Table of contents

We perform Jeans anisotropic modeling (JAM) on elliptical and spiral galaxies from the MaNGA DR13 sample. By comparing the stellar mass-to-light ratios estimated from stellar population synthesis and from JAM, we find a systematic variation of the initial mass function (IMF) similar to that in the earlier ${\mathrm{ATLAS}}^{3{\rm{D}}}$ results. Early-type galaxies (elliptical and lenticular) with lower velocity dispersions within one effective radius are consistent with a Chabrier-like IMF, while galaxies with higher velocity dispersions are consistent with a more bottom-heavy IMF such as the Salpeter IMF. Spiral galaxies have similar systematic IMF variations, but with slightly different slopes and larger scatters, due to the uncertainties caused by the higher gas fractions and extinctions for these galaxies. Furthermore, we examine the effects of stellar mass-to-light ratio gradients on our JAM modeling, and we find that the trends become stronger after considering the gradients.

Linear and circular polarizations of gamma-ray bursts (GRBs) have been detected recently. We adopt a simplified model to investigate GRB polarization characteristics in this paper. A compressed two-dimensional turbulent slab containing stochastic magnetic fields is considered, and jitter radiation can produce the linear polarization under this special magnetic field topology. Turbulent Faraday rotation measure (RM) of this slab makes strong wavelength-dependent depolarization. The jitter photons can also scatter with those magnetic clumps inside the turbulent slab, and a nonzero variance of the Stokes parameter V can be generated. Furthermore, the linearly and circularly polarized photons in the optical and radio bands may suffer heavy absorptions from the slab. Thus we consider the polarized jitter radiation transfer processes. Finally, we compare our model results with the optical detections of GRB 091018, GRB 121024A, and GRB 131030A. We suggest simultaneous observations of GRB multi-wavelength polarization in the future.

We perform the first reflection study of the soft X-ray transient and Type 1 burst source XTE J1709-267 using NuSTAR observations during its 2016 June outburst. There was an increase in flux near the end of the observations, which corresponds to an increase from ∼0.04 L_Edd to ∼0.06 L_Edd assuming a distance of 8.5 kpc. We have separately examined spectra from the low- and high-flux intervals, which are soft and show evidence of a broad Fe K line. Fits to these intervals with relativistic disk reflection models have revealed an inner-disk radius of ${13.8}_{-1.8}^{+3.0}\ {R}_{g}$ (where ${R}_{g}={GM}/{c}^{2}$) for the low-flux spectrum and ${23.4}_{-5.4}^{+15.6}\,{R}_{g}$ for the high-flux spectrum at the 90% confidence level. The disk is likely truncated by a boundary layer surrounding the neutron star (NS) or the magnetosphere. Based on the measured luminosity and the accretion efficiency for a disk around an NS, we estimate that the theoretically expected size for the boundary layer would be $\sim 0.9\mbox{--}1.1\,{R}_{g}$ from the NS's surface, which can be increased by spin or viscosity effects. Another plausible scenario is that the disk could be truncated by the magnetosphere. We place a conservative upper limit on the strength of the magnetic field at the poles (assuming ${a}_{* }=0$ and ${M}_{\mathrm{NS}}=1.4{M}_{\odot }$) of $B\leqslant 0.75-3.70\times {10}^{9}$ G, though X-ray pulsations have not been detected from this source.

We report the detection of a curved magnetic field in the ring-like shell of the bubble N4, derived from near-infrared polarization of reddened diskless stars located behind this bubble. The magnetic field in the shell is curved and parallel to the ring-like shell, and its strength is estimated to be $\sim 120\,\mu {\rm{G}}$ in the plane of the sky. The magnetic field strength in the shell is significantly enhanced compared to the local field strength. We calculate the mass-to-flux ratio for the submillimeter clumps in the shell and find that they are all magnetically subcritical. Our results demonstrate that the magnetic field strengthens as the interstellar medium is compressed into a shell, and suggest that the magnetic field has the potential to hinder star formation triggered by H ii region expansion.

We investigate the orbital histories of Virgo galaxies at various stages of H i gas stripping. In particular, we compare the location of galaxies with different H i morphology in phase space. This method is a great tool for tracing the gas stripping histories of galaxies as they fall into the cluster. Most galaxies at the early stage of H i stripping are found in the first infall region of Virgo, while galaxies undergoing active H i stripping mostly appear to be falling in or moving out near the cluster core for the first time. Galaxies with severely stripped, yet symmetric, H i disks are found in one of two locations. Some are deep inside the cluster, but others are found in the cluster outskirts with low orbital velocities. We suggest that the latter group of galaxies belong to a "backsplash" population. These present the clearest candidates for backsplashed galaxies observationally identified to date. We further investigate the distribution of a large sample of H i-detected galaxies toward Virgo in phase space, confirming that most galaxies are stripped of their gas as they settle into the gravitational potential of the cluster. In addition, we discuss the impact of tidal interactions between galaxies and group preprocessing on the H i properties of the cluster galaxies, and link the associated star formation evolution to the stripping sequence of cluster galaxies.

A full account of galaxy evolution in the context of ΛCDM cosmology requires measurements of the average star-formation rate (SFR) and cold gas abundance across cosmic time. Emission from the CO ladder traces cold gas, and [C ii] fine structure emission at $158\,\mu {\rm{m}}$ traces the SFR. Intensity mapping surveys the cumulative surface brightness of emitting lines as a function of redshift, rather than individual galaxies. CMB spectral distortion instruments are sensitive to both the mean and anisotropy of the intensity of redshifted CO and [C ii] emission. Large-scale anisotropy is proportional to the product of the mean surface brightness and the line luminosity-weighted bias. The bias provides a connection between galaxy evolution and its cosmological context, and is a unique asset of intensity mapping. Cross-correlation with galaxy redshift surveys allows unambiguous measurements of redshifted line brightness despite residual continuum contamination and interlopers. Measurement of line brightness through cross-correlation also evades cosmic variance and suggests new observation strategies. Galactic foreground emission is $\approx {10}^{3}$ times larger than the expected signals, and this places stringent requirements on instrument calibration and stability. Under a range of assumptions, a linear combination of bands cleans continuum contamination sufficiently that residuals produce a modest penalty over the instrumental noise. For PIXIE, the $2\sigma$ sensitivity to CO and [C ii] emission scales from $\approx 5\times {10}^{-2}\,\mathrm{kJy}\,{\mathrm{sr}}^{-1}$ at low redshift to $\approx 2\,\mathrm{kJy}\,{\mathrm{sr}}^{-1}$ by reionization.

Among the Milky Way satellites discovered in the past three years, Triangulum II has presented the most difficulty in revealing its dynamical status. Kirby et al. identified it as the most dark-matter-dominated galaxy known, with a mass-to-light ratio within the half-light radius of ${3600}_{-2100}^{+3500}\,{M}_{\odot }\,{L}_{\odot }^{-1}$. On the other hand, Martin et al. measured an outer velocity dispersion that is 3.5 ± 2.1 times larger than the central velocity dispersion, suggesting that the system might not be in equilibrium. From new multi-epoch Keck/DEIMOS measurements of 13 member stars in Triangulum II, we constrain the velocity dispersion to be ${\sigma }_{v}\lt 3.4$ km s⁻¹ (90% C.L.). Our previous measurement of ${\sigma }_{v}$, based on six stars, was inflated by the presence of a binary star with variable radial velocity. We find no evidence that the velocity dispersion increases with radius. The stars display a wide range of metallicities, indicating that Triangulum II retained supernova ejecta and therefore possesses, or once possessed, a massive dark matter halo. However, the detection of a metallicity dispersion hinges on the membership of the two most metal-rich stars. The stellar mass is lower than galaxies of similar mean stellar metallicity, which might indicate that Triangulum II is either a star cluster or a tidally stripped dwarf galaxy. Detailed abundances of one star show heavily depressed neutron-capture abundances, similar to stars in most other ultra-faint dwarf galaxies but unlike stars in globular clusters.

The aim of the present work is to unravel the radiolytic decomposition of adenine (C₅H₅N₅) under conditions relevant to the Martian surface. Being the fundamental building block of (deoxy)ribonucleic acids, the possibility of survival of this biomolecule on the Martian surface is of primary importance to the astrobiology community. Here, neat adenine and adenine–magnesium perchlorate mixtures were prepared and irradiated with energetic electrons that simulate the secondary electrons originating from the interaction of the galactic cosmic rays with the Martian surface. Perchlorates were added to the samples since they are abundant—and therefore relevant oxidizers on the surface of Mars—and they have been previously shown to facilitate the radiolysis of organics such as glycine. The degradation of the samples were monitored in situ via Fourier transformation infrared spectroscopy and the electron ionization quadruple mass spectrometric method; temperature-programmed desorption profiles were then collected by means of the state-of-the-art single photon photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), allowing for the detection of the species subliming from the sample. The results showed that perchlorates do increase the destruction rate of adenine by opening alternative reaction channels, including the concurrent radiolysis/oxidation of the sample. This new pathway provides a plethora of different radiolysis products that were identified for the first time. These are carbon dioxide (CO₂), isocyanic acid (HNCO), isocyanate (OCN⁻), carbon monoxide (CO), and nitrogen monoxide (NO); an oxidation product containing carbonyl groups (R₁R₂–C=O) with a constrained five-membered cyclic structure could also be observed. Cyanamide (H₂N–C≡N) was detected in both irradiated samples as well.

We present data on the gas-phase abundances for 9 different elements in the interstellar medium of the Small Magellanic Cloud (SMC), based on the strengths of ultraviolet absorption features over relevant velocities in the spectra of 18 stars within the SMC. From this information and the total abundances defined by the element fractions in young stars in the SMC, we construct a general interpretation on how these elements condense into solid form onto dust grains. As a group, the elements Si, S, Cr, Fe, Ni, and Zn exhibit depletion sequences similar to those in the local part of our Galaxy defined by Jenkins. The elements Mg and Ti deplete less rapidly in the SMC than in the Milky Way, and Mn depletes more rapidly. We speculate that these differences might be explained by the different chemical affinities to different existing grain substrates. For instance, there is evidence that the mass fractions of polycyclic aromatic hydrocarbons in the SMC are significantly lower than those in the Milky Way. We propose that the depletion sequences that we observed for the SMC may provide a better model for interpreting the element abundances in low-metallicity Damped Lyman Alpha (DLA) and sub-DLA absorption systems that are recorded in the spectra of distant quasars and gamma-ray burst afterglows.

We present pressure profiles of galaxy clusters determined from high-resolution Sunyaev–Zel'dovich (SZ) effect observations of 14 clusters, which span the redshift range of $0.25\lt z\lt 0.89$. The procedure simultaneously fits spherical cluster models to MUSTANG and Bolocam data. In this analysis, we adopt the generalized NFW parameterization of pressure profiles to produce our models. Our constraints on ensemble-average pressure profile parameters, in this study γ, C₅₀₀, and P₀, are consistent with those in previous studies, but for individual clusters we find discrepancies with the X-ray derived pressure profiles from the ACCEPT2 database. We investigate potential sources of these discrepancies, especially cluster geometry, electron temperature of the intracluster medium, and substructure. We find that the ensemble mean profile for all clusters in our sample is described by the parameters $[\gamma ,{C}_{500},{P}_{0}]=[{0.3}_{-0.1}^{+0.1},{1.3}_{-0.1}^{+0.1},{8.6}_{-2.4}^{+2.4}]$, cool core clusters are described by $[\gamma ,{C}_{500},{P}_{0}]\ =[{0.6}_{-0.1}^{+0.1},{0.9}_{-0.1}^{+0.1},{3.6}_{-1.5}^{+1.5}]$, and disturbed clusters are described by $[\gamma ,{C}_{500},{P}_{0}]=[{0.0}_{-0.0}^{+0.1},{1.5}_{-0.2}^{+0.1},{13.8}_{-1.6}^{+1.6}]$. Of the 14 clusters, 4 have clear substructure in our SZ observations, while an additional 2 clusters exhibit potential substructure.

We present results on the clustering properties of galaxies as a function of both stellar mass and specific star formation rate (sSFR) using data from the PRIMUS and DEEP2 galaxy redshift surveys spanning $0.2\lt z\lt 1.2$. We use spectroscopic redshifts of over 100,000 galaxies covering an area of 7.2 deg² over five separate fields on the sky, from which we calculate cosmic variance errors. We find that the galaxy clustering amplitude is as strong of a function of sSFR as of stellar mass, and that at a given sSFR, it does not significantly depend on stellar mass within the range probed here. We further find that within the star-forming population and at a given stellar mass, galaxies above the main sequence of star formation with higher sSFR are less clustered than galaxies below the main sequence with lower sSFR. We also find that within the quiescent population, galaxies with higher sSFR are less clustered than galaxies with lower sSFR, at a given stellar mass. We show that the galaxy clustering amplitude smoothly increases with both increasing stellar mass and decreasing sSFR, implying that galaxies likely evolve across the main sequence, not only along it, before galaxies eventually become quiescent. These results imply that the relation of stellar mass to halo mass, which connects galaxies to dark matter halos, likely depends on sSFR.

