[en] Deep ACS slitless grism observations and identification of stellar sources are presented within the Great Observatories Origins Deep Survey North and South fields which were obtained in the Probing Evolution And Reionization Spectroscopically (PEARS) program. It is demonstrated that even low-resolution spectra can be a very powerful means of identifying stars in the field, especially low-mass stars with stellar types M0 and later. The PEARS fields lay within the larger GOODS fields, and we used new, deeper images to further refine the selection of stars in the PEARS field, down to a magnitude of z ₈₅₀ = 25 using a newly developed stellarity parameter. The total number of stars with reliable spectroscopic and morphological identification was 95 and 108 in the north and south fields, respectively. The sample of spectroscopically identified stars allows constraints to be set on the thickness of the Galactic thin disk as well as contributions from a thick disk and a halo component. We derive a thin disk scale height, as traced by the population of M4-M9 dwarfs along two independent lines of sight, of h _thin = 370⁺⁶⁰_-65 pc. When including the more massive M0-M4 dwarf population, we derive h _thin = 300 ± 70 pc. In both cases, we observe that we must include a combination of thick and halo components in our models in order to account for the observed numbers of faint dwarfs. The required thick disk scale height is typically h _thick = 1000 pc and the acceptable relative stellar densities of the thin disk to thick disk and the thin disk to halo components are in the range of 0.00025 < f _halo < 0.0005 and 0.05 < f _thick < 0.08 and are somewhat dependent on whether the more massive M0-M4 dwarfs are included in our sample.

[en] We present an analysis of the properties of H I holes detected in 20 galaxies that are part of 'The H I Nearby Galaxy Survey'. We detected more than 1000 holes in total in the sampled galaxies. Where they can be measured, their sizes range from about 100 pc (our resolution limit) to about 2 kpc, their expansion velocities range from 4 to 36 km s^-1, and their ages are estimated to range between 3 and 150 Myr. The holes are found throughout the disks of the galaxies, out to the edge of the H I disk; 23% of the holes fall outside R₂₅. We find that shear limits the age of holes in spirals (shear is less important in dwarf galaxies) which explains why H I holes in dwarfs are rounder, on average than in spirals. Shear, which is particularly strong in the inner part of spiral galaxies, also explains why we find that holes outside R₂₅ are larger and older. We derive the scale height of the H I disk as a function of galactocentric radius and find that the disk flares up in all galaxies. We proceed to derive the surface and volume porosity (Q_2D and Q_3D) and find that this correlates with the type of the host galaxy: later Hubble types tend to be more porous. The size distribution of the holes in our sample follows a power law with a slope of a_ν ∼ -2.9. Assuming that the holes are the result of massive star formation (SF), we derive values for the supernova rate and star formation rate (SFR) which scales with the SFR derived based on other tracers. If we extrapolate the observed number of holes to include those that fall below our resolution limit, down to holes created by a single supernova, we find that our results are compatible with the hypothesis that H I holes result from SF.

[en] We present a sample of 17 newly discovered ultracool dwarf candidates later than ∼M8, drawn from 231.90 arcmin² of Hubble Space Telescope Wide Field Camera 3 infrared imaging. By comparing the observed number counts for 17.5 ≤ J₁₂₅ ≤ 25.5 AB mag to an exponential disk model, we estimate a vertical scale height of z_scl = 290 ± 25 (random) ± 31 (systematic) pc for a binarity fraction of f_b = 0. While our estimate is roughly consistent with published results, we suggest that the differences can be attributed to sample properties, with the present sample containing far more substellar objects than previous work. We predict the object counts should peak at J₁₂₅ ∼ 24 AB mag due to the exponentially declining number density at the edge of the disk. We conclude by arguing that trend in scale height with spectral type may breakdown for brown dwarfs since they do not settle onto the main sequence.

