical details arising from the nonlinearities of the problem. We utilize the particle-in-cell numerical method to study the time-dependent nonlinear behavior of the gyroresonant streaming instabilities, self-consistently following the combined evolution of particle distributions and self-generated wave spectra in one-dimensional periodic simulations. We demonstrate that the early growth of instability conforms to the predictions from linear physics, but that the late-time behavior can vary depending on the properties of the initial CR distribution. We emphasize that the nonlinear stages of instability depend strongly on the initial anisotropy of CRs—highly anisotropic CR distributions do not efficiently reduce to Alfvénic drift velocities, owing to reduced production of left-handed resonant modes. We derive estimates for the wave amplitudes at saturation and the timescales for nonlinear relaxation of the CR distribution and then demonstrate the applicability of these estimates to our simulations. Bulk flows of the background plasma due to the presence of resonant waves are observed in our simulations, confirming the microphysical basis of CR-driven winds.

The width of the broad emission lines in quasars is commonly characterized by either the FWHM or the square root of the second moment of the line profile (σ_line) and used as an indicator of the virial velocity of the broad-line region (BLR) in the estimation of black hole (BH) mass. We measure FWHM and σ_line for Hα, Hβ, and Mg ii broad lines in both the mean and rms spectra of a large sample of quasars from the Sloan Digital Sky Survey Reverberation Mapping project. We introduce a new quantitative recipe to measure σ_line that is reproducible, is less susceptible to noise and blending in the wings, and scales with the intrinsic width of the line. We compare the four definitions of line width (FWHM and σ_line in mean and rms spectra, respectively) for each of the three broad lines and among different lines. There are strong correlations among different width definitions for each line, providing justification for using the line width measured in single-epoch spectroscopy as a virial velocity indicator. There are also strong correlations among different lines, suggesting that alternative lines to Hβ can be used to estimate virial BH masses. We further investigate the correlations between virial BH masses using different line width definitions and the stellar velocity dispersion of the host galaxies and the dependence of line shape (characterized by the ratio FWHM/σ_line) on physical properties of the quasar. Our results provide further evidence that FWHM is more sensitive to the orientation of a flattened BLR geometry than σ_line, but the overall comparison between the virial BH mass and host stellar velocity dispersion does not provide conclusive evidence that one particular width definition is significantly better than the others.

A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array for five luminous or ultraluminous infrared galaxies gives a slope for the Kennicutt–Schmidt (KS) relation equal to ${1.74}_{-0.07}^{+0.09}$ for gas surface densities Σ_mol > 10³M_⊙ pc⁻² and an assumed constant CO-to-H₂ conversion factor. The velocity dispersion of the CO line, σ_v, scales approximately as the inverse square root of Σ_mol, making the empirical gas scale height determined from $H\sim 0.5{\sigma }^{2}/(\pi G{{\rm{\Sigma }}}_{\mathrm{mol}})$ nearly constant, 150–190 pc, over 1.5 orders of magnitude in Σ_mol. This constancy of H implies that the average midplane density, which is presumably dominated by CO-emitting gas for these extreme star-forming galaxies, scales linearly with the gas surface density, which in turn implies that the gas dynamical rate (the inverse of the freefall time) varies with ${{\rm{\Sigma }}}_{\mathrm{mol}}^{1/2}$, thereby explaining most of the super-linear slope in the KS relation. Consistent with these relations, we also find that the mean efficiency of star formation per freefall time is roughly constant, 5%–7%, and the gas depletion time decreases at high Σ_mol, reaching only ∼16 Myr at Σ_mol ∼ 10⁴M_⊙ pc⁻². The variation of σ_v with Σ_mol and the constancy of H are in tension with some feedback-driven models, which predict σ_v to be more constant and H to be more variable. However, these results are consistent with simulations in which large-scale gravity drives turbulence through a feedback process that maintains an approximately constant Toomre Q instability parameter.

We present a detailed Monte Carlo model of observational errors in observed galaxy scaling relations to recover the intrinsic (cosmic) scatter driven by galaxy formation and evolution processes. We apply our method to the stellar radial acceleration relation (RAR), which compares the local observed radial acceleration to the local Newtonian radial acceleration computed from the stellar mass distribution. The stellar and baryonic RAR are known to exhibit similar scatter. Lelli+2017 (L17) studied the baryonic RAR using a sample of 153 spiral galaxies and inferred a negligible intrinsic scatter. If true, a small scatter might challenge the ΛCDM galaxy formation paradigm, possibly favoring a modified Newtonian dynamics interpretation. The intrinsic scatter of the baryonic RAR is predicted by modern ΛCDM simulations to be ∼0.06–0.08 dex, contrasting with the null value reported by L17. We have assembled a catalog of structural properties with over 2500 spiral galaxies from six deep imaging and spectroscopic surveys (called the "Photometry and Rotation curve OBservations from Extragalactic Surveys") to quantify the intrinsic scatter of the stellar RAR and other scaling relations. The stellar RAR for our full sample has a median observed scatter of 0.17 dex. We use our Monte Carlo method, which accounts for all major sources of measurement uncertainty, to infer a contribution of 0.12 dex from the observational errors. The intrinsic scatter of the stellar RAR is thus estimated to be 0.11 ± 0.02 dex, in agreement with, though slightly greater than, current ΛCDM predictions.

The Interface Region Imaging Spectrograph (IRIS) has observed bright spots at the transition region footpoints associated with heating in the overlying loops, as observed by coronal imagers. Some of these brightenings show significant blueshifts in the Si iv line at 1402.77 Å ($\mathrm{log}T[{\rm{K}}]\approx 4.9$). Such blueshifts cannot be reproduced by coronal loop models assuming heating by thermal conduction only, but are consistent with electron beam heating, highlighting for the first time the possible importance of nonthermal electrons in the heating of nonflaring active regions. Here we report on the coronal counterparts of these brightenings observed in the hot channels of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We show that the IRIS bright spots are the footpoints of very hot and transient coronal loops that clearly experience strong magnetic interactions and rearrangements, thus confirming the impulsive nature of the heating and providing important constraints for their physical interpretation.

We examine the effects of supermassive black hole (SMBH) feedback on the circumgalactic medium (CGM) using a cosmological hydrodynamic simulation (Romulus25) and a set of four zoom-in "genetically modified" Milky-Way–mass galaxies sampling different evolutionary paths. By tracing the distribution of metals in the CGM, we show that O vi is a sensitive indicator of SMBH feedback. First, we calculate the column densities of O vi in simulated Milky-Way–mass galaxies and compare them with observations from the COS-Halos Survey. Our simulations show column densities of O vi in the CGM consistent with those of COS-Halos star-forming and quenched galaxies. These results contrast with those from previous simulation studies which typically underproduce CGM column densities of O vi. We determine that a galaxy's star formation history and assembly record have little effect on the amount of O vi in its CGM. Instead, column densities of O vi are closely tied to galaxy halo mass and BH growth history. The set of zoom-in, genetically modified Milky-Way–mass galaxies indicates that the SMBH drives highly metal-enriched material out into its host galaxy's halo, which in turn elevates the column densities of O vi in the CGM.

The role of gas accretion in galaxy evolution is still a matter of debate. The presence of inflows of metal-poor gas that trigger star formation bursts of low metallicity has been proposed as an explanation for the local anticorrelation between star formation rate (SFR) and gas-phase metallicity (Z_g) found in the literature. In the present study, we show how the anticorrelation is also present as part of a diversified range of behaviors for a sample of more than 700 nearby spiral galaxies from the SDSS-IV MaNGA survey. We have characterized the local relation between SFR and Z_g after subtracting the azimuthally averaged radial profiles of both quantities. Of the analyzed galaxies, 60% display an SFR–Z_g anticorrelation, with the remaining 40% showing no correlation (19%) or positive correlation (21%). Applying a random forest machine-learning algorithm, we find that the slope of the correlation is mainly determined by the average gas-phase metallicity of the galaxy. Galaxy mass, g − r colors, stellar age, and mass density seem to play a less significant role. This result is supported by the performed second-order polynomial regression analysis. Thus, the local SFR–Z_g slope varies with the average metallicity, with the more metal-poor galaxies presenting the lowest slopes (i.e., the strongest SFR–Z_g anticorrelations), and reversing the relation for more metal-rich systems. Our results suggest that external gas accretion fuels star formation in metal-poor galaxies, whereas in metal-rich systems, the gas comes from previous star formation episodes.

We report on ≈035 (≈2kpc) resolution observations of the [C ii] and dust continuum emission from five z > 6 quasar host–companion galaxy pairs obtained with the Atacama Large Millimeter/submillimeter Array. The [C ii] emission is resolved in all galaxies, with physical extents of 3.2–5.4 kpc. The dust continuum is on-average 40% more compact, which results in larger [C ii] deficits in the center of the galaxies. However, the measured [C ii] deficits are fully consistent with those found at lower redshifts. Four of the galaxies show [C ii] velocity fields that are consistent with ordered rotation, while the remaining six galaxies show no clear velocity gradient. All galaxies have high (∼80−200 km s⁻¹) velocity dispersions, consistent with the interpretation that the interstellar medium (ISM) of these high-redshift galaxies is turbulent. By fitting the galaxies with kinematic models, we estimate the dynamical mass of these systems, which ranges between (0.3 − >5.4) × 10¹⁰M_⊙. For the three closest-separation galaxy pairs, we observe dust and [C ii] emission from gas in between and surrounding the galaxies, which is an indication that tidal interactions are disturbing the gas in these systems. Although gas exchange in these tidal interactions could power luminous quasars, the existence of quasars in host galaxies without nearby companions suggests that tidal interactions are not the only viable method for fueling their active centers. These observations corroborate the assertion that accreting supermassive black holes do not substantially contribute to the [C ii] and dust continuum emission of the quasar host galaxies, and showcase the diverse ISM properties of galaxies when the universe was less than one billion years old.