In this paper we present an analysis of absorption-line variability in mini-BAL quasar LBQS 1206+1052. The Sloan Digital Sky Survey spectrum demonstrates that the absorption troughs can be divided into two components of blueshift velocities of ∼700 and ∼1400 km s⁻¹ relative to the quasar rest frame. The former component shows rare Balmer absorption, which is an indicator of high-density absorbing gas; thus, the quasar is worth follow-up spectroscopic observations. Our follow-up optical and near-infrared spectra using MMT, YFOSC, TSpec, and DBSP reveal that the strengths of the absorption lines vary for both components, while the velocities do not change. We reproduce all of the spectral data by assuming that only the ionization state of the absorbing gas is variable and that all other physical properties are invariable. The variation of ionization is consistent with the variation of optical continuum from the V-band light curve. Additionally, we cannot interpret the data by assuming that the variability is due to a movement of the absorbing gas. Therefore, our analysis strongly indicates that the absorption-line variability in LBQS 1206+1052 is photoionization driven. As shown from photoionization simulations, the absorbing gas with blueshift velocity of ∼700 km s⁻¹ has a density in the range of 10⁹ to 10¹⁰ cm⁻³ and a distance of ∼1 pc, and the gas with blueshift velocity of ∼1400 km s⁻¹ has a density of 10³ cm⁻³ and a distance of ∼1 kpc.

We present a new model, MULTI-VP, which computes the three-dimensional structure of the solar wind and includes the chromosphere, the transition region, and the corona and low heliosphere. MULTI-VP calculates a large ensemble of wind profiles flowing along open magnetic field lines that sample the entire three-dimensional atmosphere or, alternatively, a given region of interest. The radial domain starts from the photosphere and typically extends to about $30\ {R}_{\odot }$. The elementary uni-dimensional wind solutions are based on a mature numerical scheme that was adapted in order to accept any flux-tube geometry. We discuss here the first results obtained with this model. We use Potential Field Source-surface extrapolations of magnetograms from the Wilcox Solar Observatory to determine the structure of the background magnetic field. Our results support the hypothesis that the geometry of the magnetic flux-tubes in the lower corona controls the distribution of slow and fast wind flows. The inverse correlation between density and speed far away from the Sun is a global effect resulting from small readjustments of the flux-tube cross-sections in the high corona (necessary to achieve global pressure balance and a uniform open flux distribution). In comparison to current global MHD models, MULTI-VP performs much faster and does not suffer from spurious cross-field diffusion effects. We show that MULTI-VP has the capability to predict correctly the dynamical and thermal properties of the background solar wind (wind speed, density, temperature, magnetic field amplitude, and other derived quantities) and to approach real-time operation requirements.

We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H] = −2 dex. Our abundances range from $-2.66\leqslant [\mathrm{Fe}/{\rm{H}}]\leqslant -1.40$ dex with conservative uncertainties of 0.07 dex. We find an average [α/Fe] = 0.34 ± 0.09 dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and $\langle 3{\rm{D}}\rangle$ hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work.

Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Within the standard Sweet–Parker model, this process would be too slow to explain observations (e.g., solar flares). In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen-in field lines and magnetic reconnection. In the presence of turbulence, the reconnection is independent of microscopic plasma properties and may be much faster than previously thought, as proposed in Lazarian & Vishniac and tested in Kowal et al. However, the considered turbulence in the Lazarian–Vishniac model was imposed externally. In this work, we consider reconnection-driven magnetized turbulence in realistic three-dimensional geometry initiated by stochastic noise. We demonstrate through numerical simulations that the stochastic reconnection is able to self-generate turbulence through interactions between the reconnection outflows. We analyze the statistical properties of velocity fluctuations using power spectra and anisotropy scaling in the local reference frame, which demonstrates that the reconnection produces Kolmogorov-like turbulence, compatible with the Goldreich & Sridhar model. Anisotropy statistics are, however, strongly affected by the dynamics of flows generated by the reconnection process. Once the broad turbulent region is formed, the typical anisotropy scaling ${l}_{\parallel }\propto {l}_{\perp }^{2/3}$ is formed, especially for high resolution models, where the broader range of scales is available. The decay of reconnection outflows to turbulent-like fluctuations, characterized by different anisotropy scalings, strongly depends on the β plasma parameter. Moreover, the estimated reconnection rates are weakly dependent on the model resolution, suggesting that no external processes are required to make reconnection fast.

High-dispersion coronagraphy (HDC) optimally combines high-contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway toward fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, and on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.

The geometry and intrinsic ellipticity distribution of ultra-diffuse galaxies (UDG) is determined from the line-of-sight distribution of axial ratios q of a large sample of UDGs, detected by Koda et al. in the Coma cluster. With high significance, the data rules out an oblate, disk-like geometry, characterized by major axes a = b > c. The data is, however, in good agreement with prolate shapes, corresponding to a = b < c. This indicates that UDGs are not thickened, rotating, axisymmetric disks, puffed up by violent processes. Instead, they are anisotropic elongated cigar- or bar-like structures, similar to the prolate dwarf spheroidal galaxy population of the Local Group. The intrinsic distribution of axial ratios of the Coma UDGs is flat in the range of 0.4 ≤ a/c ≤ 0.9 with a mean value of $\langle a/c\rangle =0.65\pm 0.14$. This might provide important constraints for theoretical models of their origin. Formation scenarios that could explain the extended prolate nature of UDGs are discussed.

We report the detection of morphology-dependent stellar age in massive quenched galaxies (QGs) at z ∼ 1.2. The sense of the dependence is that compact QGs are 0.5–2 Gyr older than normal-sized ones. The evidence comes from three different age indicators—${D}_{n}4000$, ${{\rm{H}}}_{\delta }$, and fits to spectral synthesis models—applied to their stacked optical spectra. All age indicators consistently show that the stellar populations of compact QGs are older than those of their normal-sized counterparts. We detect weak [O ii] emission in a fraction of QGs, and the strength of the line, when present, is similar between the two samples; however, compact galaxies exhibit a significantly lower frequency of [O ii] emission than normal ones. Fractions of both samples are individually detected in 7 Ms Chandra X-ray images (luminosities ∼10⁴⁰–10⁴¹ erg s⁻¹). The 7 Ms stacks of nondetected galaxies show similarly low luminosities in the soft band only, consistent with a hot gas origin for the X-ray emission. While both [O ii] emitters and nonemitters are also X-ray sources among normal galaxies, no compact galaxy with [O ii] emission is an X-ray source, arguing against an active galactic nucleus (AGN) powering the line in compact galaxies. We interpret the [O ii] properties as further evidence that compact galaxies are older and further along in the process of quenching star formation and suppressing gas accretion. Finally, we argue that the older age of compact QGs is evidence of progenitor bias: compact QGs simply reflect the smaller sizes of galaxies at their earlier quenching epoch, with stellar density most likely having nothing directly to do with cessation of star formation.

Scattering on a multi-level atomic system has dominant contributions from resonance and Raman scattering. While initial and final levels are the same for resonance scattering, they are different for Raman scattering. The frequency redistribution for resonance scattering is described by the usual partial frequency redistribution functions of Hummer, while that for Raman scattering is described by cross-redistribution (XRD) function. In the present paper, we investigate the importance of XRD on linear polarization profiles of ³P−³S triplets of Mg i and Ca i formed in an isothermal one-dimensional atmosphere. We show that XRD produces significant effects on the linear polarization profiles when the wavelength separations between the line components of the multiplet are small, like in the cases of Mg i b and Ca i triplets.

Despite decades of effort, the timing and duration of He ii reionization and the properties of the quasars believed to drive it are still not well constrained. We present a new method to study both via the thermal proximity effect—the heating of the intergalactic medium (IGM) around quasars when their radiation doubly ionizes helium. We post-process hydrodynamical simulations with 1D radiative transfer and study how the thermal proximity effect depends on the He ii fraction, ${x}_{\mathrm{He}{\rm{II}},0}$, which prevailed in the IGM before the quasar turned on, and the quasar lifetime ${t}_{{\rm{Q}}}$. We find that the amplitude of the temperature boost in the quasar environment depends on ${x}_{\mathrm{He}{\rm{II}},0}$, with a characteristic value of ${\rm{\Delta }}T\simeq {10}^{4}\,{\rm{K}}$ for ${x}_{\mathrm{He}{\rm{II}},0}=1.0$, whereas the size of the thermal proximity zone is sensitive to ${t}_{{\rm{Q}}}$, with typical sizes of $\simeq 100\,\mathrm{cMpc}$ for ${t}_{{\rm{Q}}}={10}^{8}\,\mathrm{yr}$. This temperature boost increases the thermal broadening of H i absorption lines near the quasar. We introduce a new Bayesian statistical method based on measuring the Lyα forest power spectrum as a function of distance from the quasar, and demonstrate that the thermal proximity effect should be easily detectable. For a mock data set of 50 quasars at $z\simeq 4$, we predict that one can measure ${x}_{\mathrm{He}{\rm{II}},0}$ to an (absolute) precision $\approx 0.04$ and ${t}_{{\rm{Q}}}$ to a precision of $\approx 0.1$ dex. By applying our formalism to existing high-resolution Lyα forest spectra, one should be able to reconstruct the He ii reionization history, providing a global census of hard photons in the high-z universe.

We report Very Large Array observations at 7 mm, 9 mm, and 3 cm toward the pre-transitional disk of the Herbig Ae star HD 169142. These observations have allowed us to study the millimeter emission of this disk with the highest angular resolution so far (012 × 009, or 14 au × 11 au, at 7 mm). Our 7 and 9 mm images show a narrow ring of emission at a radius of ∼25 au tracing the outer edge of the inner gap. This ring presents an asymmetric morphology that could be produced by dynamical interactions between the disk and forming planets. Additionally, the azimuthally averaged radial intensity profiles of the 7 and 9 mm images confirm the presence of the previously reported gap at ∼45 au and reveal a new gap at ∼85 au. We analyzed archival DCO⁺(3–2) and C¹⁸O(2–1) ALMA observations, showing that the CO snowline is located very close to this third outer gap. This suggests that growth and accumulation of large dust grains close to the CO snowline could be the mechanism responsible for this proposed outer gap. Finally, a compact source of emission is detected at 7 mm, 9 mm, and 3 cm toward the center of the disk. Its flux density and spectral index indicate that it is dominated by free–free emission from ionized gas, which could be associated with the photoionization of the inner disk, an independent object, or an ionized jet.

The discovery of the ultraluminous X-ray pulsar M82 X-2 has stimulated lively discussion on the nature of the accreting neutron star. In most of the previous studies the magnetic field of the neutron star was derived from the observed spin-up/down rates based on the standard thin, magnetized accretion disk model. However, under super-Eddington accretion the inner part of the accretion disk becomes geometrically thick. In this work we consider both radiation feedback from the neutron star and the sub-Keplerian rotation in a thick disk and calculate the magnetic moment–mass accretion rate relations for the measured rates of spin change. We find that the derived neutron star's dipole magnetic field depends on the maximum accretion rate adopted, but is likely ≲10¹³ G. The predicted accretion rate change can be used to test the proposed models by comparison with observations.

We present results from a non-cosmological, three-dimensional hydrodynamical simulation of the gas in the dwarf spheroidal galaxy Ursa Minor. Assuming an initial baryonic-to-dark-matter ratio derived from the cosmic microwave background radiation, we evolved the galactic gas distribution over 3 Gyr, taking into account the effects of the types Ia and II supernovae. For the first time, we used in our simulation the instantaneous supernovae rates derived from a chemical evolution model applied to spectroscopic observational data of Ursa Minor. We show that the amount of gas that is lost in this process is variable with time and radius, being the highest rates observed during the initial 600 Myr in our simulation. Our results indicate that types Ia and II supernovae must be essential drivers of the gas loss in Ursa Minor galaxy (and probably in other similar dwarf galaxies), but it is ultimately the combination of galactic winds powered by these supernovae and environmental effects (e.g., ram-pressure stripping) that results in the complete removal of the gas content.

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star's surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that if the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.

Ellerman bombs (EBs) are a kind of solar activity that is suggested to occur in the lower solar atmosphere. Recent observations using the Interface Region Imaging Spectrograph (IRIS) show connections between EBs and IRIS bombs (IBs), which imply that EBs might be heated to a much higher temperature (8 × 10⁴ K) than previous results. Here we perform a spectral analysis of EBs simultaneously observed by the Fast Imaging Solar Spectrograph and IRIS. The observational results show clear evidence of heating in the lower atmosphere, indicated by the wing enhancement in Hα, Ca ii 8542 Å, and Mg ii triplet lines and also by brightenings in images of the 1700 Å and 2832 Å ultraviolet continuum channels. Additionally, the intensity of the Mg ii triplet line is correlated with that of Hα when an EB occurs, suggesting the possibility of using the triplet as an alternative way to identify EBs. However, we do not find any signal in IRIS hotter lines (C ii and Si iv). For further analysis, we employ a two-cloud model to fit the two chromospheric lines (Hα and Ca ii 8542 Å) simultaneously, and obtain a temperature enhancement of 2300 K for a strong EB. This temperature is among the highest of previous modeling results, albeit still insufficient to produce IB signatures at ultraviolet wavelengths.

IC 630 is a nearby early-type galaxy with a mass of $6\times {10}^{10}$M_⊙ with an intense burst of recent (6 Myr) star formation (SF). It shows strong nebular emission lines, with radio and X-ray emission, which classifies it as an active galactic nucleus (AGN). With VLT-SINFONI and Gemini North-NIFS adaptive optics observations (plus supplementary ANU 2.3 m WiFeS optical IFU observations), the excitation diagnostics of the nebular emission species show no sign of standard AGN engine excitation; the stellar velocity dispersion also indicates that a supermassive black hole (if one is present) is small (${M}_{\bullet }=2.25\times {10}^{5}\,{M}_{\odot }$). The luminosity at all wavelengths is consistent with SF at a rate of about 1–2 M_⊙ yr⁻¹. We measure gas outflows driven by SF at a rate of 0.18 M_⊙ yr⁻¹ in a face-on truncated cone geometry. We also observe a nuclear cluster or disk and other clusters. Photoionization from young, hot stars is the main excitation mechanism for [Fe ii] and hydrogen, whereas shocks are responsible for the H₂ excitation. Our observations are broadly comparable with simulations where a Toomre-unstable, self-gravitating gas disk triggers a burst of SF, peaking after about 30 Myr and possibly cycling with a period of about 200 Myr.

Dynamical friction is thought to be a principal mechanism responsible for orbital evolution of massive black holes (MBHs) in the aftermath of galactic mergers and an important channel for formation of gravitationally bound MBH binaries. We use 2D radiative hydrodynamic simulations to investigate the efficiency of dynamical friction in the presence of radiative feedback from an MBH moving through a uniform density gas. We find that ionizing radiation that emerges from the innermost parts of the MBH's accretion flow strongly affects the dynamical friction wake and renders dynamical friction inefficient for a range of physical scenarios. MBHs in this regime tend to experience positive net acceleration, meaning that they speed up, contrary to the expectations for gaseous dynamical friction in absence of radiative feedback. The magnitude of this acceleration is however negligibly small and should not significantly alter the velocity of MBHs over relevant physical timescales. Our results suggest that suppression of dynamical friction is more severe at the lower mass end of the MBH spectrum which, compounded with inefficiency of the gas drag for lower mass objects in general, implies that <10⁷${M}_{\odot }$ MBHs have fewer means to reach the centers of merged galaxies. These findings provide formulation for a sub-resolution model of dynamical friction in presence of MBH radiative feedback that can be easily implemented in large scale simulations.

Open magnetic flux in the heliosphere is determined from the radial component of the magnetic field vector measured onboard interplanetary space probes. Previous Ulysses research has shown remarkable independence of the flux density from heliographic latitude, explained by super-radial expansion of plasma. Here we are investigating whether any longitudinal variation exists in the 50 year long OMNI magnetic data set. The heliographic longitude of origin of the plasma package was determined by applying a correction according to the solar wind travel time. Significant recurrent enhancements of the magnetic flux density were observed throughout solar cycle 23, lasting for several years. Similar, long-lasting recurring features were observed in the solar wind velocity, temperature and the deviation angle of the solar wind velocity vector from the radial direction. Each of the recurrent features has a recurrence period slightly differing from the Carrington rotation rate, although they show a common trend in time. Examining the coronal temperature data of ACE leads to the possible explanation that these long-term structures are caused by slow–fast solar wind interaction regions. A comparison with MESSENGER data measured at 0.5 au shows that these longitudinal magnetic modulations do not exist closer to the Sun, but are the result of propagation.

We investigate the recent star formation history (SFH) in the inner region of 57 nearly face-on spiral galaxies selected from the Calar Alto Legacy Integral Field Area (CALIFA) survey. For each galaxy, we use the integral field spectroscopy from CALIFA to obtain two-dimensional maps and radial profiles of three parameters that are sensitive indicators of the recent SFH: the 4000 Å break (D_n(4000)), and the equivalent width of Hδ absorption ($\mathrm{EW}({\rm{H}}{\delta }_{A})$) and Hα emission (EW(Hα)). We have also performed photometric decomposition of bulge/bar/disk components based on SDSS optical image. We identify a class of 17 "turnover" galaxies for which the central region presents a significant drop in D_n(4000), and most of them correspondingly show a central upturn in $\mathrm{EW}({\rm{H}}{\delta }_{A})$ and EW(Hα). This indicates that the central region of the turnover galaxies has experienced star formation in the past 1–2 Gyr, which makes the bulge younger and more star-forming than surrounding regions. We find that almost all (15/17) of the turnover galaxies are barred, while only half of the barred galaxies in our sample (15/32) are classified as a turnover galaxies. This finding provides strong evidence in support of the theoretical expectation that the bar may drive gas from the disk inward to trigger star formation in the galaxy center, an important channel for the growth/rejuvenation of pseudobulges in disk galaxies.

How the four terrestrial planets of the solar system formed is one of the most fundamental questions in the planetary sciences. Particularly, the formation of Mercury remains poorly understood. We investigated terrestrial planet formation by performing 110 high-resolution N-body simulation runs using more than 100 embryos and 6000 disk planetesimals representing a primordial protoplanetary disk. To investigate the formation of Mercury, these simulations considered an inner region of the disk at 0.2–0.5 au (the Mercury region) and disks with and without mass enhancements beyond the ice line location, a_IL, in the disk, where a_IL = 1.5, 2.25, and 3.0 au were tested. Although Venus and Earth analogs (considering both orbits and masses) successfully formed in the majority of the runs, Mercury analogs were obtained in only nine runs. Mars analogs were also similarly scarce. Our Mercury analogs concentrated at orbits with a ∼ 0.27–0.34 au, relatively small eccentricities/inclinations, and median mass m ∼ 0.2 ${M}_{\oplus }$. In addition, we found that our Mercury analogs acquired most of their final masses from embryos/planetesimals initially located between 0.2 and ∼1–1.5 au within 10 Myr, while the remaining mass came from a wider region up to ∼3 au at later times. Although the ice line was negligible in the formation of planets located in the Mercury region, it enriched all terrestrial planets with water. Indeed, Mercury analogs showed a wide range of water mass fractions at the end of terrestrial planet formation.

Pulsating stars, such as Cepheids, Miras, and RR Lyrae stars, are important distance indicators and calibrators of the "cosmic distance ladder," and yet their period–luminosity–metallicity (PLZ) relations are still constrained using simple statistical methods that cannot take full advantage of available data. To enable optimal usage of data provided by the Gaia mission, we present a probabilistic approach that simultaneously constrains parameters of PLZ relations and uncertainties in Gaia parallax measurements. We demonstrate this approach by constraining PLZ relations of type ab RR Lyrae stars in near-infrared W1 and W2 bands, using Tycho-Gaia Astrometric Solution (TGAS) parallax measurements for a sample of ≈100 type ab RR Lyrae stars located within 2.5 kpc of the Sun. The fitted PLZ relations are consistent with previous studies, and in combination with other data, deliver distances precise to 6% (once various sources of uncertainty are taken into account). To a precision of 0.05 mas (1σ), we do not find a statistically significant offset in TGAS parallaxes for this sample of distant RR Lyrae stars (median parallax of 0.8 mas and distance of 1.4 kpc). With only minor modifications, our probabilistic approach can be used to constrain PLZ relations of other pulsating stars, and we intend to apply it to Cepheid and Mira stars in the near future.

The discovery and subsequent study of optical counterparts to transient sources is crucial for their complete astrophysical understanding. Various gamma-ray burst (GRB) detectors, and more notably the ground-based gravitational wave detectors, typically have large uncertainties in the sky positions of detected sources. Searching these large sky regions spanning hundreds of square degrees is a formidable challenge for most ground-based optical telescopes, which can usually image less than tens of square degrees of the sky in a single night. We present algorithms for better scheduling of such follow-up observations in order to maximize the probability of imaging the optical counterpart, based on the all-sky probability distribution of the source position. We incorporate realistic observing constraints such as the diurnal cycle, telescope pointing limitations, available observing time, and the rising/setting of the target at the observatory's location. We use simulations to demonstrate that our proposed algorithms outperform the default greedy observing schedule used by many observatories. Our algorithms are applicable for follow-up of other transient sources with large positional uncertainties, such as Fermi-detected GRBs, and can easily be adapted for scheduling radio or space-based X-ray follow-up.

This paper is the first in a series, presenting a new galaxy cluster finder based on a three-dimensional Voronoi Tesselation plus a maximum likelihood estimator, followed by gapping-filtering in radial velocity(VoML+G). The scientific aim of the series is a reassessment of the diversity of optical clusters in the local universe. A mock galaxy database mimicking the southern strip of the magnitude(blue)-limited 2dF Galaxy Redshift Survey (2dFGRS), for the redshift range 0.009 < z < 0.22, is built on the basis of the Millennium Simulation of the LCDM cosmology and a reference catalog of "Millennium clusters," spannning across the 1.0 × 10¹²–1.0 × 10¹⁵M_⊙h⁻¹ dark matter (DM) halo mass range, is recorded. The validation of VoML+G is performed through its application to the mock data and the ensuing determination of the completeness and purity of the cluster detections by comparison with the reference catalog. The execution of VoML+G over the 2dFGRS mock data identified 1614 clusters, 22% with N_g ≥ 10, 64 percent with 10 > N_g ≥ 5, and 14% with N_g < 5. The ensemble of VoML+G clusters has a ∼59% completeness and a ∼66% purity, whereas the subsample with N_g ≥ 10, to z ∼ 0.14, has greatly improved mean rates of ∼75% and ∼90%, respectively. The VoML+G cluster velocity dispersions are found to be compatible with those corresponding to "Millennium clusters" over the 300–1000 km s⁻¹ interval, i.e., for cluster halo masses in excess of ∼3.0 × 10¹³M_⊙h⁻¹.

We present and analyze a rich data set including Subaru/SuprimeCam, HST/Advanced Camera for Surveys and Wide Field Camera 3, Keck/DEIMOS, Chandra/ACIS-I, and JVLA/C and D array for the merging cluster of galaxies ZwCl 0008.8+5215. With a joint Subaru+HST weak gravitational lensing analysis, we identify two dominant subclusters and estimate the masses to be ${M}_{200}={5.7}_{-1.8}^{+2.8}\times {10}^{14}\,{M}_{\odot }$ and ${1.2}_{-0.6}^{+1.4}\times {10}^{14}\,{M}_{\odot }$. We estimate the projected separation between the two subclusters to be ${924}_{-206}^{+243}\,\mathrm{kpc}$. We perform a clustering analysis of spectroscopically confirmed cluster member galaxies and estimate the line-of-sight velocity difference between the two subclusters to be $92\pm 164\,\mathrm{km}\,{{\rm{s}}}^{-1}$. We further motivate, discuss, and analyze the merger scenario through an analysis of the 42 ks of Chandra/ACIS-I and JVLA/C and D array polarization data. The X-ray surface brightness profile reveals a merging gas-core reminiscent of the Bullet Cluster. The global X-ray luminosity in the 0.5–7.0 keV band is $1.7\pm 0.1\times {10}^{44}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ and the global X-ray temperature is 4.90 ± 0.13 keV. The radio relics are polarized up to $40 \%$, and along with the masses, velocities, and positions of the two subclusters, we input these quantities into a Monte Carlo dynamical analysis and estimate the merger velocity at pericenter to be ${1800}_{-300}^{+400}\,\mathrm{km}\,{{\rm{s}}}^{-1}$. This is a lower-mass version of the Bullet Cluster and therefore may prove useful in testing alternative models of dark matter (DM). We do not find significant offsets between DM and galaxies, but the uncertainties are large with the current lensing data. Furthermore, in the east, the BCG is offset from other luminous cluster galaxies, which poses a puzzle for defining DM–galaxy offsets.

Direct collapse black holes (DCBHs) are excellent candidates for seeds of supermassive black holes observed at z ≳ 6. The formation of a DCBH requires a strong external radiation field to suppress H₂ formation and cooling in a collapsing gas cloud. Such a strong field is not easily achieved by first stars or normal star-forming galaxies. Here we investigate a scenario in which a previously formed DCBH can provide the necessary radiation field for the formation of additional ones. Using a one-zone model and simulated DCBH Spectral Energy Distributions (SEDs) filtered through absorbing gas initially having column density N_H, we derive the critical field intensity, ${J}_{\mathrm{LW}}^{\mathrm{crit}}$, to suppress H₂ formation and cooling. For the SED model with ${N}_{{\rm{H}}}=1.3\times {10}^{25}$ cm⁻², 8.0 × 10²⁴ cm⁻², and 5.0 × 10²⁴ cm⁻², we obtain ${J}_{\mathrm{LW}}^{\mathrm{crit}}\approx 22$, 35, and 54, all much smaller than the critical field intensity for normal star-forming galaxies ${J}_{\mathrm{LW}}^{\mathrm{crit}}\gtrsim 1000$ X-ray photons from previously formed DCBHs build up a high-z X-ray background (XRB) that may boost the ${J}_{\mathrm{LW}}^{\mathrm{crit}}$. However, we find that in the three SED models, ${J}_{\mathrm{LW}}^{\mathrm{crit}}$ only increases to ≈80, 170, and 390, even when ${\dot{\rho }}_{\bullet }$ reaches the maximum value allowed by the present-day XRB level (0.22, 0.034, 0.006 M_⊙ yr⁻¹ Mpc⁻³), which is still much smaller than the galactic value. Although considering the XRB from first galaxies may further increase ${J}_{\mathrm{LW}}^{\mathrm{crit}}$, we conclude that our investigation supports a scenario in which DCBHs may be more abundant than predicted by models only including galaxies as external radiation sources.