Although the ${}^{2}{{\rm{P}}}_{3/2}-{}^{2}{{\rm{P}}}_{1/2}$ transition of [C ii] at λ ≃  158 $\,\mu {\rm{m}}$ is known to be an excellent tracer of active star formation, we still do not have a complete understanding of where within star formation regions the emission originates. Here, we use SOFIA upGREAT observations of [C ii] emission toward the H ii region complex Sh2-235 (S235) to better understand in detail the origin of [C ii] emission. We complement these data with a fully sampled Green Bank Telescope radio recombination line map tracing the ionized hydrogen gas. About half of the total [C ii] emission associated with S235 is spatially coincident with ionized hydrogen gas, although spectroscopic analysis shows little evidence that this emission is coming from the ionized hydrogen volume. Velocity-integrated [C ii] intensity is strongly correlated with Wide-field Infrared Survey Explorer (WISE) 12 $\,\mu {\rm{m}}$ intensity across the entire complex, indicating that both trace ultraviolet radiation fields. The 22 $\,\mu {\rm{m}}$ and radio continuum intensities are only correlated with [C ii] intensity in the ionized hydrogen portion of the S235 region and the correlations between the [C ii] and molecular gas tracers are poor across the region. We find similar results for emission averaged over a sample of external galaxies, although the strength of the correlations is weaker. Therefore, although many tracers are correlated with the strength of [C ii] emission, only WISE 12 $\,\mu {\rm{m}}$ emission is correlated on small scales of the individual H ii region S235 and also has a decent correlation at the scale of entire range of galaxies. Future studies of a larger sample of Galactic H ii regions would help to determine whether these results are truly representative.

Slitless spectrometers can provide simultaneous imaging and spectral data over an extended field of view, thereby allowing rapid data acquisition for extended sources. In some instances, when the object is greatly extended or the spectral dispersion is too small, there may be locations in the focal plane where emission lines at different wavelengths contribute. It is then desirable to unfold the overlapped regions in order to isolate the contributions from the individual wavelengths. In this paper, we describe a method for such an unfolding, using an inversion technique developed for an extreme ultraviolet imaging spectrometer and coronagraph named the COronal Spectroscopic Imager in the EUV (COSIE). The COSIE spectrometer wavelength range (18.6–20.5 nm) contains a number of strong coronal emission lines and several density sensitive lines. We focus on optimizing the unfolding process to retrieve emission measure maps at constant temperature, maps of spectrally pure intensity in the Fe xii and Fe xiii lines, and density maps based on both Fe xii and Fe xiii diagnostics.

The signal measured by an astronomical spectrometer may be due to radiation from a multi-component mixture of plasmas with a range of physical properties (e.g., temperature, Doppler velocity). Confusion between multiple components may be exacerbated if the spectrometer sensor is illuminated by overlapping spectra dispersed from different slits, with each slit being exposed to radiation from a different portion of an extended astrophysical object. We use a compressed sensing method to robustly retrieve the different components. This method can be adopted for a variety of spectrometer configurations, including single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer mission), and slot spectrometers (which produce overlappograms).

Galaxies in pairs show enhanced star formation (SF) compared to their counterparts in isolation, which is often explained by the tidal effect of neighboring galaxies. Recent observations, however, reported that galaxies paired with early-type neighbors do not undergo the SF enhancement. Here we revisit the influence of neighbors using a large sample of paired galaxies from the Sloan Digital Sky Survey and a carefully constructed control sample of isolated counterparts. We find that star-forming neighbors enhance SF, and even more so for more star-forming (and closer) neighbors, which can be attributed to collisions of interstellar medium (ISM) leading to SF. We further find that, contrary to the anticipated tidal effect, quiescent neighbors quench SF, and even more so for more quiescent (and closer) neighbors. This seems to be due to removal of gas reservoirs via ram pressure stripping and gas accretion cut off by hot gas halos of quiescent neighbors, on top of their paucity of ISM to collide to form stars. Our findings, especially the intimate connection of SF to the status and strength of neighbors' SF, imply that the hydrodynamic mechanisms, along with the tidal effect, play a crucial role during the early phase of galactic interactions.

The Chree method of analysis is a useful tool employed in solar–terrestrial studies. In a bid to fine-tune the results obtained by the technique, some areas of improvements, especially the statistical test of significance, have been pointed out. Recently, Okike & Umahi spotted another pitfall in the technique with regard to the type of neutron monitor data used. The present work suggests that harmonic analysis is required to deal with galactic cosmic-ray (CR) signals, composed of different periodicities, cycles, and short-term random fluctuations. It is equally demonstrated that an R software program could be adapted to calculate the magnitude and timing of the sudden and rapid depressions (referred to as Forbush decreases [FDs]) in the high-frequency term of the transformed signal. Our results, in agreement with those of the IZMIRAN group, suggest that large FDs might not be as rare as are claimed by the numerous solar–terrestrial superposition analyses. The present analysis, in consonance with the global survey method of Belov et al., demonstrates that a sophisticated method is required to select FDs in a large volume of CR data. Thus, the small FD samples, usually employed in solar–terrestrial analyses, might be the reason for the misleading conclusions in some past studies that were investigating solar–climate links.

Coronal jets are transient narrow features in the solar corona that originate from all regions of the solar disk: active regions, quiet Sun, and coronal holes. Recent studies indicate that at least some coronal jets in quiet regions and coronal holes are driven by the eruption of a minifilament following flux cancellation at a magnetic neutral line. We have tested the veracity of that view by examining 60 random jets in quiet regions and coronal holes using multithermal (304, 171, 193, and 211 Å) extreme ultraviolet images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly and line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager. By examining the structure and changes in the magnetic field before, during, and after jet onset, we found that 85% of these jets resulted from a minifilament eruption triggered by flux cancellation at the neutral line. The 60 jets have a mean base diameter of 8800 ± 3100 km and a mean duration of 9 ± 3.6 minutes. These observations confirm that minifilament eruption is the driver and magnetic flux cancellation is the primary trigger mechanism for most coronal hole and quiet region coronal jets.

We present the results of the deep Subaru/FOCAS and Keck/MOSFIRE spectroscopy for four spatially extended [O iii] λλ4959, 5007 sources, dubbed [O iii] blobs, at z = 0.6–0.8 that are originally pinpointed by large-area Subaru imaging surveys. The line diagnostics of the rest-frame optical lines suggests that only one [O iii] blob, OIIIB-3, presents an active galactic nucleus (AGN) signature, indicating that hot gas of the rest of the [O iii] blobs is heated by star formation. One of such star-forming [O iii] blobs, OIIIB-4, at z = 0.838 has an [O iii] equivalent width of 845 ± 27 Å and an [O iii]-to-[O ii] λλ3726, 3729 ratio of [O iii]/[O ii] = 6.5 ± 2.7, which are as high as those of typical Green Peas. The spatially resolved spectrum of OIIIB-4 shows [O iii]/[O ii] = 5–10 over 14 kpc in the entire large [O iii] extended regions of OIIIB-4, unlike the known Green Peas, whose strong [O iii] emission region is compact. Moreover, OIIIB-4 presents no high-ionization emission lines, unlike Green Beans, which have extended [O iii] emission with a type 2 AGN. OIIIB-4 is thus a giant Green Pea, which is a low stellar mass (7 × 10⁷${M}_{\odot }$) galaxy with a very high specific star formation rate (sSFR = 2 × 10² Gyr⁻¹), a high-ionization parameter (q_ion ∼ 3 × 10⁸ cm s⁻¹), and a low metallicity similar to those of Green Peas. Neither an AGN light echo nor a fast radiative shock likely takes place owing to the line diagnostics for spatially resolved components of OIIIB-4 and no detections of He iiλ4686 or [Ne v] λλ3346, 3426 lines that are fast radiative shock signatures. There is a possibility that the spatially extended [O iii] emission of OIIIB-4 is originated from outflowing gas produced by the intense star formation in a density-bounded ionization state.

Renzini wrote an influential critique of "overshooting" in mixing-length theory (MLT), as used in stellar evolution codes, and concluded that three-dimensional fluid dynamical simulations were needed. Such simulations are now well tested. Implicit large eddy simulations connect large-scale stellar flow to a turbulent cascade at the grid scale, and allow the simulation of turbulent boundary layers, with essentially no assumptions regarding flow except the number of computational cells. Buoyant driving balances turbulent dissipation for weak stratification, as in MLT, but with the dissipation length replacing the mixing length. The turbulent kinetic energy in our computational domain shows steady pulses after 30 turnovers, with no discernible diminution; these are caused by the necessary lag in turbulent dissipation behind acceleration. Interactions between coherent turbulent structures give multi-modal behavior, which drives intermittency and fluctuations. These cause mixing, which may justify use of the instability criterion of Schwarzschild rather than the Ledoux. Chaotic shear flow of turning material at convective boundaries causes instabilities that generate waves and sculpt the composition gradients and boundary layer structures. The flow is not anelastic; wave generation is necessary at boundaries. A self-consistent approach to boundary layers can remove the need for ad hoc procedures of "convective overshooting" and "semi-convection." In Paper II, we quantify the adequacy of our numerical resolution in a novel way, determine the length scale of dissipation—the "mixing length"—without astronomical calibration, quantify agreement with the four-fifths law of Kolmogorov for weak stratification, and deal with strong stratification.

We show that derivation of Friedmann's equations from the Einstein–Hilbert action, paying attention to the requirements of isotropy and homogeneity during the variation, leads to a different interpretation of pressure than what is typically adopted. Our derivation follows if we assume that the unapproximated metric and Einstein tensor have convergent perturbation series representations on a sufficiently large Robertson–Walker coordinate patch. We find the source necessarily averages all pressures, everywhere, including the interiors of compact objects. We demonstrate that our considerations apply (on appropriately restricted spacetime domains) to the Kerr solution, the Schwarzschild constant-density sphere, and the static de-Sitter sphere. From conservation of stress–energy, it follows that material contributing to the averaged pressure must shift locally in energy. We show that these cosmological energy shifts are entirely negligible for non-relativistic material. In relativistic material, however, the effect can be significant. We comment on the implications of this study for the dark energy problem.

Theoretical studies suggest that a giant planet around the young star MWC 758 could be responsible for driving the spiral features in its circumstellar disk. Here, we present a deep imaging campaign with the Large Binocular Telescope with the primary goal of imaging the predicted planet. We present images of the disk in two epochs in the L' filter (3.8 μm) and a third epoch in the M' filter (4.8 μm). The two prominent spiral arms are detected in each observation, which constitute the first images of the disk at M', and the deepest yet in L' (ΔL' = 12.1 exterior to the disk at 5σ significance). We report the detection of an S/N ∼ 3.9 source near the end of the Southern arm, and, from the source's detection at a consistent position and brightness during multiple epochs, we establish a ∼90% confidence-level that the source is of astrophysical origin. We discuss the possibilities that this feature may be (a) an unresolved disk feature, and (b) a giant planet responsible for the spiral arms, with several arguments pointing in favor of the latter scenario. We present additional detection limits on companions exterior to the spiral arms, which suggest that a ≲4 M_Jup planet exterior to the spiral arms could have escaped detection. Finally, we do not detect the companion candidate interior to the spiral arms reported recently by Reggiani et al., although forward modeling suggests that such a source would have likely been detected.

The self-correlation level contours at 10¹⁰ cm scale reveal a 2D isotropic feature in both the slow solar wind fluctuations and the fast solar wind fluctuations. However, this 2D isotropic feature is obtained based on the assumption of axisymmetry with respect to the mean magnetic field. Whether the self-correlation level contours are still 3D isotropic remains unknown. Here we perform for the first time a 3D self-correlation level contours analysis on the solar wind turbulence. We construct a 3D coordinate system based on the mean magnetic field direction and the maximum fluctuation direction identified by the minimum-variance analysis method. We use data with 1 hr intervals observed by WIND spacecraft from 2005 to 2018. We find, on one hand, in the slow solar wind, the self-correlation level contour surfaces for both the magnetic field and the velocity field are almost spherical, which indicates a 3D isotropic feature. On the other hand, there is a weak elongation in one of the perpendicular directions in the fast solar wind fluctuations. The 3D feature of the self-correlation level contours surfaces cannot be explained by the existing theory.

During the first few hundred days after the explosion, core-collapse supernovae (SNe) emit down-scattered X-rays and gamma-rays originating from radioactive line emissions, primarily from the ⁵⁶Ni → ⁵⁶Co → ⁵⁶Fe chain. We use supernova (SN) models based on three-dimensional neutrino-driven explosion simulations of single stars and mergers to compute this emission and compare the predictions with observations of SN 1987A. A number of models are clearly excluded, showing that high-energy emission is a powerful way of discriminating between models. The best models are almost consistent with the observations, but differences that cannot be matched by a suitable choice of viewing angle are evident. Therefore, our self-consistent models suggest that neutrino-driven explosions are able to produce, in principle, sufficient mixing, although remaining discrepancies may require small changes to the progenitor structures. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor envelope. The main effect of asymmetries is to vary the flux level by a factor of ∼3. For the more asymmetric models, the shapes of the light curves also change. In addition to the models of SN 1987A, we investigate two models of SNe II-P and one model of a stripped-envelope SN IIb. The Type II-P models have observables similar to those of the models of SN 1987A, but the stripped-envelope SN model is significantly more luminous and evolves faster. Finally, we make simple predictions for future observations of nearby SNe.

We present the design and implementation of an automated data calibration and reduction pipeline for very long baseline interferometric (VLBI) observations taken at millimeter wavelengths. These short radio wavelengths provide the best imaging resolution available from ground-based VLBI networks such as the Event Horizon Telescope (EHT) and the Global Millimeter VLBI Array (GMVA) but require specialized processing owing to the strong effects from atmospheric opacity and turbulence, as well as the heterogeneous nature of existing global arrays. The pipeline builds on a calibration suite (HOPS) originally designed for precision geodetic VLBI. To support the reduction of data for astronomical observations, we have developed an additional framework for global phase and amplitude calibration that provides output in a standard data format for astronomical imaging and analysis. The pipeline was successfully used toward the reduction of 1.3 mm observations from the EHT 2017 campaign, leading to the first image of a black hole "shadow" at the center of the radio galaxy M87. In this work, we analyze observations taken at 3.5 mm (86 GHz) by the GMVA, joined by the phased Atacama Large Millimeter/submillimeter Array in 2017 April, and demonstrate the benefits from the specialized processing of high-frequency VLBI data with respect to classical analysis techniques.

SNe Ia could arise from mergers of carbon–oxygen white dwarfs (WDs) triggered by Lidov–Kozai (LK) oscillations in hierarchical triple-star systems. However, predicted merger rates are several orders of magnitude lower than the observed SNe Ia rate. The low predicted rates can be attributed in part to the fact that many potential WD-merger progenitor systems, with high mutual orbital inclination, merge or interact before the WD stage. Recently, evidence was found for the existence of natal kicks imparted on WDs with a typical magnitude of 0.75 km s⁻¹. In triples, kicks change the mutual inclination and in general increase the outer orbit eccentricity, bringing the triple into an active LK regime at late stages and avoiding the issue of pre-WD merger or interaction. Stars passing by the triple can result in similar effects. However, both processes can also disrupt the triple. In this paper, we quantitatively investigate the impact of WD kicks and flybys on the rate of WD mergers using detailed simulations. We find that WD kicks and flybys combine to increase the predicted WD merger rates by a factor of ∼2.5, resulting in a time-integrated rate of ≈1.1 × 10⁻⁴M_⊙⁻¹. Despite the significant boost, the predicted rates are still more than one order of magnitude below the observed rate of ∼10⁻³M_⊙⁻¹. However, many systematic uncertainties still remain in our calculations, in particular the potential contributions from tighter triples, dynamically unstable systems, unbound systems due to WD kicks, and quadruple systems.

We report X-ray data analysis results obtained from Chandra, XMM-Newton, Nuclear Spectroscopic Telescope Array Mission (NuSTAR), and Swift observations of PSR J2032+4127 taken before, during, and after the periastron on 2017 November 13. We found the first clear evidence of a change in the X-ray spectral index over the passage period, thanks to a broad and sensitive spectral coverage by XMM-Newton and NuSTAR. We analyzed the joint XMM-Newton and NuSTAR observation epochs with power-law and broken power-law models. We have obtained changes in spectral parameters before and after the periastron passage for both models. The spectra get softened after the passage. The evolution of the spectral index and break energy before and after the periastron may indicate a change in the physical state of shock-accelerated electrons.

The quasi-thermal components found in many Fermi gamma-ray bursts (GRBs) imply that the photosphere emission indeed contributes to the prompt emission of many GRBs. But whether the observed spectra empirically fitted by the Band function or cutoff power law, especially the spectral and peak energy (E_p) evolutions can be explained by the photosphere emission model alone needs further discussion. In this work, we investigate in detail the time-resolved spectra and E_p evolutions of photospheric emission from a structured jet, with an inner-constant and outer-decreasing angular Lorentz factor profile. Also, a continuous wind with a time-dependent wind luminosity has been considered. We show that the photosphere spectrum near the peak luminosity is similar to the cutoff power-law spectrum. The spectrum can have the observed average low-energy spectral index α ∼ −1, and the distribution of the low-energy spectral index in our photosphere model is similar to that observed (−2 ≲ α ≲ 0). Furthermore, the two kinds of spectral evolutions during the decay phase, separated by the width of the core (θ_c), are consistent with the time-resolved spectral analysis results of several Fermi multi-pulse GRBs and single-pulse GRBs, respectively. Also, for this photosphere model we can reproduce the two kinds of observed E_p evolution patterns rather well. Thus, by considering the photospheric emission from a structured jet, we reproduce the observations well for the GRBs best fitted by the cutoff power-law model for the peak-flux spectrum or the time-integrated spectrum.

In this work, we study the chemical compositions and kinematic properties of six metal-poor stars with [Fe/H] < −2.5 in the Galactic halo. From high-resolution (R ∼ 110,000) spectroscopic observations obtained with the Lick/Automated Planet Finder, we determined individual abundances for up to 23 elements, to quantitatively evaluate our sample. We identify two carbon-enhanced metal-poor stars (J1630+0953 and J2216+0246) without enhancement in neutron-capture elements (CEMP-no stars), while the rest of our sample stars are carbon-intermediate. By comparing the light-element abundances of the CEMP stars with predicted yields from nonrotating zero-metallicity massive-star models, we find that the possible progenitors of J1630+0953 and J2216+0246 could be in the 13–25 M_⊙ mass range, with explosion energies (0.3–1.8) × 10⁵¹ erg. In addition, the detectable abundance ratios of light and heavy elements suggest that our sample stars are likely formed from a well-mixed gas cloud, which is consistent with previous studies. We also present a kinematic analysis, which suggests that most of our program stars likely belong to the inner-halo population, with orbits passing as close as ∼2.9 kpc from the Galactic center. We discuss the implications of these results on the critical constraints on the origin and evolution of CEMP stars, as well as the nature of the Population III progenitors of the lowest-metallicity stars in our Galaxy.

Velocity distributions of particles are key elements in the study of solar wind. The physical mechanisms that regulate their many features are a matter of debate. The present work addresses the subject with a fully analytical method in order to establish the shape of particle velocity distributions in solar wind. The method consists of solving the steady-state kinetic equation for particles and the related fluid equations, with spatial profiles for density and temperature that match general observational data. The model is one-dimensional in configuration-space and two-dimensional in velocity-space, and accounts for large-scale processes, namely, advection, gravity, magnetic mirroring, and the large-scale ambipolar electric field. The findings reported add to the general understanding of regulation of particle distributions in solar wind and to the predictions of their shape in regions restricted for in situ measurements. In particular, the results suggest that fluctuations of temperature at the Sun might play a key role in shaping solar wind velocity distributions via large-scale ambipolar electric field.

Two-and-one-half dimensional particle-in-cell simulations of the forward cascade and dissipation of decaying kinetic Alfvénic turbulence have been carried out on a model of a collisionless, homogeneous, magnetized ion-electron plasma. The uniform background magnetic field ${\boldsymbol{B}}$_o lies parallel to the simulation plane. The simulations were executed as part of the Turbulent Dissipation Challenge. Initial narrowband magnetic fluctuation spectra of kinetic range Alfvén waves undergo a forward cascade to broadband turbulent spectra at shorter wavelengths, at the same time undergoing dissipative transfer of fluctuating field energy to kinetic energy of electrons and ions. The simulations yield Q_i and Q_e, the dimensionless rates of kinetic energy density gain for ions (subscript i) and electrons (subscript e). These are computed for five different initial values of β_i/β_e. For the parameters chosen here, the simulations yield the scaling relation Q_e/Q_i ≈ 2(T_i/T_e)² where T_j represents the initial temperature of the jth species. For all simulation times the kinetic anisotropy of the ions changes monotonically in the sense of greater energy passing from the fluctuations into ion velocities parallel to, rather than perpendicular to, ${\boldsymbol{B}}$_o, suggesting that Landau damping is an important ion dissipation mechanism for kinetic Alfvénic turbulence.