Polarized emission from polycyclic aromatic hydrocarbons (PAHs) potentially provides a new way to test the basic physics of the alignment of ultrasmall grains. In this paper, we present a new model of polarized PAH emission that takes into account the effect of PAH alignment with the magnetic field. We first generate a large sample of the grain angular momentum ${\boldsymbol{J}}$ by simulating the alignment of PAHs due to resonance paramagnetic relaxation that accounts for various interaction processes. We then calculate the polarization level of the PAH emission features for the different phases of the interstellar medium, including the cold neutral medium (CNM), reflection nebulae (RNe), and photodissociation regions. We find that a moderate degree of PAH alignment can significantly enhance the polarization degree of the PAH emission compared to the previous results obtained with randomly oriented angular momentum. In particular, we find that the smallest negatively charged PAHs in RNe can be excited to slightly suprathermal rotation due to enhanced ion collisional excitation, resulting in an increase of the polarization with the ionization fraction. Our results suggest that an RN is the most favorable environment in which to observe polarized PAH emission and to test the alignment physics of nanoparticles. Finally, we present an explicit relationship between the polarization level of PAH emission and the degree of external alignment for the CNM and RNe. The obtained relationship will be particularly useful for testing the alignment physics of PAHs in future observations.

Models for the evolution of the solar coronal magnetic field are vital for understanding solar activity, yet the best measurements of the magnetic field lie at the photosphere, necessitating the development of coronal models which are "data-driven" at the photosphere. We present an investigation to determine the feasibility and accuracy of such methods. Our validation framework uses a simulation of active region (AR) formation, modeling the emergence of magnetic flux from the convection zone to the corona, as a ground-truth data set, to supply both the photospheric information and to perform the validation of the data-driven method. We focus our investigation on how the accuracy of the data-driven model depends on the temporal frequency of the driving data. The Helioseismic and Magnetic Imager on NASA's Solar Dynamics Observatory produces full-disk vector magnetic field measurements at a 12-minute cadence. Using our framework we show that ARs that emerge over 25 hr can be modeled by the data-driving method with only ∼1% error in the free magnetic energy, assuming the photospheric information is specified every 12 minutes. However, for rapidly evolving features, under-sampling of the dynamics at this cadence leads to a strobe effect, generating large electric currents and incorrect coronal morphology and energies. We derive a sampling condition for the driving cadence based on the evolution of these small-scale features, and show that higher-cadence driving can lead to acceptable errors. Future work will investigate the source of errors associated with deriving plasma variables from the photospheric magnetograms as well as other sources of errors, such as reduced resolution, instrument bias, and noise.

Compact substructure is expected to arise in a starless core as mass becomes concentrated in the central region likely to form a protostar. Additionally, multiple peaks may form if fragmentation occurs. We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of 60 starless and protostellar cores in the Ophiuchus molecular cloud. We detect eight compact substructures which are $\gt 15^{\prime\prime}$ from the nearest Spitzer young stellar object. Only one of these has strong evidence for being truly starless after considering ancillary data, e.g., from Herschel and X-ray telescopes. An additional extended emission structure has tentative evidence for starlessness. The number of our detections is consistent with estimates from a combination of synthetic observations of numerical simulations and analytical arguments. This result suggests that a similar ALMA study in the Chamaeleon I cloud, which detected no compact substructure in starless cores, may be due to the peculiar evolutionary state of cores in that cloud.

Using data from the NASA spacecraft Kepler, we study solar-like oscillations in red giant stars in the open cluster NGC 6811. We determine oscillation frequencies, frequency separations, period spacings of mixed modes, and mode visibilities for eight cluster giants. The oscillation parameters show that these stars are helium-core-burning red giants. The eight stars form two groups with very different oscillation power spectra; the four stars with the lowest Δν values display rich sets of mixed l = 1 modes, while this is not the case for the four stars with higher Δν. For the four stars with lowest Δν, we determine the asymptotic period spacing of the mixed modes, ΔP, which together with the masses we derive for all eight stars suggest that they belong to the so-called secondary clump. Based on the global oscillation parameters, we present initial theoretical stellar modeling that indicates that we can constrain convective-core overshoot on the main sequence and in the helium-burning phase for these ∼2 M_⊙ stars. Finally, our results indicate less mode suppression than predicted by recent theories for magnetic suppression of certain oscillation modes in red giants.

We investigate the formation and early evolution of star clusters, assuming that they form from a turbulent starless clump of a given mass bounded inside a parent self-gravitating molecular cloud characterized by a particular mass surface density. As a first step, we assume instantaneous star cluster formation and gas expulsion. We draw our initial conditions from observed properties of starless clumps. We follow the early evolution of the clusters up to 20 Myr, investigating the effects of different star formation efficiencies, primordial binary fractions and eccentricities, and primordial mass segregation levels. We investigate clumps with initial masses of ${M}_{\mathrm{cl}}=3000\,{M}_{\odot }$ embedded in ambient cloud environments with mass surface densities ${{\rm{\Sigma }}}_{\mathrm{cloud}}=0.1$ and $1\,{\rm{g}}\,{\mathrm{cm}}^{-2}$. We show that these models of fast star cluster formation result, in the fiducial case, in clusters that expand rapidly, even considering only the bound members. Clusters formed from higher ${{\rm{\Sigma }}}_{\mathrm{cloud}}$ environments tend to expand more quickly and thus are soon larger than clusters born from lower ${{\rm{\Sigma }}}_{\mathrm{cloud}}$ conditions. To form a young cluster of a given age, stellar mass, and mass surface density, these models need to assume a parent molecular clump that is many times denser, which is unrealistic compared to observed systems. We also show that, in these models, the initial binary properties are only slightly modified by interactions, meaning that the binary properties, e.g., at 20 Myr, are very similar to those at birth. With this study, we set up the foundation for future work, where we will investigate more realistic models of star formation compared to this instantaneous, baseline case.

Growing supermassive black holes ($\sim {10}^{9}\,{M}_{\odot }$) that power luminous $z\gt 6$ quasars from light seeds—the remnants of the first stars—within a Gyr of the Big Bang poses a timing challenge. The formation of massive black hole seeds via direct collapse with initial masses $\sim {10}^{4}\mbox{--}{10}^{5}\,{M}_{\odot }$ alleviates this problem. Viable direct-collapse black hole formation sites, the satellite halos of star-forming galaxies, merge and acquire stars to produce a new, transient class of high-redshift objects, obese black hole galaxies (OBGs). The accretion luminosity outshines that of the stars in OBGs. We predict the multi-wavelength energy output of OBGs and growing Pop III remnants at z = 9 for standard and slim disk accretion, as well as high and low metallicities of the associated stellar population. We derive robust selection criteria for OBGs—a pre-selection to eliminate blue sources, followed by color–color cuts $([{F}_{090W}-{F}_{220W}]\gt 0;-0.3\lt [{F}_{200W}-{F}_{444W}]\lt 0.3)$ and the ratio of X-ray flux to rest-frame optical flux $({F}_{X}/{F}_{444W}\gg 1)$. Our cuts sift out OBGs from other bright, high- and low-redshift contaminants in the infrared. OBGs with predicted ${M}_{{AB}}\lt 25$ are unambiguously detectable by the Mid-Infrared Instrument (MIRI), on the upcoming James Webb Space Telescope (JWST). For parameters explored here, growing Pop III remnants with predicted ${M}_{{AB}}\lt 30$ will likely be undetectable by JWST. We demonstrate that JWST has the power to discriminate between initial seeding mechanisms.

The energy in turbulent flow can be amplified by compression, when the compression occurs on a timescale shorter than the turbulent dissipation time. This mechanism may play a part in sustaining turbulence in various astrophysical systems, including molecular clouds. The amount of turbulent amplification depends on the net effect of the compressive forcing and turbulent dissipation. By giving an argument for a bound on this dissipation, we give a lower bound for the scaling of the turbulent velocity with the compression ratio in compressed turbulence. That is, turbulence undergoing compression will be enhanced at least as much as the bound given here, subject to a set of caveats that will be outlined. Used as a validation check, this lower bound suggests that some models of compressing astrophysical turbulence are too dissipative. The technique used highlights the relationship between compressed turbulence and decaying turbulence.

We investigate the far-infrared (far-IR) properties of galaxies selected via deep, narrow-band imaging of the Hα emission line in four redshift slices from $z=0.40\mbox{--}2.23$ over ∼1 deg² as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the Herschel PACS/SPIRE far-IR bands, along with $850\,\mu {\rm{m}}$ imaging from SCUBA-2 and Very Large Array 1.4 GHz imaging, to study the evolution of the dust properties of Hα-emitters selected above an evolving characteristic luminosity threshold, $0.2{L}_{{\rm{H}}\alpha }^{\star }(z)$. We investigate the relationship between the dust temperatures, T_dust, and the far-infrared luminosities, L_IR, of our stacked samples, finding that our Hα-selection identifies cold, low-L_IR galaxies (${T}_{\mathrm{dust}}\sim 14$ K; $\mathrm{log}[{L}_{\mathrm{IR}}/{L}_{\odot }]\sim 9.9$) at z = 0.40, and more luminous, warmer systems (${T}_{\mathrm{dust}}\sim 34$ K; $\mathrm{log}[{L}_{\mathrm{IR}}/{L}_{\odot }]\sim 11.5$) at z = 2.23. Using a modified graybody model, we estimate "characteristic sizes" for the dust-emitting regions of Hα-selected galaxies of ∼0.5 kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy interstellar medium structure. Lastly, we use measurements of the dust masses from our far-IR stacking along with metallicity-dependent gas-to-dust ratios (${\delta }_{\mathrm{GDR}}$) to measure typical molecular gas masses of $\sim 1\times {10}^{10}\,{M}_{\odot }$ for these bright Hα-emitters. The gas depletion timescales are shorter than the Hubble time at each redshift, suggesting probable replenishment of their gas reservoirs from the intergalactic medium. Based on the number density of Hα-selected galaxies, we find that typical star-forming galaxies brighter than $0.2{L}_{{\rm{H}}\alpha }^{\star }(z)$ comprise a significant fraction (35 ± 10%) of the total gas content of the universe, consistent with the predictions of the latest state-of-the-art cosmological simulations.

We present a long-term spectral monitoring of the unique double pulsar binary PSR J0737-3039 corresponding to two "Large Programs" performed by XMM-Newton in 2006 and 2011. Spectral variability of pulsar emission in soft X-rays is not evident over 5 years, despite the significant relativistic spin precession in the considered time span ($\sim 25^\circ$). We provide, for the first time, evidence of hard X-ray emission from the system in the 5–8 keV energy band. The standard spectral analysis was coupled to the energy dependent spatial analysis to confirm this excess, most likely ascribed to iron line emission. The Fe Kα emission line at 6.4–6.97 keV was previously unheard of in non-accreting binary systems and could testify to the presence of a relic disk that survived the supernova explosions that terminated the lives of the double pulsar's stellar progenitors. The existence of a relic disk in this system reinforces speculation about the presence of similar structures around other peculiar classes of isolated neutron stars.

We present Submillimeter Array 880 μm dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores and the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields a plane-of-sky magnetic field strength of 0.4–1.7 mG for the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that the gravitational energy in the filament dominates magnetic and kinematic energies, while the kinematic energy dominates in the cores. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores.

The starspots on the surface of many chromospherically active binary stars concentrate on long-lived active longitudes separated by 180°. Shifts in activity between these two longitudes, the "flip-flop" events, have been observed in single stars like FK Comae and binary stars like σ Geminorum. Recently, interferometry has revealed that ellipticity may at least partly explain the flip-flop events in σ Geminorum. This idea was supported by the double-peaked shape of the long-term mean light curve of this star. Here we show that the long-term mean light curves of 14 chromospherically active binaries follow a general model that explains the connection between orbital motion, changes in starspot distribution, ellipticity, and flip-flop events. Surface differential rotation is probably weak in these stars, because the interference of two constant period waves may explain the observed light curve changes. These two constant periods are the active longitude period $({P}_{\mathrm{act}})$ and the orbital period $({P}_{\mathrm{orb}})$. We also show how to apply the same model to single stars, where only the value of P_act is known. Finally, we present a tentative interference hypothesis about the origin of magnetic fields in all spectral types of stars.

The Sculptor dwarf spheroidal galaxy appears to contain two distinct stellar populations of differing metallicity. Several authors have argued that in order for these two populations to reside in the same gravitational potential, the dark matter halo must have a core similar to that observed in the stellar count profile. This would exclude cuspy Navarro–Frenk–White (NFW) density profiles of the kind predicted for halos and subhalos by dark matter-only simulations of the ΛCDM cosmological model. We present a new theoretical framework to analyze observations of stellar count and velocity in a self-consistent manner based on separable models, $f(E,J)=g(J)h(E)$, for the distribution function of an equilibrium spherical system. We use this machinery to analyze available photometric and kinematic data for the two stellar populations in Sculptor. We find, contrary to some previous claims, that the data are consistent with populations in equilibrium within an NFW dark matter potential with structural parameters in the range expected in ΛCDM; we find no statistical preference for a potential with a core. Our models allow a maximum circular velocity for Sculptor between 20 and 35 km s⁻¹. We discuss why some previous authors came to a different conclusion.

We observed the field of the Fermi source 3FGL J0838.8−2829 in optical and X-rays, initially motivated by the cataclysmic variable (CV) 1RXS J083842.1−282723 that lies within its error circle. Several X-ray sources first classified as CVs have turned out to be γ-ray emitting millisecond pulsars (MSPs). We find that 1RXS J083842.1−282723 is in fact an unusual CV, a stream-fed asynchronous polar in which accretion switches between magnetic poles (that are ≈120° apart) when the accretion rate is at minimum. High-amplitude X-ray modulation at periods of 94.8 ± 0.4 minutes and 14.7 ± 1.2 hr are seen. The former appears to be the spin period, while the latter is inferred to be one-third of the beat period between the spin and the orbit, implying an orbital period of 98.3 ± 0.5 minutes. We also measure an optical emission-line spectroscopic period of 98.413 ± 0.004 minutes, which is consistent with the orbital period inferred from the X-rays. In any case, this system is unlikely to be the γ-ray source. Instead, we find a fainter variable X-ray and optical source, XMMU J083850.38−282756.8, that is modulated on a timescale of hours in addition to exhibiting occasional sharp flares. It resembles the black widow or redback pulsars that have been discovered as counterparts of Fermi sources, with the optical modulation due to heating of the photosphere of a low-mass companion star by, in this case, an as-yet undetected MSP. We propose XMMU J083850.38−282756.8 as the MSP counterpart of 3FGL J0838.8−2829.