We present extensive ground-based and HubbleSpaceTelescope (HST) photometry of the highly reddened, very nearby SN Ia 2014J in M82, covering the phases from 9 days before to about 900 days after the B-band maximum. SN 2014J is similar to other normal SNe Ia near the maximum light, but it shows flux excess in the B band in the early nebular phase. This excess flux emission can be due to light scattering by some structures of circumstellar materials located at a few 10¹⁷ cm, consistent with a single-degenerate progenitor system or a double-degenerate progenitor system with mass outflows in the final evolution or magnetically driven winds around the binary system. At t ∼ +300 to ∼+500 days past the B-band maximum, the light curve of SN 2014J shows a faster decline relative to the ⁵⁶Ni decay. That feature can be attributed to the significant weakening of the emission features around [Fe iii] λ4700 and [Fe ii] λ5200 rather than the positron escape, as previously suggested. Analysis of the HST images taken at t > 600 days confirms that the luminosity of SN 2014J maintains a flat evolution at the very late phase. Fitting the late-time pseudobolometric light curve with radioactive decay of ⁵⁶Ni, ⁵⁷Ni, and ⁵⁵Fe isotopes, we obtain the mass ratio ⁵⁷Ni/⁵⁶Ni as 0.035 ± 0.011, which is consistent with the corresponding value predicted from the 2D and 3D delayed-detonation models. Combined with early-time analysis, we propose that delayed-detonation through the single-degenerate scenario is most likely favored for SN 2014J.

We report the Atacama Large Millimeter/submillimeter Array observations of the metal-rich host galaxy of superluminous supernova (SLSN) PTF10tpz, a barred spiral galaxy at z = 0.03994. We find the CO(1–0) emission to be confined within the bar of the galaxy. The distribution and kinematics of molecular gas in the host galaxy resemble gas flows along two lanes running from the tips of the bar toward the galaxy center. These gas lanes end in a gaseous structure in the inner region of the galaxy, likely associated with an inner Lindblad resonance. The interaction between the large-scale gas flows in the bar and the gas in the inner region plausibly leads to the formation of massive molecular clouds and consequently massive clusters. This in turn can result in formation of massive stars, and thus the likely progenitor of the SLSN in a young, massive cluster. This picture is consistent with SLSN PTF10tpz being located near the intersection regions of the gas lanes and the inner structure. It is also supported by the high molecular gas surface densities that we find in the vicinity of the SLSN, surface densities that are comparable with those in interacting galaxies or starburst regions in nearby galaxies. Our findings therefore suggest in situ formation of massive stars due to the internal dynamics of the host galaxy and also lend support to high densities being favorable conditions for formation of SLSN progenitors.

A novel model of the solar atmosphere that accounts for partially ionized plasma is developed and used to study the propagation of magnetoacoustic-gravity waves, which are generated by solar granulation. The model includes neutrals in otherwise ionized plasma and therefore the considered waves are two-fluid waves. Numerical simulations of these waves allow computing their cutoff period and its variations in the solar atmosphere. The results of these computations are compared to the observational data collected by Wiśniewska et al. and Kayshap et al., and a good agreement between the theory and observations is obtained. This first theoretical confirmation of the observational data profoundly shows the importance of effects caused by partially ionized plasma on the behavior of waves in the solar atmosphere, and on the origin of solar chromospheric oscillations. It is also suggested that theoretically predicted differences between the behavior of ions and neutrals can be verified by some currently operating solar missions.

There is evidence that protoplanetary disks—including the protosolar one—contain crystalline dust grains on spatial scales where the dust temperature is lower than the threshold value for their formation through thermal annealing of amorphous interstellar silicates. We interpret these observations in terms of an extended, magnetocentrifugally driven disk wind that transports grains from the inner disk—where they are thermally processed by the stellar radiation after being uplifted from the disk surfaces—to the outer disk regions. For any disk radius r, there is a maximum grain size a_max(r) that can be uplifted from that location: grains of size a ≪ a_max are carried away by the wind, whereas those with a ≲ a_max reenter the disk at larger radii. A significant portion of the reentering grains converge to—and subsequently accumulate in—a narrow region just beyond r_max(a), the maximum radius from which grains of size a can be uplifted. We show that this model can account for the inferred crystallinity fractions in classical T Tauri and Herbig Ae disks and for their indicated near constancy after being established early in the disk evolution. It is also consistent with the reported radial gradients in the mean grain size, crystallinity, and crystal composition. In addition, this model yields the properties of the grains that remain embedded in the outflows from protoplanetary disks and naturally explains the inferred persistence of small grains in the surface layers of these disks.

We present a new and independent determination of the local value of the Hubble constant based on a calibration of the tip of the red giant branch (TRGB) applied to Type Ia supernovae (SNe Ia). We find a value of H₀ = 69.8 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s⁻¹ Mpc⁻¹. The TRGB method is both precise and accurate and is parallel to but independent of the Cepheid distance scale. Our value sits midway in the range defined by the current Hubble tension. It agrees at the 1.2σ level with that of the Planck Collaboration et al. estimate and at the 1.7σ level with the Hubble Space Telescope (HST) SHoES measurement of H₀ based on the Cepheid distance scale. The TRGB distances have been measured using deep HST Advanced Camera for Surveys imaging of galaxy halos. The zero-point of the TRGB calibration is set with a distance modulus to the Large Magellanic Cloud of 18.477 ± 0.004 (stat) ± 0.020 (sys) mag, based on measurement of 20 late-type detached eclipsing binary stars, combined with an HST parallax calibration of a 3.6 μm Cepheid Leavitt law based on Spitzer observations. We anchor the TRGB distances to galaxies that extend our measurement into the Hubble flow using the recently completed Carnegie Supernova Project I ( CSP-I ) sample containing about 100 well-observed SNe Ia . There are several advantages of halo TRGB distance measurements relative to Cepheid variables; these include low halo reddening, minimal effects of crowding or blending of the photometry, only a shallow (calibrated) sensitivity to metallicity in the I band, and no need for multiple epochs of observations or concerns of different slopes with period. In addition, the host masses of our TRGB host-galaxy sample are higher, on average, than those of the Cepheid sample, better matching the range of host-galaxy masses in the CSP-I distant sample and reducing potential systematic effects in the SNe Ia measurements.

Planetary-scale collisions are common during the last stages of formation of solid planets, including the solar system terrestrial planets. The problem of growing planets has been divided into studying the gravitational interaction of embryos relevant on million year timescales and treated with N-body codes and the collision between objects with a timescale of hours to days and treated with smoothed-particle hydrodynamics. These are now being coupled with simple parameterized models. We set out to investigate if machine-learning techniques can offer a better solution by predicting the outcome of collisions that can then be used in N-body simulations. We considered three different supervised machine-learning approaches: gradient boosting regression trees, nested models, and Gaussian processes (GPs). We found that the former produced the best results, and that it was slightly surpassed by ensembling different algorithms. With GPs, we found the regions of parameter space that may yield the most information to machine-learning algorithms. Thus, we suggest new smoothed-particle hydrodynamics calculations to focus first on mass ratios ≳0.5.

Pair-instability and pulsational pair-instability supernovae (PPISNe) have not been unambiguously observed so far. They are, however, promising candidates for the progenitors of the heaviest binary black hole (BBH) mergers detected. If these BBHs are the product of binary evolution, then PPISNe could occur in very close binaries. Motivated by this, we discuss the implications of a PPISN happening with a close binary companion and what impact these events have on the formation of merging BBHs through binary evolution. For this, we have computed a set of models of metal-poor (Z_⊙/10) single helium stars using the MESA software instrument. For PPISN progenitors with pre-pulse masses >50 M_⊙ we find that, after a pulse, heat deposited throughout the layers of the star that remain bound causes it to expand to more than 100 R_⊙ for periods of 10²–10⁴ yr depending on the mass of the progenitor. This results in long-lived phases of Roche lobe overflow or even common-envelope events if there is a close binary companion, leading to additional electromagnetic transients associated with PPISN eruptions. If we ignore the effect of these interactions, we find that mass loss from PPISNe reduces the final BH spin by ∼30%, induces eccentricities below the threshold of detectability of the LISA observatory, and can produce a double-peaked distribution of measured chirp masses in BBH mergers observed by ground-based detectors.

Molecules and dust produced by the atmospheres of cool evolved stars contribute to a significant amount of the total material found in the interstellar medium. To understand the mechanism behind the mass loss of these stars, it is of pivotal importance to investigate the structure and dynamics of their atmospheres. Our goal is to verify if the extended molecular and dust layers of the carbon-rich asymptotic giant branch (AGB) star V Oph, and their time variations, can be explained by dust-driven winds triggered by stellar pulsation alone, or if other mechanisms are in play. We model V Oph mid-infrared interferometric VLTI-MIDI data (8–13 μm), at phases 0.18, 0.49, and 0.65, together with literature photometric data, using the latest-generation self-consistent dynamic atmosphere models for carbon-rich stars: DARWIN. We determine the fundamental stellar parameters: T_eff = 2600 K, L_bol = 3585 L_⊙, M = 1.5 M_⊙, C/O = 1.35, $\dot{M}=2.50\times {10}^{-6}$M_⊙ yr⁻¹. We calculate the stellar photospheric radii at the three phases: 479, 494, 448 R_⊙; and the dust radii: 780, 853, 787 R_⊙. The dynamic models can fairly explain the observed N-band visibility and spectra, although there is some discrepancy between the data and the models, which is discussed in the text. We discuss the possible causes of the temporal variations of the outer atmosphere, deriving an estimate of the magnetic field strength, and computing upper limits for the Alfvén waves velocity. In addition, using period–luminosity sequences, and interferometric modeling, we suggest V Oph as a candidate to be reclassified as a semi-regular star.

Though they are the most abundant stars in the Galaxy, M dwarfs form only a small subset of known stars hosting exoplanets with measured radii and masses. In this paper, we analyze the mass–radius (M-R) relationship of planets around M dwarfs using M-R measurements for 24 exoplanets. In particular, we apply both parametric and nonparametric models and compare the two different fitting methods. We also use these methods to compare the results of the M dwarf M-R relationship with that from the Kepler sample. Using the nonparametric method, we find that the predicted masses for the smallest and largest planets around M dwarfs are smaller than similar fits to the Kepler data, but that the distribution of masses for 3 R_⊕ planets does not substantially differ between the two data sets. With future additions to the M dwarf M-R relation from the Transiting Exoplanet Survey Satellite and instruments like the Habitable Zone Planet Finder, we will be able to characterize these differences in more detail. We release a publicly available Python code called MRExo (https://github.com/shbhuk/mrexo) that uses the nonparametric algorithm introduced by Ning et al. to fit the M-R relationship. Such a nonparametric fit does not assume an underlying power-law fit to the measurements and hence can be used to fit an M-R relationship that is less biased than a power law. In addition, MRExo offers a tool to predict mass from radius posteriors, and vice versa.

In the quadrupole approximation of general relativity in the weak-field limit, a time-varying quadrupole moment generates gravitational radiation. Binary orbits are one of the main mechanisms for producing gravitational waves and are the main sources and backgrounds for gravitational-wave detectors across the multiband spectrum. In this paper, we introduce additional contributions to the gravitational radiation from close binaries that arise from time-varying masses along with those produced by orbital motion. We derive phase-dependent formulae for these effects in the quadrupolar limit for binary point masses, which reduce to the formulae that Peters & Mathews derived when the mass of each component is taken to be constant. We show that gravitational radiation from mass variation can be orders of magnitude greater than that of orbital motion.

Multimessenger observations of the neutron star merger GW170817 and its kilonova proved that neutron star mergers can synthesize large quantities of r-process elements. If neutron star mergers in fact dominate all r-process element production, then the distribution of kilonova ejecta compositions should match the distribution of r-process abundance patterns observed in stars. The lanthanide fraction (X_La) is a measurable quantity in both kilonovae and metal-poor stars, but it has not previously been explicitly calculated for stars. Here we compute the lanthanide fraction distribution of metal-poor stars ([Fe/H] < − 2.5) to enable comparison to current and future kilonovae. The full distribution peaks at log X_La ∼ −1.8, but r-process-enhanced stars ([Eu/Fe] > 0.7) have distinctly higher lanthanide fractions: $\mathrm{log}{X}_{\mathrm{La}}\gtrsim -1.5$. We review observations of GW170817 and find general consensus that the total $\mathrm{log}{X}_{\mathrm{La}}=-2.2\pm 0.5$, somewhat lower than the typical metal-poor star and inconsistent with the most highly r-enhanced stars. For neutron star mergers to remain viable as the dominant r-process site, future kilonova observations should be preferentially lanthanide-rich (including a population of ∼10% with $\mathrm{log}{X}_{\mathrm{La}}\gt -1.5$). These high-X_La kilonovae may be fainter and more rapidly evolving than GW170817, posing a challenge for discovery and follow-up observations. Both optical and (mid-)infrared observations will be required to robustly constrain kilonova lanthanide fractions. If such high-X_La kilonovae are not found in the next few years, that likely implies that the stars with the highest r-process enhancements have a different origin for their r-process elements.

We present Chandra ACIS-S X-ray imaging spectroscopy for five dual active galactic nucleus (AGN) candidates. Our targets were drawn from a sample of 1286 [O III]-selected AGN pairs systematically selected from the Sloan Digital Sky Survey Seventh Data Release. Each of the targets contains two nuclei separated by ∼3–9 kpc in projection, both of which are optically classified as Type 2 (obscured) AGNs based on diagnostic ratios of the narrow emission lines. Combined with independent, empirical star formation rate estimates based on the host-galaxy stellar continua, the new Chandra X-ray observations allow us to evaluate the dual-AGN hypothesis for each merging system. We confirm two (SDSS J0907+5203 and SDSS J1544+0446) of the five targets as bona fide dual AGNs. For the other three targets, the existing data are consistent with the dual-AGN scenario, but we cannot rule out the possibility of stellar/shock heating and/or one AGN ionizing both gaseous components in the merger. The average X-ray-to-[O III] luminosity ratio in our targets seems to be systematically smaller than that observed in single AGNs but is higher than that seen in dual AGNs selected from AGNs with double-peaked narrow emission lines. We suggest that the systematically smaller X-ray-to-[O III] luminosity ratio observed in dual AGNs than in single AGNs is due to a high nuclear gas column likely from strong merger-induced inflows. Unlike double-peaked-[O III]-selected dual AGNs, the new sample selected from resolved galaxy pairs are not subject to the orientation bias caused by the double-peak line-of-sight velocity splitting selection, which also contributes to lowering the X-ray-to-[O III] luminosity ratio.

We present the Super Eight galaxies—a set of very luminous, high-redshift (7.1 < z < 8.0) galaxy candidates found in the Brightest of Reionizing Galaxies (BoRG) Survey fields. The original sample includes eight galaxies that are Y-band dropout objects with H-band magnitudes of m_H < 25.5. Four of these objects were originally reported in Calvi et al. Combining new Hubble Space Telescope (HST) WFC3/F814W imaging and Spitzer IRAC data with archival imaging from BoRG and other surveys, we explore the properties of these galaxies. Photometric redshift fitting places six of these galaxies in the redshift range of 7.1 < z < 8.0, resulting in three new high-redshift galaxies and confirming three of the four high-redshift galaxy candidates from Calvi et al. We calculate the half-light radii of the Super Eight galaxies using the HST F160W filter and find that the Super Eight sizes are in line with the typical evolution of size with redshift. The Super Eights have a mean mass of log (M_*/M_⊙) ∼10, which is typical for sources in this luminosity range. Finally, we place our sample on the UV z ∼ 8 luminosity function and find that the Super Eight number density is consistent with other surveys in this magnitude and redshift range.

The old open cluster M67, populated with blue straggler stars (BSSs), is a well-known test bed to study the BSS formation pathways. Here, we report the first direct detection of a white dwarf (WD) companion to a BSS in M67, using far-UV images from the Ultra-Violet Imaging telescope on ASTROSAT. Near-simultaneous observations in three far-UV bands combined with Galaxy Evolution Explorer, International Ultraviolet Explorer, and ground- and space-based photometric data covering a 0.14–11.5 μm range for WOCS1007 were found to require a binary fit to its spectral energy distribution (SED), consisting of a BSS and a hot companion. On the other hand, a single spectral fit was found to be satisfactory for the SEDs of two other BSSs, WOCS1006 and WOCS2011, with the latter showing a deficient far-UV flux. The hot companion of WOCS1007 is found to have a ${T}_{\mathrm{eff}}$ ∼ 13,250–13,750 K and a radius of 0.09 ± 0.01 ${R}_{\odot }$. A comparison with WD models suggests it to be a low-mass WD (∼$0.18{M}_{\odot }$), in agreement with the kinematic mass from the literature. As a low-mass WD (<$0.4{M}_{\odot }$) necessitates formation through mass transfer in close binaries, WOCS1007 with a known period of 4.2 days along with its fast rotation, is likely to be formed by a case A or case B binary evolution.

Isoviolanthrene (C₃₄H₁₈), a polycyclic aromatic hydrocarbon (PAH) molecule, was studied via matrix isolation in argon and water at 20 K. Infrared spectroscopy was performed in situ where samples were irradiated using ultraviolet light. Experimental spectra were compared to theoretical spectra for vibrational band assignment, determination of the corresponding A-values, and photoproduct identification. Isoviolanthrene was also deposited as a thin film and irradiated with different energy sources: ultraviolet photons (10.2 eV), soft electrons (1.5 keV), protons (1.5 MeV), and He⁺ particles (1.5 MeV), to understand the effects of different energy sources on a PAH. Anions and cations of isoviolanthrene were produced as a result of UV photolysis in an argon matrix. Hydrogen- and oxygen-rich aromatic photoproducts were produced by ultraviolet photons when isoviolanthrene was isolated in a water matrix. The irradiated PAH thin films results were dependent on the energy source. Irradiation with ultraviolet photons yielded a broad underlying feature centered at 9.6 μm, while bombardment with soft electrons gave a broad feature centered at 7.7 μm. In the case of proton bombardment, no broad feature was detected, in contrast with He⁺ bombardment that destroyed most of the isoviolanthrene and produced broad features in the C-Hoop and C–H stretching regions. A comparison of astronomical IR emission observations with our experimental results in the mid-infrared range has revealed a similarity between the observed plateaus and the broad features produced by our experiments.

We have investigated the formation and kinematics of submillimeter (submm) continuum cores in the Orion A molecular cloud. A comparison between submm continuum and near-infrared extinction shows a continuum core detection threshold of A_V ∼ 5–10 mag. The threshold is similar to the star formation extinction threshold of A_V ∼ 7 mag proposed by recent work, suggesting a universal star formation extinction threshold among clouds within 500 pc to the Sun. A comparison between the Orion A cloud and a massive infrared dark cloud G28.37+0.07 indicates that Orion A produces more dense gas within the extinction range 15 mag ≲ A_V ≲ 60 mag. Using data from the CARMA-NRO Orion Survey, we find that dense cores in the integral-shaped filament (ISF) show subsonic core-to-envelope velocity dispersion that is significantly less than the local envelope line dispersion, similar to what has been found in nearby clouds. Dynamical analysis indicates that the cores are bound to the ISF. An oscillatory core-to-envelope motion is detected along the ISF. Its origin is to be further explored.

Galaxies covering several orders of magnitude in stellar mass and a variety of Hubble types have been shown to follow the radial acceleration relation (RAR), a relationship between ${g}_{\mathrm{obs}}$, the observed circular acceleration of the galaxy, and ${g}_{\mathrm{bar}}$, the acceleration due to the total baryonic mass of the galaxy. For accelerations above ${10}^{10}\,{\rm{m}}\,{{\rm{s}}}^{-2}$, ${g}_{\mathrm{obs}}$ traces ${g}_{\mathrm{bar}}$, asymptoting to the 1:1 line. Below this scale, there is a break in the relation such that ${g}_{\mathrm{obs}}\sim {g}_{\mathrm{bar}}^{1/2}$. We show that the RAR slope, scatter, and the acceleration scale are all natural consequences of the well-known baryonic Tully–Fisher relation (BTFR). We further demonstrate that galaxies with a variety of baryonic and dark matter (DM) profiles and a wide range of dark halo and galaxy properties (well beyond those expected in Cold Dark Matter (CDM) theory) lie on the RAR if we simply require that their rotation curves satisfy the BTFR. We explore conditions needed to break this degeneracy: subkiloparsec resolved rotation curves inside of cored DM-dominated profiles and/or outside $\gg 100\,\mathrm{kpc}$ could lie on BTFR but deviate in the RAR, providing new constraints on DM.