This paper examines the mechanism of internal shocks in opaque relativistic outflows, in particular in cosmological gamma-ray bursts. The shocks produce neutrino emission and affect the observed photospheric radiation from the explosion. They develop from internal compressive waves and can be of different types depending on the composition of the outflow. (1) Shocks in "photon gas," with negligible plasma inertia, have a unique structure determined by the force-free condition—zero radiation flux in the plasma rest frame. Radiation dominance over plasma inertia suppresses the formation of collisionless shocks mediated by collective electromagnetic fields. (2) If the outflow is sufficiently magnetized, a strong collisionless subshock develops, which is embedded in a thicker radiation-mediated structure. (3) Waves in outflows with a free neutron component lead to dissipation through nuclear collisions. At large optical depths, shocks have a thickness comparable to the neutron free path, with embedded radiation-mediated and collisionless subshocks. The paper also presents first-principles simulations of magnetized flows filled with photons, demonstrating the formation of shocks and their structure. Simple estimates show that magnetized sub-photospheric shocks are efficient producers of photons and have a great impact on the observed photospheric radiation. The shock structure changes as the outflow expands toward its photosphere. The dissipation is accompanied by strong ${e}^{\pm }$ pair creation, and the ${e}^{\pm }$-dressed shock carries the photosphere with it up to two decades in radius, emitting a strong pulse of nonthermal radiation.

The present work proposes a self-consistent reduced-order NLTE kinetic model for radiating plasmas found in the outer layers of stellar atmospheres. A detailed collisional-radiative kinetic mechanism is constructed by leveraging the most up-to-date set of ab initio and experimental data available in the literature. This constitutes the starting point for the derivation of a reduced-order model, obtained by lumping the bound energy states into groups. In order to determine the needed thermo-physical group properties, uniform and Maxwell–Boltzmann energy distributions are used to reconstruct the energy population of each group. Finally, the reduced set of governing equations for the material gas and the radiation field is obtained based on the moment method. Applications consider the steady flow across a shock wave in partially ionized hydrogen. The results clearly demonstrate that adopting a Maxwell–Boltzmann grouping allows, on the one hand, for a substantial reduction of the number of unknowns and, on the other, to maintain accuracy for both gas and radiation quantities. Also, it is observed that, when neglecting line radiation, the use of two groups already leads to a very accurate resolution of the photo-ionization precursor, internal relaxation, and radiative cooling regions. The inclusion of line radiation requires adopting just one additional group to account for optically thin losses in the α, β, and γ lines of the Balmer and Paschen series. This trend has been observed for a wide range of shock wave velocities.

We introduce the dense basis method for Spectral Energy Distribution (SED) fitting. It accurately recovers traditional SED parameters, including M_*, SFR, and dust attenuation, and reveals previously inaccessible information about the number and duration of star formation episodes and the timing of stellar mass assembly, as well as uncertainties in these quantities. This is done using basis star formation histories (SFHs) chosen by comparing the goodness-of-fit of mock galaxy SEDs to the goodness-of-reconstruction of their SFHs. We train and validate the method using a sample of realistic SFHs at z = 1 drawn from stochastic realizations, semi-analytic models, and a cosmological hydrodynamical galaxy formation simulation. The method is then applied to a sample of 1100 CANDELS GOODS-S galaxies at $1\lt z\lt 1.5$ to illustrate its capabilities at moderate S/N with 15 photometric bands. Of the six parametrizations of SFHs considered, we adopt linear-exponential, bessel-exponential, log-normal, and Gaussian SFHs, and reject the traditional parametrizations of constant (Top-Hat) and exponential SFHs. We quantify the bias and scatter of each parametrization. 15% of galaxies in our CANDELS sample exhibit multiple episodes of star formation, with this fraction decreasing above ${M}_{* }\gt {10}^{9.5}\,{M}_{\odot }$. About 40% of the CANDELS galaxies have SFHs whose maximum occurs at or near the epoch of observation. The dense basis method is scalable and offers a general approach to a broad class of data-science problems.

We investigate the nature of far-infrared (70 μm) and hard X-ray (3–24 keV) selected galaxies in the COSMOS field detected with both Spitzer and the Nuclear Spectroscopic Telescope Array (NuSTAR). By matching the Spitzer-COSMOS catalog with the NuSTAR-COSMOS catalog, we obtain a sample consisting of a hyperluminous infrared galaxy with $\mathrm{log}({L}_{\mathrm{IR}}/{L}_{\odot })\geqslant 13$, 12 ultraluminous infrared galaxies with $12\leqslant \mathrm{log}\,({L}_{\mathrm{IR}}/{L}_{\odot })\leqslant 13$, and 10 luminous infrared galaxies with $11\leqslant \mathrm{log}\,({L}_{\mathrm{IR}}/{L}_{\odot })\leqslant 12$, i.e., 23 Hy/U/LIRGs in total. Using their X-ray hardness ratios, we find that 12 sources are obscured active galactic nuclei (AGNs) with absorption column densities of ${N}_{{\rm{H}}}\gt {10}^{22}$ cm⁻², including several Compton-thick (${N}_{{\rm{H}}}\sim {10}^{24}$ cm⁻²) AGN candidates. On the basis of the infrared (60 μm) and intrinsic X-ray luminosities, we examine the relation between star formation (SF) and AGN luminosities of the 23 Hy/U/LIRGs. We find that the correlation is similar to that of the optically selected AGNs reported by Netzer, whereas local, far-infrared selected U/LIRGs show higher SF-to-AGN luminosity ratios than the average of our sample. This result suggests that our Hy/U/LIRGs detected both with Spitzer and NuSTAR are likely situated in a transition epoch between AGN-rising and cold-gas diminishing phases in SF-AGN evolutional sequences. The nature of a Compton-thick AGN candidate newly detected above 8 keV with NuSTAR (ID 245 in Civano et al.) is briefly discussed.

Galaxy mergers are likely to play a role in triggering active galactic nuclei (AGNs), but the conditions under which this process occurs are poorly understood. In Paper I, we constructed a sample of spatially offset X-ray AGNs that represent galaxy mergers hosting a single AGN. In this paper, we use our offset AGN sample to constrain the parameters that affect AGN observability in galaxy mergers. We also construct dual-AGN samples with similar selection properties for comparison. We find that the offset AGN fraction shows no evidence for a dependence on AGN luminosity, while the dual-AGN fractions show stronger evidence for a positive dependence, suggesting that the merger events forming dual AGNs are more efficient at instigating accretion onto supermassive black holes than those forming offset AGNs. We also find that the offset and dual-AGN fractions both have a negative dependence on nuclear separation and are similar in value at small physical scales. This dependence may become stronger when restricted to high AGN luminosities, although a larger sample is needed for confirmation. These results indicate that the probability of AGN triggering increases at later merger stages. This study is the first to systematically probe down to nuclear separations of <1 kpc (∼0.8 kpc) and is consistent with predictions from simulations that AGN observability peaks in this regime. We also find that the offset AGNs are not preferentially obscured compared to the parent AGN sample, suggesting that our selection may be targeting galaxy mergers with relatively dust-free nuclear regions.

The early part of a supernova (SN) light curve is dominated by radiation escaping from the expanding shock-heated progenitor envelope. For polytropic hydrogen envelopes, the properties of the emitted radiation are described by simple analytic expressions and are nearly independent of the polytropic index, n. This analytic description holds at early time, t < few days, during which radiation escapes from shells that are initially lying near the stellar surface. We use numerical solutions to address two issues. First, we show that the analytic description holds at early time also for nonpolytropic density profiles. Second, we extend the solutions to later times, when the emission emerges from deep within the envelope and depends on the progenitor's density profile. Examining the late time behavior of the polytropic envelopes with a wide range of core to envelope mass and radius ratios, 0.1 ≤ M_c/M_env ≤ 10 and 10⁻³ ≤ R_c/R ≤ 10⁻¹, we find that the effective temperature is well described by the analytic solution also at late time, while the luminosity, L, is suppressed by a factor, which may be approximated to be better than a 20 [30]% accuracy up to t = t_tr/a by $A\exp [-{({at}/{t}_{\mathrm{tr}})}^{\alpha }]$ with t_tr = 13 (M_env/M_⊙)^3/4(M/M_env)^1/4(E/10⁵¹erg)^−1/4 days, M = M_c + M_env, A = 0.9[0.8], a = 1.7[4.6], and α = 0.8[0.7] for n = 3/2[3]. This description holds as long as the opacity is approximately that of a fully ionized gas, i.e., for T > 0.7 eV, t < 14(R/10^13.5cm)^0.55 days. The suppression of L at t_tr/a that is obtained for standard polytropic envelopes may account for the first optical peak of double-peaked SN light curves, with the first peak at a few days for M_env < 1 M_⊙.

Using high spatial and temporal resolution Hα data from the New Vacuum Solar Telescope (NVST) and simultaneous observations from the Solar Dynamics Observatory, we present the rare event of the interaction between two filaments (F1 and F2) in AR 11967 on 2014 January 31. The adjacent two filaments were almost perpendicular to each other. Their interaction was driven by the movement of F1 and started when the two filaments collided with each other. During the interaction, the threads of F1 continuously slipped from the northeast to the southwest, and were accompanied by the brightenings at the junction of two filaments and the northeast footpoint of F2. Part of F1 and the main body of F2 became invisible in Hα wavelength due to the heating and the motion of F2. At the same time, bright material initiated from the junction of two filaments were observed to move along F1. The magnetic connectivities of F1 were found to be changed after their interaction. These observations suggest that magnetic reconnection was involved in the interaction of two filaments and resulted in the eruption of one filament.

Comparison analyses between the gas emission data (${\rm{H}}\,{\rm{I}}\,21\,\mathrm{cm}$ line and $\mathrm{CO}\,2.6\,\mathrm{mm}$ line) and the Planck/IRAS dust emission data (optical depth at $353\,\mathrm{GHz}\,{\tau }_{353}$ and dust temperature ${T}_{{\rm{d}}}$) allow us to estimate the amount and distribution of the hydrogen gas more accurately, and our previous studies revealed the existence of a large amount of optically thick ${\rm{H}}\,{\rm{I}}$ gas in the solar neighborhood. Referring to this, we discuss the neutral hydrogen gas around the Perseus cloud in the present paper. By using the J-band extinction data, we found that ${\tau }_{353}$ increases as a function of the 1.3th power of column number density of the total hydrogen (${N}_{{\rm{H}}}$), and this implies dust evolution in high density regions. This calibrated ${\tau }_{353}\mbox{--}{N}_{{\rm{H}}}$ relationship shows that the amount of the ${\rm{H}}\,{\rm{I}}$ gas can be underestimated to be $\sim 60 \%$ if the optically thin ${\rm{H}}\,{\rm{I}}$ method is used. Based on this relationship, we calculated the optical depth of the $21\,\mathrm{cm}$ line (${\tau }_{{\rm{H}}{\rm{I}}}$) and found that $\langle {\tau }_{{\rm{H}}{\rm{I}}}\rangle \sim 0.92$ around the molecular cloud. The effect of ${\tau }_{{\rm{H}}{\rm{I}}}$ is still significant, even if we take into account the dust evolution. We also estimated a spatial distribution of the $\mathrm{CO}$-to-${{\rm{H}}}_{2}$ conversion factor (${X}_{\mathrm{CO}}$), and we found its average value is $\langle {X}_{\mathrm{CO}}\rangle \sim 1.0\times {10}^{20}\,{\mathrm{cm}}^{-2}\,{{\rm{K}}}^{-1}\,{\mathrm{km}}^{-1}\,{\rm{s}}$. Although these results are inconsistent with some previous studies, these discrepancies can be well explained by the difference of the data and analyses methods.

We report the results of an XMM-Newton and NuSTAR coordinated observation of the Supergiant Fast X-ray Transient (SFXT) IGR J11215–5952, performed on 2016 February 14, during the expected peak of its brief outburst, which repeats every ∼165 days. Timing and spectral analysis were performed simultaneously in the energy band 0.4–78 keV. A spin period of 187.0 (±0.4) s was measured, consistent with previous observations performed in 2007. The X-ray intensity shows a large variability (more than one order of magnitude) on timescales longer than the spin period, with several luminous X-ray flares that repeat every 2–2.5 ks, some of which simultaneously observed by both satellites. The broadband (0.4–78 keV) time-averaged spectrum was well deconvolved with a double-component model (a blackbody plus a power law with a high energy cutoff) together with a weak iron line in emission at 6.4 keV (equivalent width, EW, of 40 ± 10 eV). Alternatively, a partial covering model also resulted in an adequate description of the data. The source time-averaged X-ray luminosity was 10³⁶ erg s⁻¹ (0.1–100 keV; assuming 7 kpc). We discuss the results of these observations in the framework of the different models proposed to explain SFXTs, supporting a quasi-spherical settling accretion regime, although alternative possibilities (e.g., centrifugal barrier) cannot be ruled out.