The Cassini mission revealed gas plumes associated with surface features called "tiger stripes" at the south pole of Saturn's moon Enceladus. The composition of plume particles and local cryovolcanism suggested as a possible cause for the activity are typically considered in the context of hydrothermal circulation in the rocky core within a differentiated core–ocean–ice crust structure. We model the internal evolution and differentiation of Enceladus heated by radioactive nuclides and tidal dissipation. Calculating the core formation, we investigate its compaction by modeling the evolution of porosity, thereby varying the rock rheology based on different assumptions on the composition, such as grain size, creep activation energy, degree of hydration, and oxygen fugacity. We present final structures with a core radius of 185–205 km, a porous core layer of 4–70 km, an ocean of ≈10–27 km, and an ice crust layer of ≈30–40 km, that are largely consistent with the current estimates for Enceladus. By fitting the model results to these observations, we determine an accretion time of 1.3–2.3 Ma after calcium–aluminum-rich inclusions for Enceladus. Our models produce a porous outer core for wet and dry olivine rock rheologies supporting the hypothesis of hydrothermal circulation of oceanic water in the core. No porosity is retained for an antigorite rheology, implying that the core of Enceladus is not dominated by this mineral.

Using the cross-matched data of Gaia DR2 and the 2MASS Point Source Catalog, we investigated the surface density distribution of stars aged ∼1 Gyr in the thin disk in the range of 90° ≤ l ≤ 270°. We selected 4654 stars above the turnoff corresponding to the age ∼1 Gyr, that fall within a small box region in the color–magnitude diagram, (J − K_s)₀ versus M(K_s), for which the distance and reddening are corrected. The selected sample shows an arm-like overdensity at 90° ≤ l ≤ 190°. This overdensity is located close to the Local Arm traced by high-mass star-forming regions (HMSFRs), but its pitch angle is slightly larger than that of the HMSFR-defined arm. Although the significance of the overdensity we report is marginal, its structure poses questions concerning both of the competing scenarios of spiral arms, the density-wave theory, and the dynamic spiral arm model. The offset between the arms traced by stars and HMSFRs, i.e., gas, is difficult to explain using the dynamic arm scenario. On the other hand, the pitch angle of the stellar Local Arm, if confirmed, is larger than that of the Perseus arm, and is difficult to explain using the classical density-wave scenario. The dynamic arm scenario can explain the pitch angle of the stellar Local Arm, if the Local Arm is in a growing up phase, while the Perseus arm is in a disrupting phase. Our result provide a new and complex picture of the Galactic spiral arms, and encourages further studies.

We present a high-resolution (∼012, ∼16 au, mean sensitivity of 50 μJy beam⁻¹ at 225 GHz) snapshot survey of 32 protoplanetary disks around young stars with spectral type earlier than M3 in the Taurus star-forming region using the Atacama Large Millimeter Array. This sample includes most mid-infrared excess members that were not previously imaged at high spatial resolution, excluding close binaries and objects with high extinction, thereby providing a more representative look at disk properties at 1–2 Myr. Our 1.3 mm continuum maps reveal 12 disks with prominent dust gaps and rings, 2 of which are around primary stars in wide binaries, and 20 disks with no resolved features at the observed resolution (hereafter smooth disks), 8 of which are around the primary star in wide binaries. The smooth disks were classified based on their lack of resolved substructures, but their most prominent property is that they are all compact with small effective emission radii (R_eff,95% ≲ 50 au). In contrast, all disks with R_eff,95% of at least 55 au in our sample show detectable substructures. Nevertheless, their inner emission cores (inside the resolved gaps) have similar peak brightness, power-law profiles, and transition radii to the compact smooth disks, so the primary difference between these two categories is the lack of outer substructures in the latter. These compact disks may lose their outer disk through fast radial drift without dust trapping, or they might be born with small sizes. The compact dust disks, as well as the inner disk cores of extended ring disks, that look smooth at the current resolution will likely show small-scale or low-contrast substructures at higher resolution. The correlation between disk size and disk luminosity correlation demonstrates that some of the compact disks are optically thick at millimeter wavelengths.

It is widely accepted in the MHD turbulence community that the nonlinear cascade of wave energy requires counterpropagating Alfvénic wave packets, along some mean magnetic field. This fact is an obvious outcome of the MHD equations under the assumptions of incompressibility and homogeneity. Despite attempts to relax these assumptions in the context of MHD turbulence, the central idea of turbulence generation persists. However, once the assumptions of incompressiblity and homogeneity break down, the generally accepted picture of turbulent cascade generation is not universal. In this paper, we show that perpendicular inhomogeneities (across the mean magnetic field) lead to propagating wave solutions that are necessarily described by co-propagating Elsässer fields, already in the incompressible case. One simple example of these wave solutions is the surface Alfvén wave on a planar discontinuity across the magnetic field. We show through numerical simulations how the nonlinear self-deformation of these unidirectionally propagating waves leads to a cascade of wave energy across the magnetic field. The existence of this type of unidirectional cascade might have an additional strong effect on the turbulent dissipation rate of dominantly outward-propagating Alfvénic waves in structured plasma, as in the solar corona and solar wind.

The release of density structures at the tip of the coronal helmet streamers, likely as a consequence of magnetic reconnection, contributes to the mass flux of the slow solar wind (SSW). In situ measurements in the vicinity of the heliospheric plasma sheet of the magnetic field, protons, and suprathermal electrons reveal details of the processes at play during the formation of density structures near the Sun. In a previous article, we exploited remote-sensing observations to derive a 3D picture of the dynamic evolution of a streamer. We found evidence of the recurrent and continual release of dense blobs from the tip of the streamers. In the present paper, we interpret in situ measurements of the SSW during solar maximum. Through both case and statistical analysis, we show that in situ signatures (magnetic field magnitude, smoothness and rotation, proton density, and suprathermal electrons, in the first place) are consistent with the helmet streamers producing, in alternation, high-density regions (mostly disconnected) separated by magnetic flux ropes (mostly connected to the Sun). This sequence of emission of dense blobs and flux ropes also seems repeated at smaller scales inside each of the high-density regions. These properties are further confirmed with in situ measurements much closer to the Sun using Helios observations. We conclude on a model for the formation of dense blobs and flux ropes that explains both the in situ measurements and the remote-sensing observations presented in our previous studies.

The delay time distribution of Type Ia supernovae (SNe Ia; the time-dependent rate of SNe resulting from a burst of star formation) has been measured using different techniques and in different environments. Here we study in detail the distribution for field galaxies, using the SDSS DR7 Stripe 82 SN sample. We improve a technique we introduced earlier, which is based on galaxy color and luminosity and is insensitive to details of the star formation history, to include the normalization. Assuming a power-law dependence of the SN rate with time, DTD(t) = A(t/1 Gyr)^s, we find a power-law index $s=-{1.34}_{-0.17}^{+0.19}$ and a normalization $\mathrm{log}\ A=-{12.15}_{-0.13}^{+0.10}\,\mathrm{dex}({M}_{\odot }^{-1}\,{\mathrm{yr}}^{-1})$, corresponding to a number of SNe Ia integrated over a Hubble time of ${k}_{\mathrm{Ia}}={0.004}_{-0.001}^{+0.002}\,{M}_{\odot }^{-1}$. We also implement a method used by Maoz and collaborators, which is based on star formation history reconstruction, and find that this gives a consistent result for the slope but a lower, marginally inconsistent normalization. With our normalization, the distribution for field galaxies is made consistent with that derived for cluster galaxies. Comparing the inferred distribution with predictions from different evolutionary scenarios for SNe Ia, we find that our results are intermediate between the various predictions and do not yet constrain the evolutionary path leading to SNe Ia.

Fermi-Gamma-ray Burst Monitor observed a 1 s long gamma-ray signal (GW150914-GBM) starting 0.4 s after the first gravitational-wave detection from the binary black hole (BH) merger GW150914. GW150914-GBM is consistent with a short gamma-ray burst origin; however, no unambiguous claims can be made as to the physical association of the two signals due to a combination of low gamma-ray flux and the unfavorable location of Fermi-GBM. Here we answer the following question: if GW150914 and GW150914-GBM were associated, how many LIGO-Virgo binary BH mergers would Fermi-GBM have to follow up to detect a second source? To answer this question, we perform simulated observations of binary BH mergers with LIGO-Virgo and adopt different scenarios for gamma-ray emission from the literature. We calculate the ratio of simulated binary BH mergers detected by LIGO-Virgo to the number of gamma-ray counterpart detections by Fermi-GBM, the BBH-to-GRB ratio. A large majority of the models considered here predict a BBH-to-GRB ratio in the range of 5–20, but for optimistic cases it can be as low as 2, while for pessimistic assumptions it can be as high as 700. Hence, we expect that the third observing run, with its high rate of binary BH detections and assuming the absence of a joint detection, will provide strong constraints on the presented models.

Corotating interaction regions (CIRs) are responsible for short-term recurrent cosmic-ray modulation, prominent near solar minima. Using the OMNI data sets for two periods of low solar activity near the beginning and end of solar cycle 24, superposed epoch analysis was performed on the solar wind plasma features for 53 and 43 events during periods 2007–2008 and 2017–2018, respectively. Turbulent properties of the solar wind were studied using the variance method for each CIR. Power spectra have been constructed for overlapped subintervals in the vicinity of stream interfaces (SIs). Using measured correlation lengths and turbulent energies, parallel and perpendicular diffusion mean free paths for cosmic-ray ions have been inferred based on two distinct theoretical formulations. For the two periods with opposite solar polarities, our results show that unlike solar wind speed, magnetic field strength, flow pressure, and proton density are relatively higher during the latest period. Increased turbulent energy and reduced parallel transport coefficients of energetic particles at the SIs are observed. The diffusion coefficients follow the same trends during both periods. The perpendicular diffusion starts increasing nearly a day before SIs and is higher in the fast wind. Superposed epoch analysis is performed on the >120 MeV proton count rate obtained from the CRIS instrument on board the ACE spacecraft for the same events. The recorded proton rates have peaks half a day before a SI and reach their minimum more than a day after a SI and have a high anticorrelation with the perpendicular diffusion coefficient.

We perform simulations to study the effects of active galactic nuclei (AGNs) radiation and wind feedback on the properties of slowly rotating accretion flow at the parsec scale. We find that when only radiative feedback is considered, outflows can be produced by the radiation pressure due to Thomson scattering. The mass flux of outflow is comparable to that of inflow. Although strong outflow is present, the luminosity of the AGN can be easily super-Eddington. When wind feedback is also taken into account, the mass flux of outflow does not change much. Consequently, the luminosity of the central AGN can still be super-Eddington. However, observations show that the luminosity of most AGNs is sub-Eddington. Some other mechanisms are needed to reduce the AGNs' luminosity. Although the mass outflow rate is not changed much by wind feedback, other properties of outflow (the density, temperature, velocity, and kinetic power) can be significantly changed by wind feedback. In the presence of wind feedback, the density of outflow becomes significantly lower, the temperature of outflow becomes significantly higher, the velocity of outflow is increased by one order of magnitude, and the kinetic power of outflow is increased by a factor of 40–100.

We have systematically investigated a series of polycyclic aromatic hydrocarbons (PAHs) with armchair edges that maximize the aromaticity, denoted as Clar PAHs, using density functional theory. Their structures fall into three major categories: branched, intermediate, and armchair. Branched PAHs contain up to 60 carbons, they are eroded and the least stable, and their spectra are the most complex. Armchair PAHs are the most stable and their spectra differ from the nominal PAH spectra by lacking a 11.2 μm band and having their 7.8 and 8.2 μm bands coalesce as their size increases. Only intermediate and armchair PAHs have 12.7/13.5 μm PAH band intensity ratios that are consistent with observations. The fitting results show that Clar PAH spectra are more consistent with class B than class A sources, with only a few small Clar PAHs contributing to the fit of the class A source IRAS 23133+6050 and large Clar PAHs contributing to the fit of the class B source IRAS 17347−3139, and NGC 7027. Overall, our study suggests that large Clar PAHs are potential emitters in class B sources.

The interaction between emerging and pre-existing magnetic fields in the solar atmosphere can trigger several dynamic phenomena, such as eruptions and jets. A key element during this interaction is the formation of large-scale current sheets, and eventually their fragmentation that leads to the creation of a strongly turbulent environment. In this paper, we study the kinetic aspects of the interaction (reconnection) between emerging and ambient magnetic fields. We show that the statistical properties of the spontaneously fragmented and fractal electric fields are responsible for the efficient heating and acceleration of charged particles, which form a power-law tail at high energies on sub-second timescales. A fraction of the energized particles escapes from the acceleration volume, with a super-hot component with a temperature close to 150 MK, and with a power-law high-energy tail with an index between −2 and −3. We estimate the transport coefficients in energy space from the dynamics of the charged particles inside the fragmented and fractal electric fields, and the solution of a fractional transport equation, as appropriate for a strongly turbulent plasma, agrees with the test-particle simulations. We also show that the acceleration mechanism is not related to Fermi acceleration, and the Fokker–Planck equation is inconsistent and not adequate as a transport model. Finally, we address the problem of correlations between spatial transport and transport in energy space. Our results confirm the observations reported for high-energy particles (hard X-rays, type III bursts, and solar energetic particles) during the emission of solar jets.

Foreground power dominates the measurements of interferometers that seek a statistical detection of highly-redshifted H i emission from the Epoch of Reionization (EoR). The chromaticity of the instrument creates a boundary in the Fourier transform of frequency (proportional to k_∥) between spectrally smooth emission, characteristic of the strong synchrotron foreground (the "wedge"), and the spectrally structured emission from H i in the EoR (the "EoR window"). Faraday rotation can inject spectral structure into otherwise smooth polarized foreground emission, which through instrument effects or miscalibration could possibly pollute the EoR window. For instruments pursuing a "foreground avoidance" strategy of simply measuring in the EoR window, and not attempting to model and remove foregrounds, as is the plan for the first stage of the Hydrogen Epoch of Reionization Array (HERA), characterizing the intrinsic instrument polarization response is particularly important. Using data from the HERA 19-element commissioning array, we investigate the polarization response of this new instrument in the power-spectrum domain. We perform a simple image-based calibration based on the unpolarized diffuse emission of the Global Sky Model, and show that it achieves qualitative redundancy between the nominally redundant baselines of the array and reasonable amplitude accuracy. We construct power spectra of all fully polarized coherencies in all pseudo-Stokes parameters, and discuss the achieved isolation of foreground power due to the intrinsic spectral smoothness of the foregrounds, the instrument chromaticity, and the calibration. We compare to simulations based on an unpolarized diffuse sky model and detailed electromagnetic simulations of the dish and feed, confirming that in Stokes I, the calibration does not add significant spectral structure beyond that expected from the interferometer array configuration and the modeled primary beam response. Furthermore, this calibration is stable over the 8 days of observations considered. Excess power is seen in the power spectra of the linear polarization Stokes parameters, which is not easily attributable to leakage via the primary beam, and results from some combination of residual calibration errors and actual polarized emission. Stokes V is found to be highly discrepant from the expectation of zero power, strongly pointing to the need for more accurate polarized calibration.

The system A1758 is made up of two galaxy clusters, a more massive, northern cluster and a southern cluster. Both parts are undergoing major merger events at different stages. Although the mass of the merger constituents provides enough energy to produce visible shock fronts in the X-ray, none have been found to date. We present detailed temperature and abundance maps based on Chandra ACIS data and identify several candidates for shocks and cold fronts from a smoothed gradient map of the surface brightness. One candidate can be confirmed as the missing shock front in the northern cluster through X-ray spectroscopy. Nonthermal radio emission observed with the GMRT confirms the presence of radio halos in the northern and southern clusters and shows evidence for a relic in the periphery of the southern cluster. We do not find evidence for shocked gas between A1758 N and A1758 S.

Interstellar neutral gas atoms penetrate the heliopause and reach 1 au, where they are detected by Interstellar Boundary Explorer (IBEX). The flow of neutral interstellar helium through the perturbed interstellar plasma in the outer heliosheath (OHS) results in the creation of a secondary population of interstellar He atoms, the so-called Warm Breeze, due to charge exchange with perturbed ions. The secondary population brings the imprint of the OHS conditions to the IBEX-Lo instrument. Based on a global simulation of the heliosphere with measurement-based parameters and detailed kinetic simulation of the filtration of He in the OHS, we find the number density of the interstellar He⁺ population to be (8.98 ± 0.12) × 10⁻³ cm⁻³. With this, we obtain the absolute density of interstellar H⁺ as 5.4 × 10⁻² cm⁻³ and that of electrons as 6.3 × 10⁻² cm⁻³, with ionization degrees of 0.26 for H and 0.37 for He. The results agree with estimates of the parameters of the Very Local Interstellar Matter obtained from fitting the observed spectra of diffuse interstellar EUV and the soft X-ray background.

We present an enhanced version of the multiwavelength spectral modeling code MAGPHYS that allows the estimation of galaxy photometric redshift and physical properties (e.g., stellar mass, star formation rate, dust attenuation) simultaneously, together with robust characterization of their uncertainties. The self-consistent modeling over ultraviolet to radio wavelengths in MAGPHYS+photo-z is unique compared to standard photometric redshift codes. The broader wavelength consideration is particularly useful for breaking certain degeneracies in color versus redshift for dusty galaxies with limited observer-frame ultraviolet and optical data (or upper limits). We demonstrate the success of the code in estimating redshifts and physical properties for over 4000 infrared-detected galaxies at 0.4 < z < 6.0 in the COSMOS field with robust spectroscopic redshifts. We achieve high photo-z precision (${\sigma }_{{\rm{\Delta }}z/(1+{z}_{\mathrm{spec}})}\lesssim 0.04$), high accuracy (i.e., minimal offset biases; median(Δz/(1 + z_spec)) ≲ 0.02), and low catastrophic failure rates (η ≃ 4%) over all redshifts. Interestingly, we find that a weak 2175 Å absorption feature in the attenuation curve models is required to remove a subtle systematic z_phot offset (${z}_{\mathrm{phot}}\mbox{--}{z}_{\mathrm{spec}}\simeq -0.03$) that occurs when this feature is not included. As expected, the accuracy of derived physical properties in MAGPHYS+photo-z decreases strongly as redshift uncertainty increases. The all-in-one treatment of uncertainties afforded with this code is beneficial for accurately interpreting physical properties of galaxies in large photometric data sets. Finally, we emphasize that MAGPHYS+photo-z is not intended to replace existing photo-z codes, but rather offers flexibility to robustly interpret physical properties when spectroscopic redshifts are unavailable. The MAGPHYS+photo-z code is publicly available online.

We present the first measurement of cross-correlation between the lensing potential, reconstructed from cosmic microwave background (CMB) polarization data, and the cosmic shear field from galaxy shapes. This measurement is made using data from the Polarbear CMB experiment and the Subaru Hyper Suprime-Cam (HSC) survey. By analyzing an 11 deg² overlapping region, we reject the null hypothesis at 3.5σ and constrain the amplitude of the cross-spectrum to ${\widehat{A}}_{\mathrm{lens}}=1.70\pm 0.48$, where ${\widehat{A}}_{\mathrm{lens}}$ is the amplitude normalized with respect to the Planck 2018 prediction, based on the flat Λ cold dark matter cosmology. The first measurement of this cross-spectrum without relying on CMB temperature measurements is possible owing to the deep Polarbear map with a noise level of ∼6 μK arcmin, as well as the deep HSC data with a high galaxy number density of ${n}_{g}=23\,{\mathrm{arcmin}}^{-2}$. We present a detailed study of the systematics budget to show that residual systematics in our results are negligibly small, which demonstrates the future potential of this cross-correlation technique.

We present ^1DMESA2HYDRO^3D, an open-source, Python-based software tool that provides an accessible means of generating physically motivated initial conditions (ICs) for hydrodynamical simulations from 1D stellar structure models. We test ^1DMESA2HYDRO^3D on five stellar models generated with the MESA stellar evolution code and verify its capacity as an IC generator with the Phantom smoothed particle hydrodynamics code. Consistency between the input density profiles, the ^1DMESA2HYDRO^3D-rendered particle distributions, and the state of the distributions after evolution over 10 dynamical timescales is found for model stars ranging in structure and density from a radially extended supergiant to a white dwarf.