The solar magnetic field in a flare-producing active region (AR) is much more complicated than theoretical models, which assume a very simple magnetic field structure. The X1.0 flare, which occurred in AR 12192 on 2014 October 25, showed a complicated three-ribbon structure. To clarify the trigger process of the flare and to evaluate the applicability of a simple theoretical model, we analyzed the data from Hinode/Solar Optical Telescope and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Atmospheric Imaging Assembly. We investigated the spatio-temporal correlation between the magnetic field structures, especially the non-potentiality of the horizontal field, and the bright structures in the solar atmosphere. As a result, we determined that the western side of the positive polarity, which is intruding on a negative polarity region, is the location where the flare was triggered. This is due to the fact that the sign of the magnetic shear in that region was opposite that of the major shear of the AR, and the significant brightenings were observed over the polarity inversion line (PIL) in that region before flare onset. These features are consistent with the recently proposed flare-trigger model that suggests that small reversed shear (RS) magnetic disturbances can trigger solar flares. Moreover, we found that the RS field was located slightly off the flaring PIL, contrary to the theoretical prediction. We discuss the possibility of an extension of the RS model based on an extra numerical simulation. Our result suggests that the RS field has a certain flexibility for displacement from a highly sheared PIL, and that the RS field triggers more flares than we expected.

Very few low-ionization broad absorption line (LoBAL) QSOs have been found at high redshifts, to date. One high-redshift LoBAL QSO, J0122+1216, was recently discovered by the Lijiang 2.4 m Telescope, with an initial redshift determination of 4.76. Aiming to investigate its physical properties, we carried out follow-up observations in the optical and near-IR spectroscopy. Near-IR spectra from UKIRT and P200 confirm that it is a LoBAL, with a new redshift determination of 4.82 ± 0.01 based on the Mg ii emission-line. The new Mg ii redshift determination reveals strong blueshifts and asymmetry of the high-ionization emission lines. We estimate a black hole mass of ∼2.3 × 10⁹M_⊙ and Eddington ratio of ∼1.0 according to the empirical Mg ii-based single-epoch relation and bolometric correction factor. It is possible that strong outflows are the result of an extreme quasar environment driven by the high Eddington ratio. A lower limit on the outflowing kinetic power (>0.9% L_Edd) is derived from both emission and absorption lines, indicating that these outflows play a significant role in the feedback process that regulates the growth of its black hole, as well as host galaxy evolution.

We report observations of dense molecular gas in the star-forming galaxy EGS 13004291 (z = 1.197) using the Plateau de Bure Interferometer. We tentatively detect HCN and HNC $J=2\to 1$ emission when stacked together at $4\sigma$ significance, yielding line luminosities of ${L}_{\mathrm{HCN}(J=2\to 1)}^{\prime }=(9\pm 3)\times {10}^{9}$ K km s⁻¹ pc² and ${L}_{\mathrm{HNC}(J=2\to 1)}^{\prime }=(5\pm 2)\times {10}^{9}$ K km s⁻¹ pc², respectively. We also set 3σ upper limits of <7–8 ×10⁹ K km s⁻¹ pc² on the ${\mathrm{HCO}}^{+}(J=2\to 1)$, ${{\rm{H}}}_{2}{\rm{O}}({3}_{13}\to {2}_{20}$), and HC₃N(J = 20 → 19) line luminosities. We serendipitously detect CO emission from two sources at $z\sim 1.8$ and $z\sim 3.2$ in the same field of view. We also detect CO($J=2\to 1$) emission in EGS 13004291, showing that the excitation in the previously detected CO($J=3\to 2$) line is subthermal (${r}_{32}=0.65\pm 0.15$). We find a line luminosity ratio of ${L}_{\mathrm{HCN}}^{\prime }$/${L}_{\mathrm{CO}}^{\prime }$ = 0.17 ± 0.07, as an indicator of the dense gas fraction. This is consistent with the median ratio observed in $z\gt 1$ galaxies (${L}_{\mathrm{HCN}}^{\prime }$/${L}_{\mathrm{CO}}^{\prime }$ = 0.16 ± 0.07) and nearby ULIRGs (${L}_{\mathrm{HCN}}^{\prime }$/${L}_{\mathrm{CO}}^{\prime }$ = 0.13 ± 0.03), but higher than that in local spirals (${L}_{\mathrm{HCN}}^{\prime }$/${L}_{\mathrm{CO}}^{\prime }$ = 0.04 ± 0.02). Although EGS 13004291 lies significantly above the galaxy main sequence at $z\sim 1$, we do not find an elevated star formation efficiency (traced by ${L}_{\mathrm{FIR}}$/${L}_{\mathrm{CO}}^{\prime }$) as in local starbursts, but a value consistent with main-sequence galaxies. The enhanced dense gas fraction, the subthermal gas excitation, and the lower than expected star formation efficiency of the dense molecular gas in EGS 13004291 suggest that different star formation properties may prevail in high-z starbursts. Thus, using ${L}_{\mathrm{FIR}}$/${L}_{\mathrm{CO}}^{\prime }$ as a simple recipe to measure the star formation efficiency may be insufficient to describe the underlying mechanisms in dense star-forming environments inside the large gas reservoirs.

We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z > 4 and the strong lensing model (μ = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 10¹⁰L_⊙ and an obscured star formation rate of 14.6 ± 4.5 M_⊙ yr⁻¹. The unobscured star formation rate from the UV is only 4.1 ± 0.3 M_⊙ yr⁻¹, which means the total star formation rate (18.7 ± 4.5 M_⊙ yr⁻¹) is dominated (75%–80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 10⁹M_⊙, MACS0717_Az9 is one of only a handful of z > 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe.

We consider the observational basis for the belief that flare ribbons in the chromosphere result from energy transport from the overlying corona. We study ribbons of small flares using magnetic and intensity data from the Hinode, Solar Dynamics Observatory, and IRIS missions. While most ribbons appear connected to the corona and overlie regions of significant vertical magnetic field, we examine one ribbon with no clear evidence for such connections. Evolving horizontal magnetic fields seen with Hinode suggest that reconnection with preexisting fields below the corona can explain the data. The identification of just one, albeit small, ribbon, with no apparent connection to the corona, leads us to conclude that at least two mechanisms are responsible for the heating that leads to flare ribbon emission.

The third Fermi Large Area Telescope γ-ray source catalog (3FGL) contains over 1000 objects for which there is no known counterpart at other wavelengths. The physical origin of the γ-ray emission from those objects is unknown. Such objects are commonly referred to as unassociated and mostly do not exhibit significant γ-ray flux variability. We performed a survey of all unassociated γ-ray sources found in 3FGL using the Australia Telescope Compact Array and Very Large Array in the range 4.0–10.0 GHz. We found 2097 radio candidates for association with γ-ray sources. The follow-up with very long baseline interferometry for a subset of those candidates yielded 142 new associations with active galactic nuclei that are γ-ray sources, provided alternative associations for seven objects, and improved positions for another 144 known associations to the milliarcsecond level of accuracy. In addition, for 245 unassociated γ-ray sources we did not find a single compact radio source above 2 mJy within 3σ of their γ-ray localization. A significant fraction of these empty fields, 39%, are located away from the Galactic plane. We also found 36 extended radio sources that are candidates for association with a corresponding γ-ray object, 19 of which are most likely supernova remnants or H ii regions, whereas 17 could be radio galaxies.

Observational studies of the magnetic fields in molecular clouds have significantly improved the theoretical models developed for the structure and evolution of dense clouds and for the star formation process as well. The recent observational analyses on some cores indicate that there is a power-law relationship between magnetic field and density in the molecular clouds. In this study, we consider the stability of spherical cores with a toroidal magnetic field configuration in the molecular clouds. For this purpose, we model a spherical core that is in magnetostatic equilibrium. Herein, we propose an equation of density structure, which is a modified form of the isothermal Lane–Emden equation in the presence of the toroidal magnetic field. The proposed equation describes the effect of the toroidal magnetic field on the cloud structure and the mass cloud. Furthermore, we found an upper limit for this configuration of magnetic field in the molecular clouds. Then, the virial theorem is used to consider the cloud evolution leading to an equation in order to obtain the lower limit of the field strength in the molecular cloud. However, the results show that the field strength of the toroidal configuration has an important effect on the cloud structure, whose upper limit is related to the central density and field gradient. The obtained results address some regions of clouds where the cloud decomposition or star formation can be seen.

We present the first multi-viewpoint coronal mass ejection (CME) catalog. The events are identified visually in simultaneous total brightness observations from the twin SECCHI/COR2 coronagraphs on board the Solar Terrestrial Relations Observatory mission. The Multi-View CME Catalog differs from past catalogs in three key aspects: (1) all events between the two viewpoints are cross-linked, (2) each event is assigned a physics-motivated morphological classification (e.g., jet, wave, and flux rope), and (3) kinematic and geometric information is extracted semi-automatically via a supervised image segmentation algorithm. The database extends from the beginning of the COR2 synoptic program (2007 March) to the end of dual-viewpoint observations (2014 September). It contains 4473 unique events with 3358 events identified in both COR2s. Kinematic properties exist currently for 1747 events (26% of COR2-A events and 17% of COR2-B events). We examine several issues, made possible by this cross-linked CME database, including the role of projection on the perceived morphology of events, the missing CME rate, the existence of cool material in CMEs, the solar cycle dependence on CME rate, speeds and width, and the existence of flux rope within CMEs. We discuss the implications for past single-viewpoint studies and for Space Weather research. The database is publicly available on the web including all available measurements. We hope that it will become a useful resource for the community.

The observed radial profiles of the X-ray emission from pulsar wind nebulae (PWNe) have been claimed to contradict the standard 1D steady model. However, the 1D model has not been tested to simultaneously reproduce the volume-integrated spectrum and the radial profile of the surface brightness. We revisit the 1D steady model and apply it to PWNe 3C 58 and G21.5−0.9. We find that the parameters of the pulsar wind, the radius of the termination shock ${r}_{{\rm{s}}}$, and magnetization σ greatly affect both the photon spectrum and radial profile of the emission. We have shown that the parameters constrained by the entire spectrum lead to an X-ray nebula smaller than the observed nebula. We have also tested the case that reproduces only the observations in X- and gamma-rays, ignoring the radio and optical components. In this case, there are parameter sets that reproduce both the spectrum and emission profile, but the advection time to the edge of the nebula becomes much smaller than the age. Our detailed discussion clarifies that the standard 1D steady model has severe difficulty to simultaneously reproduce both the volume-integrated spectrum and the surface brightness. This implies that the model should be improved by taking into account extra physical processes such as spatial diffusion of particles. Additionally, we calculate the surface brightness profile of the radio, optical, and TeV gamma-rays. The future observations in these wavelengths are also important to probe the spatial distributions of the relativistic plasma and the magnetic field of PWNe.

Recently, two empirical correlations related to the minimum variability timescale (MTS) of the light curves are discovered in gamma-ray bursts (GRBs). One is the anti-correlation between MTS and Lorentz factor Γ, and the other is the anti-correlation between the MTS and gamma-ray luminosity L_γ. Both of the two correlations might be used to explore the activity of the central engine of GRBs. In this paper, we try to understand these empirical correlations by combining two popular black hole central engine models (namely, the Blandford & Znajek mechanism (BZ) and the neutrino-dominated accretion flow (NDAF)). By taking the MTS as the timescale of viscous instability of the NDAF, we find that these correlations favor the scenario in which the jet is driven by the BZ mechanism.

We present measurements of the singly ionized helium-to-hydrogen ratio (${n}_{{\mathrm{He}}^{+}}/{n}_{{{\rm{H}}}^{+}}$) toward diffuse gas surrounding three ultracompact H ii (UCH ii) regions: G10.15-0.34, G23.46-0.20, and G29.96-0.02. We observe radio recombination lines of hydrogen and helium near 5 GHz using the GBT to measure the ${n}_{{\mathrm{He}}^{+}}/{n}_{{{\rm{H}}}^{+}}$ ratio. The measurements are motivated by the low helium ionization observed in the warm ionized medium and in the inner Galaxy diffuse ionized regions. Our data indicate that the helium is not uniformly ionized in the three observed sources. Helium lines are not detected toward a few observed positions in sources G10.15-0.34 and G23.46-0.20, and the upper limits of the ${n}_{{\mathrm{He}}^{+}}/{n}_{{{\rm{H}}}^{+}}$ ratio obtained are 0.03 and 0.05, respectively. The selected sources harbor stars of type O6 or hotter as indicated by helium line detection toward the bright radio continuum emission from the sources with mean ${n}_{{\mathrm{He}}^{+}}/{n}_{{{\rm{H}}}^{+}}$ value 0.06 ± 0.02. Our data thus show that helium in diffuse gas located a few parsecs away from the young massive stars embedded in the observed regions is not fully ionized. We investigate the origin of the nonuniform helium ionization and rule out the possibilities (a) that the helium is doubly ionized in the observed regions and (b) that the low ${n}_{{\mathrm{He}}^{+}}/{n}_{{{\rm{H}}}^{+}}$ values are due to additional hydrogen ionizing radiation produced by accreting low-mass stars. We find that selective absorption of ionizing photons by dust can result in low helium ionization but needs further investigation to develop a self-consistent model for dust in H ii regions.