We have obtained Hubble Space Telescope STIS and NICMOS and Gemini/GPI scattered-light images of the HD 191089 debris disk. We identify two spatial components: a ring resembling the Kuiper Belt in radial extent (FWHM ∼ 25 au, centered at ∼46 au) and a halo extending to ∼640 au. We find that the halo is significantly bluer than the ring, consistent with the scenario that the ring serves as the "birth ring" for the smaller dust in the halo. We measure the scattering phase functions in the 30°–150° scattering-angle range and find that the halo dust is more forward- and backward-scattering than the ring dust. We measure a surface density power-law index of −0.68 ± 0.04 for the halo, which indicates the slowdown of the radial outward motion of the dust. Using radiative transfer modeling, we attempt to simultaneously reproduce the (visible) total and (near-infrared) polarized intensity images of the birth ring. Our modeling leads to mutually inconsistent results, indicating that more complex models, such as the inclusion of more realistic aggregate particles, are needed.

We investigate the stellar and dust properties of massive (log M_*/M_⊙ ≥ 10.5) and dusty (A_V ≥ 1) galaxies at 1 ≤ z ≤ 4 by modeling their spectral energy distributions (SEDs) obtained from the combination of UltraVISTA DR3 photometry and Herschel PACS-SPIRE data using MAGPHYS. Although the rest-frame U–V versus V–J (UVJ) diagram traces the star formation rates (SFRs) and dust obscuration (A_V) well out to z ∼ 3, ∼15%–20% of the sample surprisingly resides in the quiescent region of the UVJ diagram, while ∼50% at 3 < z < 4 falls in the unobscured star-forming region. The median SED of massive dusty galaxies exhibits weaker MIR and UV emission, and redder UV slopes with increasing cosmic time. The IR emission for our sample has a significant contribution (>20%) from dust heated by evolved stellar populations rather than star formation, demonstrating the need for panchromatic SED modeling. The local relation between dust mass and SFR is followed only by a subsample with cooler dust temperatures, while warmer objects have reduced dust masses at a given SFR. Most star-forming galaxies in our sample do not follow local IRX–β relations, though IRX does strongly correlate with A_V. Our sample follows local relations, albeit with large scatter, between ISM diagnostics and sSFR. We show that FIR-detected sources represent the extreme of a continuous population of dusty galaxies rather than a fundamentally different population. Finally, using commonly adopted relations to derive SFRs from the combination of the rest-frame UV and the observed 24 μm is found to overestimate the SFR by a factor of 3–5 for the galaxies in our sample.

The interactions among objects in a mean motion resonance are important for the orbital evolution of satellites and rings, especially Saturn's ring arcs and associated moons. In this work, we examine interactions among massive bodies in the same corotation eccentricity resonance site that affect the orbital evolution of those bodies using numerical simulations. During these simulations, the bodies exchange angular momentum and energy during close encounters, altering their orbits. This energy exchange, however, does not mean that one body necessarily moves closer to exact corotation when the other moves away from it. Indeed, if one object moves toward one of these sites, the other object is equally likely to move toward or away from it. This happens because the timescale of these close encounters is short compared to the synodic period between these particles and the secondary mass (i.e., the timescale where corotation sites can be treated as potential maxima). Because the timescale of a gravitational encounter is comparable to the timescale of a collision, we could expect energy to be exchanged in a similar way for collisional interactions. In that case, these findings could be relevant for denser systems like the arcs in Neptune's Adams ring and how they can be maintained in the face of frequent inelastic collisions.

We propose a density-dependent function for the attractive interaction in the original van der Waals model to correctly describe the flow constraint at the high-density regime of the symmetric nuclear matter. After a generalization to asymmetric nuclear matter, it was also possible to study the stellar matter regime from this new model. The mass–radius relation for neutron stars under β-equilibrium is found to agree with recent X-ray observations. The neutron-star masses supported against gravity, obtained from some parameterizations of the model, are in the range of (1.97–2.07)M_⊙, compatible with observational data from the PSR J0348+0432 pulsar. Furthermore, we verify the reliability of the model in predicting tidal deformabilities of the binary system related to the GW170817 neutron-star merger event and find a full agreement with the new bounds obtained by the LIGO/Virgo collaboration.

The optical and ultraviolet broadband photometric and spectroscopic observations of the Type II supernova (SN) 2016gfy are presented. The V-band light curve (LC) shows a distinct plateau phase with a slope of s₂ ∼ 0.12 mag (100 day)⁻¹ and a duration of 90 ± 5 days. Detailed analysis of SN 2016gfy provided a mean ⁵⁶Ni mass of 0.033 ± 0.003 M_⊙, a progenitor radius of ∼350–700 R_⊙, a progenitor mass of ∼12–15 M_⊙, and an explosion energy of (0.9–1.4) × 10⁵¹ erg s⁻¹. The P-Cygni profile of Hα in the early-phase spectra (∼11–21 days) shows a boxy emission. Assuming that this profile arises from the interaction of the SN ejecta with the pre-existing circumstellar material (CSM), it is inferred that the progenitor underwent a recent episode (30–80 yr prior to the explosion) of enhanced mass loss. Numerical modeling suggests that the early LC peak is reproduced better with an existing CSM of 0.15 M_⊙ spread out to ∼70 au. A late-plateau bump is seen in the VRI LCs during ∼50–95 days. This bump is explained as a result of the CSM interaction and/or partial mixing of radioactive ⁵⁶Ni in the SN ejecta. Using strong-line diagnostics, a subsolar oxygen abundance is estimated for the supernova H ii region (12 + log(O/H) = 8.50 ± 0.11), indicating an average metallicity for the host of an SN II. A star formation rate of ∼8.5 M_⊙ yr⁻¹ is estimated for NGC 2276 using the archival GALEX FUV data.

Golovich et al. present an optical imaging and spectroscopic survey of 29 radio relic merging galaxy clusters. In this paper, we study this survey to identify substructure and quantify the dynamics of the mergers. Using a combined photometric and spectroscopic approach, we identify the minimum number of substructures in each system to describe the galaxy populations and estimate the line-of-sight velocity difference between likely merging subclusters. We find that the line-of-sight velocity components of the mergers are typically small compared with the maximum 3D relative velocity (usually <1000 km s⁻¹ and often consistent with zero). We also compare our systems to n-body simulation analogs and estimate the viewing angle of the clean mergers in our ensemble. We find that the median system's separation vector lies within 40° (17°) at a 90% (50%) confidence level. This suggests that the merger axes of these systems are generally in or near the plane of the sky, matching findings in magnetohydrodynamical simulations. In 28 of the 29 systems we identify substructures in the galaxy population aligned with the radio relic(s) and presumed associated merger-induced shock. From this ensemble, we identify eight systems to include in a "gold" sample that is prime for further observation, modeling, and simulation study. Additional papers will present weak-lensing mass maps and dynamical modeling for each merging system, ultimately leading to new insight into a wide range of astrophysical phenomena at some of the largest scales in the universe.

We report our observations of HSC16aayt (SN 2016jiu), which was discovered by the Subaru/Hyper Suprime-Cam (HSC) transient survey conducted as part of the Subaru Strategic Program. It shows very slow photometric evolution and its rise time is more than 100 days. The optical magnitude change in 400 days remains within 0.6 mag. Spectra of HSC16aayt show a strong narrow emission line and we classify it as a Type IIn supernova. The redshift of HSC16aayt is 0.6814 ± 0.0002 from the spectra. Its host galaxy center is at 5 kpc from the supernova location and HSC16aayt might be another example of isolated Type IIn supernovae, although the possible existence of underlying star-forming activity of the host galaxy at the supernova location is not excluded.

We investigate the thermal equation of state, bulk modulus, thermal expansion coefficient, and heat capacity of MH-III (CH₄ filled-ice Ih), needed for the study of CH₄ transport and outgassing for the case of Titan and super-Titans. We employ density functional theory and ab initio molecular dynamics simulations in the generalized-gradient approximation with a van der Waals functional. We examine the temperature range 300–500 K and pressures between 2 and 7 GPa. We find that in this P-T range MH-III is less dense than liquid water. There is uncertainty in the normalized moment of inertia (MOI) of Titan; it is estimated to be in the range of 0.33–0.34. If Titan's MOI is 0.34, MH-III is not stable at present in Titan's interior, yielding an easier path for the outgassing of CH₄. However, for an MOI of 0.33, MH-III is thermodynamically stable at the bottom of an ice-rock internal layer capable of storing CH₄. For rock mass fractions $\lessapprox 0.2$ upwelling melt is likely hot enough to dissociate MH-III along its path. For super-Titans considering a mixture of MH-III and ice VII, melt is always positively buoyant if the H₂O:CH₄ mole fraction is >5.5. Our thermal evolution model shows that MH-III may be present today in Titan's core, confined to a thin (≈10 km) outer shell. We find that the heat capacity of MH-III is higher than measured values for pure water ice, larger than heat capacity often adopted for ice-rock mixtures with implications for internal heating.

We study the structure and dynamics of extreme flaring events on young stellar objects (YSOs) observed in hard X-rays by the Nuclear Spectroscopic Telescope Array (NuSTAR). During 2015 and 2016, NuSTAR made three observations of the star-forming region ρ Ophiuchi, each with an exposure ∼50 ks. NuSTAR offers unprecedented sensitivity above ∼7 keV, making this data set the first of its kind. Through improved coverage of hard X-rays, it is finally possible to directly measure the high-energy thermal continuum for hot plasmas and to sensitively search for evidence of nonthermal emission from YSO flares. During these observations, multiple flares were observed, and spectral and timing analyses were performed on three of the brightest flares. By fitting an optically thin thermal plasma model to each of these events, we found flare plasma heated to high temperatures (∼40−80 MK) and determined that these events are ∼1000 times brighter than the brightest flares observed on the Sun. Two of the studied flares showed excess emission at 6.4 keV, and this excess may be attributable to iron fluorescence in the circumstellar disk. No clear evidence for a nonthermal component was observed, but upper limits on nonthermal emission allow for enough nonthermal energy to account for the estimated thermal energy in the flare on protostar IRS 43, which is consistent with the standard model for solar and stellar flares.