We present broadband spectral energy distributions and light curves of the gamma-ray binary 1FGL J1018.6−5856 measured in the X-ray and the gamma-ray bands. We find that the orbital modulation in the low-energy gamma-ray band is similar to that in the X-ray band, suggesting a common spectral component. However, above a GeV the orbital light curve changes significantly. We suggest that the GeV band contains significant flux from a pulsar magnetosphere, while the X-ray to TeV light curves are dominated by synchrotron and Compton emission from an intrabinary shock (IBS). We find that a simple one-zone model is inadequate to explain the IBS emission, but that beamed Synchrotron-self Compton radiation from adiabatically accelerated plasma in the shocked pulsar wind can reproduce the complex multiband light curves, including the variable X-ray spike coincident with the gamma-ray maximum. The model requires an inclination of ∼50° and an orbital eccentricity of ∼0.35, consistent with the limited constraints from existing optical observations. This picture motivates searches for pulsations from the energetic young pulsar powering the wind shock.

We use the Atacama Large Millimeter Array (ALMA) to detect and image CO (1-0) emission from Minkowski's Object, a dwarf galaxy in the cluster Abell 194 that is interacting with a radio jet from a nearby elliptical galaxy. The ALMA observations, which are the first to detect molecular gas in Minkowski's Object, also image the high-frequency continuum emission from the radio jet, allowing us to study the interaction in detail. We estimate the range in the mass of molecular gas in Minkowski's Object assuming two different values of the ratio of the molecular gas mass to the CO luminosity, ${\alpha }_{\mathrm{CO}}$. For the Milky Way value of ${\alpha }_{\mathrm{CO}}=4.6\,{M}_{\odot }{({\rm{K}}\mathrm{km}{{\rm{s}}}^{-1}{\mathrm{pc}}^{2})}^{-1}$ we obtain a molecular gas mass of ${M}_{{{\rm{H}}}_{2}}=3.0\times {10}^{7}\,{M}_{\odot }$, 6% of the H I gas mass. We also use the prescription of Narayanan et al. (2012) to estimate an ${\alpha }_{\mathrm{CO}}=27\,{M}_{\odot }{({\rm{K}}\mathrm{km}{{\rm{s}}}^{-1}{\mathrm{pc}}^{2})}^{-1}$, in which case we obtain ${M}_{{{\rm{H}}}_{2}}=1.8\times {10}^{8}\,{M}_{\odot }$, 36% of the H I mass. The observations are consistent with previous claims of star formation being induced in Minkowski's Object via the passage of the radio jet, and it therefore being a rare local example of positive feedback from an active galactic nucleus. In particular, we find highly efficient star formation, with gas depletion timescales $\sim 5\times {10}^{7}\mbox{--}3\times {10}^{8}$ year (for assumed values of ${\alpha }_{\mathrm{CO}}=4.6$ and $27\,{M}_{\odot }{({\rm{K}}\mathrm{km}{{\rm{s}}}^{-1}{\mathrm{pc}}^{2})}^{-1}$, respectively) in the upstream regions of Minkowski's Object that were struck first by the jet, and less efficient star formation downstream. We discuss the implications of this observation for models of jet-induced star formation and radio-mode feedback in massive galaxies.

Observations of the sungrazing comet C/2012 S1 (ISON) were carried out using the Atacama Large Millimeter/submillimeter Array at a heliocentric distance of 0.58–0.54 au (pre-perihelion) on 2013 November 16–17. Temporally resolved measurements of the coma distributions of HNC, CH₃OH, H₂CO, and dust were obtained over the course of about an hour on each day. During the period UT 10:10–11:00 on November 16, the comet displayed a remarkable drop in activity, manifested as a >42% decline in the molecular line and continuum fluxes. The H₂CO observations are consistent with an abrupt, ≈50% reduction in the cometary gas production rate soon after the start of our observations. On November 17, the total observed fluxes remained relatively constant during a similar period, but strong variations in the morphology of the HNC distribution were detected as a function of time, indicative of a clumpy, intermittent outflow for this species. Our observations suggest that at least part of the detected HNC originated from degradation of nitrogen-rich organic refractory material, released intermittently from confined regions of the nucleus. By contrast, the distributions of CH₃OH and H₂CO during the November 17 observations were relatively uniform, consistent with isotropic outflow and stable activity levels for these species. These results highlight a large degree of variability in the production of gas and dust from comet ISON during its pre-perihelion outburst, consistent with repeated disruption of the nucleus interspersed with periods of relative quiescence.

Galaxies that abruptly interrupt their star formation in $\lt 1.5\,\mathrm{Gyr}$ present recognizable features in their spectra (no emission and Hδ in absorption) and are called post-starburst (PSB) galaxies. By studying their stellar population properties and their location within the clusters, we obtain valuable insights on the physical processes responsible for star formation quenching. We present the first complete characterization of PSB galaxies in clusters at $0.04\lt z\lt 0.07$, based on WINGS and OmegaWINGS data, and contrast their properties to those of passive (PAS) and emission-line (EML) galaxies. For $V\lt 20$, PSBs represent 7.2 ± 0.2% of cluster galaxies within 1.2 virial radii. Their incidence slightly increases from the outskirts toward the cluster center and from the least toward the most luminous and massive clusters, defined in terms of X-ray luminosity and velocity dispersion. The phase-space analysis and velocity-dispersion profile suggest that PSBs represent a combination of galaxies with different accretion histories. Moreover, PSBs with the strongest Hδ are consistent with being recently accreted. PSBs have stellar masses, magnitudes, colors, and morphologies intermediate between PAS and EML galaxies, typical of a population in transition from being star-forming to passive. Comparing the fraction of PSBs to the fraction of galaxies in transition on longer timescales, we estimate that the short-timescale star formation quenching channel contributes two times more than the long timescale one to the growth of the passive population. Processes like ram-pressure stripping and galaxy–galaxy interactions are more efficient than strangulation in affecting star formation.

We perform a comprehensive study of the X-ray emission from 70 transient sources that have been classified as tidal disruption events (TDEs) in the literature. We explore the properties of these candidates, using nearly three decades of X-ray observations to quantify their properties and characteristics. We find that the emission from X-ray TDEs increase by two to three orders of magnitude, compared to pre-flare constraints. These emissions evolve significantly with time, and decay with power-law indices that are typically shallower than the canonical t^−5/3 decay law, implying that X-ray TDEs are viscously delayed. These events exhibit enhanced (relative to galactic) column densities and are quite soft in nature, with no strong correlation between the amount of detected soft and hard emission. At their peak, jetted events have an X-ray to optical ratio ≫1, whereas non-jetted events have a ratio ∼1, which suggests that these events undergo reprocessing at different rates. X-ray TDEs have long T₉₀ values, consistent with what would be expected from a viscously driven accretion disk formed by the disruption of a main-sequence star by a black hole with a mass <10⁷M_⊙. The isotropic luminosities of X-ray TDEs are bimodal, such that jetted and non-jetted events are separated by a "reprocessing valley" that we suggest is naturally populated by optical/UV TDEs that most likely produce X-rays, but this emission is "veiled" from observations due to reprocessing. Our results suggest that non-jetted X-ray TDEs likely originate from partial disruptions and/or disruptions of low-mass stars.

The census of Taurus–Auriga has been assembled over seven decades and inherited the biases and incompleteness of the input studies. The unusual shape of its inferred initial mass function (IMF) and the existence of isolated disk-bearing stars suggest that additional (likely disk-free) members remain to be discovered. We therefore have begun a global reassessment of the census of Taurus–Auriga that exploits new data and better definitions of youth and kinematic membership. As a first step, we reconsider the membership of all disk-free candidate members from the literature with spectral type ≥F0, ${3}^{{\rm{h}}}{50}^{{\rm{m}}}\lt \alpha \lt {5}^{{\rm{h}}}{40}^{{\rm{m}}}$, and $14^\circ \lt \delta \lt 34^\circ$. We combine data from the literature with Keck/HIRES and UH88/SNIFS spectra to test the membership of these candidates using the positions in the Hertzsprung-Russel diagram, proper motions, radial velocities, Hα, lithium, and surface gravity. We find 218 confirmed or likely Taurus members, 160 confirmed or likely interlopers, and only 18 that lack sufficient evidence to draw firm conclusions. A significant fraction of these stars (81/218 = 37%) are not included in the most recent canonical member lists. There are few additional members to the immediate vicinity of the molecular clouds, preserving the IMFs that have been deemed anomalous in past work. Many of the likely Taurus members are instead distributed broadly across the search area. When combined with the known disk hosts, our updated census reveals two regimes: a high-density population with a high disk fraction (indicative of youth) that broadly traces the molecular clouds, and a low-density population with low disk fraction (hence likely older) that most likely represents previous generations of star formation.

We investigate the dust structure of gravitationally unstable disks undergoing mass accretion from the envelope, envisioning its application to Class 0/I young stellar objects (YSOs). We find that the dust disk quickly settles into a steady state and that, compared to a disk with interstellar medium (ISM) dust-to-gas mass ratio and micron-sized dust, the dust mass in the steady state decreases by a factor of 1/2 to 1/3, and the dust thermal emission decreases by a factor of 1/3 to 1/5. The latter decrease is caused by dust depletion and opacity decrease owing to dust growth. Our results suggest that the masses of gravitationally unstable disks in Class 0/I YSOs are underestimated by a factor of 1/3 to 1/5 when calculated from the dust thermal emission assuming an ISM dust-to-gas mass ratio and micron-sized dust opacity, and that a larger fraction of disks in Class 0/I YSOs is gravitationally unstable than was previously believed. We also investigate the orbital radius ${r}_{{\rm{P}}}$ within which planetesimals form via coagulation of porous dust aggregates and show that ${r}_{{\rm{P}}}$ becomes ∼20 au for a gravitationally unstable disk around a solar mass star. Because ${r}_{{\rm{P}}}$ increases as the gas surface density increases and a gravitationally unstable disk has maximum gas surface density, ${r}_{{\rm{P}}}\sim 20\,\mathrm{au}$ is the theoretical maximum radius for planetesimal formation. We suggest that planetesimal formation in the Class 0/I phase is preferable to that in the Class II phase because a large amount of dust is supplied by envelope-to-disk accretion.

We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at the McDonald Observatory. IGRINS has high spectral resolution ($R\sim {\rm{45,000}}$) and instantaneous broad wavelength coverage (1.45–2.45 μm), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H₂) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H₂ and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments ($T=50\mbox{--}250$ K, ${n}_{H}={10}^{5}\mbox{--}{10}^{7}$ cm⁻³) embedded in a warmer lower density medium ($T=250\mbox{--}1000$ K, ${n}_{H}={10}^{4}\mbox{--}{10}^{5}$ cm⁻³). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H₂ level populations well, to constrain the temperature to a range of 600–650 K and the density to ${n}_{H}=2.5\times {10}^{3}\mbox{--}{10}^{4}$ cm⁻³. The best-fit model gives T = 625 K and ${n}_{H}=5\times {10}^{3}$ cm⁻³. This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar's lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.

An unexpectedly slow evolution in the pre-optical-maximum phase was suggested in the very short recurrence period of nova M31N 2008-12a. To obtain reasonable nova light curves we have improved our calculation method by consistently combining optically thick wind solutions of hydrogen-rich envelopes with white dwarf (WD) structures calculated by a Henyey-type evolution code. The wind mass-loss rate is properly determined with high accuracy. We have calculated light curve models for 1.2 M_⊙ and 1.38 M_⊙ WDs with mass accretion rates corresponding to recurrence periods of 10 yr and 1 yr, respectively. The outburst lasts 590/29 days, in which the pre-optical-maximum phase is 82/16 days, for 1.2/1.38 M_⊙, respectively. Optically thick winds start at the end of the X-ray flash and cease at the beginning of the supersoft X-ray phase. We also present supersoft X-ray light curves including a prompt X-ray flash and later supersoft X-ray phase.

We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from Spitzer. The Spitzer data exhibit finite-source effects that are due to the passage of the lens close to or directly over the surface of the source star as seen from Spitzer. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the Spitzer light curves yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with a mass $0.10\pm 0.02\ {M}_{\odot }$ or a brown dwarf with a mass $55\pm 9\ {M}_{J}$, which are located at ${D}_{\mathrm{LS}}=0.80\pm 0.19\ \mathrm{kpc}$ and ${D}_{\mathrm{LS}}=0.54\pm 0.08\ \mathrm{kpc}$, respectively, where ${D}_{\mathrm{LS}}$ is the distance between the lens and the source, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The degeneracy between the two solutions is severe (${\rm{\Delta }}{\chi }^{2}=0.3$). The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from Spitzer, and this single data point gives rise to two solutions for ρ, the angular size of the source in units of the angular Einstein ring radius. Because the ρ degeneracy can be resolved only by relatively high-cadence observations around the peak, while the Spitzer cadence is typically $\sim 1\,{\mathrm{day}}^{-1}$, we expect that events for which the finite-source effect is seen only in the Spitzer data may frequently exhibit this ρ degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is ${\mu }_{\mathrm{rel}}=9.0\pm 1.9\ \mathrm{mas}\,{\mathrm{yr}}^{-1}$, while for the brown dwarf it is $5.5\pm 0.5\ \mathrm{mas}\,{\mathrm{yr}}^{-1}$. Hence, the degeneracy can be resolved within $\sim 10\ \mathrm{years}$ from direct-lens imaging by using next-generation instruments with high spatial resolution.

I present a family of algorithms to reduce noise in astrophysical images and image sequences, preserving more information from the original data than is retained by conventional techniques. The family uses locally adaptive filters ("noise gates") in the Fourier domain to separate coherent image structure from background noise based on the statistics of local neighborhoods in the image. Processing of solar data limited by simple shot noise or by additive noise reveals image structure not easily visible in the originals, preserves photometry of observable features, and reduces shot noise by a factor of 10 or more with little to no apparent loss of resolution. This reveals faint features that were either not directly discernible or not sufficiently strongly detected for quantitative analysis. The method works best on image sequences containing related subjects, for example movies of solar evolution, but is also applicable to single images provided that there are enough pixels. The adaptive filter uses the statistical properties of noise and of local neighborhoods in the data to discriminate between coherent features and incoherent noise without reference to the specific shape or evolution of those features. The technique can potentially be modified in a straightforward way to exploit additional a priori knowledge about the functional form of the noise.

We report on a timing and spectral analysis of the young, high magnetic field rotation-powered pulsar (RPP) B1509−58 using Chandra continuous-clocking mode observation. The pulsar's X-ray light curve can be fit by the two Gaussian components and the pulsed fraction shows moderate energy dependence over the Chandra band. The pulsed X-ray spectrum is well described by a power law with a photon index 1.16(4), which is harder than the values measured with RXTE/PCA and NuSTAR. This result supports the log-parabolic model for the broadband X-ray spectrum. With the unprecedented angular resolution of Chandra, we clearly identified off-pulse X-ray emission from the pulsar, and its spectrum is best fit by a power law plus blackbody model. The latter component has a temperature of ∼0.14 keV with a bolometric luminosity comparable to the luminosities of other young and high magnetic field RPPs, and it lies between the temperature of magnetars and typical RPPs. In addition, we found that the nonthermal X-ray emission of PSR B1509−58 is significantly softer in the off-pulse phase than in the pulsed phase, with the photon index varying between 1.0 and 1.8 and anticorrelated with the flux. This is similar to the behavior of three other young pulsars. We interpreted it as different contributions of pair-creation processes at different altitudes from the neutron star surface according to the outer-gap model.

A close-in giant planetary (CGP) system has a net polarization signal whose value varies depending on the orbital phase of the planet. This polarization signal is either caused by the stellar occultation or by reflected starlight from the surface of the orbiting planet. When the CGP system is located in the Galactic bulge, its polarization signal becomes too weak to be measured directly. One method for detecting and characterizing these weak polarization signatures due to distant CGP systems is gravitational microlensing. In this work, we focus on potential polarimetric observations of highly magnified microlensing events of CGP systems. When the lens is passing directly in front of the source star with its planetary companion, the polarimetric signature caused by the transiting planet is magnified. As a result, some distinct features in the polarimetry and light curves are produced. In the same way, microlensing amplifies the reflection-induced polarization signal. While the planet-induced perturbations are magnified whenever these polarimetric or photometric deviations vanish for a moment, the corresponding magnification factor of the polarization component(s) is related to the planet itself. Finding these exact times in the planet-induced perturbations helps us to characterize the planet. In order to evaluate the observability of such systems through polarimetric or photometric observations of high-magnification microlensing events, we simulate these events by considering confirmed CGP systems as their source stars and conclude that the efficiency for detecting the planet-induced signal with the state-of-the-art polarimetric instrument (FORS2/VLT) is less than 0.1%. Consequently, these planet-induced polarimetry perturbations can likely be detected under favorable conditions by the high-resolution and short-cadence polarimeters of the next generation.

The relationship between a decaying strong turbulence and the mirror instability in a slowly expanding plasma is investigated using two-dimensional hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and a vanishing correlation between the two fields. A turbulent cascade rapidly develops, magnetic field fluctuations exhibit a Kolmogorov-like power-law spectrum at large scales and a steeper spectrum at sub-ion scales. The imposed expansion (taking a strictly transverse ambient magnetic field) leads to the generation of an important perpendicular proton temperature anisotropy that eventually drives the mirror instability. This instability generates large-amplitude, nonpropagating, compressible, pressure-balanced magnetic structures in a form of magnetic enhancements/humps that reduce the perpendicular temperature anisotropy.

We investigate the integrated properties of massive ($\gt 10\,{M}_{\odot }$) rotating single-star stellar populations for a variety of initial rotation rates ($v/{v}_{\mathrm{crit}}=0.0$, 0.2, 0.4, 0.5, and 0.6). We couple the new MESA Isochrone and Stellar Tracks (MIST) models to the Flexible Stellar Population Synthesis (FSPS) package, extending the stellar population synthesis models to include the contributions from very massive stars ($\gt 100\,{M}_{\odot }$), which can be significant in the first ∼4 Myr after a starburst. These models predict ionizing luminosities that are consistent with recent observations of young nuclear star clusters. We also construct composite stellar populations assuming a distribution of initial rotation rates. Even in low-metallicity environments where rotation has a significant effect on the evolution of massive stars, we find that stellar population models require a significant contribution from fast-rotating ($v/{v}_{\mathrm{crit}}\gt 0.4$) stars in order to sustain the production of ionizing photons beyond a few Myr following a starburst. These results have potentially important implications for cosmic reionization by massive stars and the interpretation of nebular emission lines in high-redshift star-forming galaxies.

In this paper, we propose an improved model-independent method to constrain the cosmic curvature by combining the most recent Hubble parameter H(z) and supernovae Ia (SNe Ia) data. Based on the H(z) data, we first use the model-independent smoothing technique, Gaussian processes, to construct a distance modulus μ_H(z), which is susceptible to the cosmic curvature parameter Ω_k. In contrary to previous studies, the light-curve-fitting parameters, which account for the distance estimation of SN (μ_SN(z)), are set free to investigate whether Ω_k has a dependence on them. By comparing μ_H(z) to μ_SN(z), we put limits on Ω_k. Our results confirm that Ω_k is independent of the SN light-curve parameters. Moreover, we show that the measured Ω_k is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat universe at the current observational data level. We also test the influence of different H(z) samples and different Hubble constant H₀ values, finding that different H(z) samples do not have a significant impact on the constraints. However, different H₀ priors can affect the constraints of Ω_k to some degree. The prior of H₀ = 73.24 ± 1.74 km s⁻¹ Mpc⁻¹ gives a value of Ω_k, a little bit above the 1σ confidence level away from 0, but H₀ = 69.6 ± 0.7 km s⁻¹ Mpc⁻¹ gives it below 1σ.

We introduce the Yale–Potsdam Stellar Isochrones (YaPSI), a new grid of stellar evolution tracks and isochrones of solar-scaled composition. In an effort to improve the Yonsei–Yale database, special emphasis is placed on the construction of accurate low-mass models (${M}_{* }\lt 0.6\,{M}_{\odot }$), and in particular on their mass–luminosity and mass–radius relations, both crucial for characterizing exoplanet-host stars, and, in turn, their planetary systems. The YaPSI models cover the mass range 0.15–$5.0\,{M}_{\odot }$ densely enough to permit detailed interpolation in mass, and the metallicity and helium abundance ranges [Fe/H] = −1.5 to +0.3 and Y₀ = 0.25–0.37 are specified independently of each other (i.e., no fixed ${\rm{\Delta }}Y/{\rm{\Delta }}Z$ relation is assumed). The evolutionary tracks are calculated from the pre-main sequence up to the tip of the red giant branch. The isochrones, with ages between 1 Myr and 20 Gyr, provide UBVRI colors in the Johnson–Cousins system, and JHK colors in the homogenized Bessell & Brett system, derived from two different semi-empirical ${T}_{\mathrm{eff}}$–color calibrations from the literature. We also provide utility codes, such as an isochrone interpolator, in age, metallicity, and helium content, and an interface of the tracks with an open-source Monte Carlo Markov-Chain tool for the analysis of individual stars. Finally, we present comparisons of the YaPSI models with the best empirical mass–luminosity and mass–radius relations available to date, as well as isochrone fitting of well-studied stellar clusters.

The recent Gaia Data Release 1 of stellar parallaxes provides ample opportunity to find metal-poor main-sequence stars with precise parallaxes. We select 21 such stars with parallax uncertainties better than σ_π/π ≤ 0.10 and accurate abundance determinations suitable for testing metal-poor stellar evolution models and determining the distance to Galactic globular clusters (GCs). A Monte Carlo analysis was used, taking into account uncertainties in the model construction parameters, to generate stellar models and isochrones to fit to the calibration stars. The isochrones that fit the calibration stars best were then used to determine the distances and ages of 22 GCs with metallicities ranging from −2.4 dex to −0.7 dex. We find distances with an average uncertainty of 0.15 mag and absolute ages ranging from 10.8 to 13.6 Gyr with an average uncertainty of 1.6 Gyr. Using literature proper motion data, we calculate orbits for the clusters, finding six that reside within the Galactic disk/bulge, while the rest are considered halo clusters. We find no strong evidence for a relationship between age and Galactocentric distance, but we do find a decreasing age–[Fe/H] relation.

We provide an explanation of the properties of the fundamental plane (FP) relation and its observed projections for a sample of nearby early-type galaxies (ETGs) in terms of a fine-tuning between the time-averaged star formation rate $\langle {\rm{\Psi }}\rangle$ and their structural and dynamical characteristics. Their total V luminosity is linked with $\langle {\rm{\Psi }}\rangle$ and the central velocity dispersion σ through the relation $\mathrm{log}(L)=0.48(\pm 0.06)\mathrm{log}(\langle {\rm{\Psi }}\rangle )+1.00$$(\pm 0.13)\mathrm{log}(\sigma )+7.81(\pm 0.26)$, with an rms = 0.215 (R = 0.64 and $P\lt 1.2\times {10}^{-16}$). This fine-tuning permits us to obtain the FP in terms of two distinct "virtual planes" in the $\mathrm{log}({R}_{e})\mbox{--}\mathrm{log}(\langle {I}_{e}\rangle )\mbox{--}\mathrm{log}(\sigma )$ space. The first one (the virial plane; VP) represents the total galaxy mass derived from the scalar virial theorem and the mass-to-light ratio M/L, while the second plane comes from the relation $L={L}_{0}^{\prime }{\sigma }^{-2}$, where ${L}_{0}^{\prime }$ is a parameter connected with $\langle {\rm{\Psi }}\rangle$. This is a mathematically convenient way for expressing the independence of the galaxy light from the virial equilibrium. Each galaxy in the $\mathrm{log}({R}_{e})\mbox{--}\mathrm{log}(\langle {I}_{e}\rangle )\mbox{--}\mathrm{log}(\sigma )$ space is identified by the intersection of these two planes. A posteriori, we show that the properties of the FP (tilt and scatter) and the zone of exclusion visible in the FP projections are consequences of this fine-tuning. The link between the FP properties and the SFR of galaxies provides a new view of the star formation phenomenon. The star formation history of an unperturbed galaxy seems to be driven by the initial conditions in the protogalaxies and is regulated across cosmic epochs by the variation of the main galaxy parameters (mass, luminosity, structural shape, and velocity dispersion).

The linearly polarized solar limb spectrum caused by the absorption and scattering of anisotropic radiation has a very rich diagnostic potential, given its sensitivity to the thermal, dynamic, and magnetic structure of the solar atmosphere. A crucial first step toward its scientific exploitation is understanding the physical origin of the observed spectral line polarization and its magnetic sensitivity via the Hanle and Zeeman effects. Here, we study the linear polarization signals observed in the IR triplet of O i at 777 nm, describing in detail the multilevel radiative transfer calculations that allowed us to decipher their physical origin. We investigate the sensitivity of the calculated scattering polarization signals to various modeling parameters, finding that the observed fractional linear polarization pattern originates mainly in the solar chromosphere, although the intensity profiles of the O i IR triplet come mainly from the lower photosphere. We find that the three lines are sensitive, via the Hanle effect, to magnetic fields with strengths between 0.01 and 30 G, in a extended region of the solar atmosphere. We show this through calculations of the response function to magnetic field perturbations in a semi-empirical model of the quiet Sun atmosphere. The dominant response of the linear polarization signals occurs at heights $\sim 1000$ km above the visible model's surface, which demonstrates that the scattering linear polarization signals of the oxygen IR triplet encode information on the magnetism of the solar chromosphere.

UV absorption studies with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite have made important observations of H₂ molecular gas in Galactic interstellar translucent and diffuse clouds. Observations of the 158 μm [C ii] fine-structure line with Herschel trace the same H₂ molecular gas in emission. We present [C ii] observations along 27 lines of sight (LOSs) toward target stars of which 25 have FUSE H₂ UV absorption. Two stars have only HST STIS C ii λ2325 absorption data. We detect [C ii] 158 μm emission features in all but one target LOS. For three target LOSs that are close to the Galactic plane, $| {\text{}}b| \,\lt$ 1°, we also present position–velocity maps of [C ii] emission observed by Herschel Heterodyne Instrument in the Far Infrared (HIFI) in on-the-fly spectral-line mapping. We use the velocity-resolved [C ii] spectra observed by the HIFI instrument toward the target LOSs observed by FUSE to identify [C ii] velocity components associated with the H₂ clouds. We analyze the observed velocity integrated [C ii] spectral-line intensities in terms of the densities and thermal pressures in the H₂ gas using the H₂ column densities and temperatures measured by the UV absorption data. We present the H₂ gas densities and thermal pressures for 26 target LOSs and from the [C ii] intensities derive a mean thermal pressure in the range of ∼6100–7700 K cm⁻³ in diffuse H₂ clouds. We discuss the thermal pressures and densities toward 14 targets, comparing them to results obtained using the UV absorption data for two other tracers C i and CO. Our results demonstrate the richness of the far-IR [C ii] spectral data which is a valuable complement to the UV H₂ absorption data for studying diffuse H₂ molecular clouds. While the UV absorption is restricted to the directions of the target star, far-IR [C ii] line emission offers an opportunity to employ velocity-resolved spectral-line mapping capability to study in detail the clouds' spatial and velocity structures.