[en] We aim at estimating the dust scale height of protoplanetary disks from millimeter continuum observations. First, we present a general expression of intensity of a ring in a protoplanetary disk and show that we can constrain the dust scale height by the azimuthal intensity variation. Then, we apply the presented methodology to the two distinct rings at 68 au and at 100 au of the protoplanetary disk around HD 163296. We constrain the dust scale height by comparing the high-resolution millimeter dust continuum image obtained in the Disk Substructures at High Angular Resolution Project (DSHARP) with radiative transfer simulations using RADMC-3D. We find that h _d/h _g > 0.84 at the inner ring and h _d/h _g < 0.11 at the outer ring with 3σ uncertainties, where h _d is the dust scale height and h _g is the gas scale height. This indicates that the dust is flared at the inner ring and settled at the outer ring. We further constrain the ratio of the turbulence parameter α to the gas-to-dust-coupling parameter St from the derived dust scale height; α/St > 2.4 at the inner ring, and α/St < $1.1\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->2}$ at the outer ring. This result shows that the turbulence is stronger or the dust is smaller at the inner ring than at the outer ring.

[en] Dust attenuation of an inclined galaxy can cause additional asymmetries in observations, even if the galaxy has a perfectly symmetric structure. Taking advantage of the integral field spectroscopic data observed by the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at the Apache Point Observatory survey, we investigate the asymmetries of the emission-line and continuum maps of star-forming disk galaxies. We define new parameters, A _a and A _b, to estimate the asymmetries of a galaxy about its major and minor axes, respectively. Comparing A _a and A _b in different inclination bins, we attempt to detect the asymmetries caused by dust. For the continuum images, we find that A _a increases with the inclination, while A _b is a constant as inclination changes. Similar trends are found for g − r, g − i, and r − i color images. The dependence of the asymmetry on inclination suggests a thin dust layer with a scale height smaller than the stellar populations. For the Hα and Hβ images, neither A _a nor A _b shows a significant correlation with inclination. Also, we do not find any significant dependence of the asymmetry of E(B − V)_g on inclination, implying that the dust in the thick disk component is not significant. Compared to the SKIRT simulation, the results suggest that the thin dust disk has an optical depth of τ _V ∼ 0.2. This is the first time that the asymmetries caused by the dust attenuation and the inclination are probed statistically with a large sample. Our results indicate that the combination of the dust attenuation and the inclination effects is a potential indicator of the 3D disk orientation.

[en] We report the discovery of HATS-5b, a transiting hot Saturn orbiting a G-type star, by the HATSouth survey. HATS-5b has a mass of M_p ≈ 0.24 M _J, radius of R_p ≈ 0.91 R _J, and transits its host star with a period of P ≈ 4.7634 days. The radius of HATS-5b is consistent with both theoretical and empirical models. The host star has a V-band magnitude of 12.6, mass of 0.94 M _☉, and radius of 0.87 R _☉. The relatively high scale height of HATS-5b and the bright, photometrically quiet host star make this planet a favorable target for future transmission spectroscopy follow-up observations. We reexamine the correlations in radius, equilibrium temperature, and metallicity of the close-in gas giants and find hot Jupiter-mass planets to exhibit the strongest dependence between radius and equilibrium temperature. We find no significant dependence in radius and metallicity for the close-in gas giant population.

[en] NGC 4013 is a distinctly warped galaxy with evidence of disk–halo activity. Through deep H i observations and modeling we confirm that the H i disk is thin (central exponential scale height with an upper limit of 4″ or 280 pc), but flaring. We detect a vertical gradient in rotation velocity (lag), which shallows radially from a value of −35${}_{-<!--\; ???\; -->28}^{+7}$ km s⁻¹ kpc⁻¹ at 1.′4 (5.8 kpc), to a value of zero near R₂₅ (11.2 kpc). Over much of this radial range, the lag is relatively steep. Both the steepness and the radial shallowing are consistent with recent determinations for a number of edge-ons, which have been difficult to explain. We briefly consider the lag measured in NGC 4013 in the context of this larger sample and theoretical models, further illuminating disk–halo flows.

[en] We use the recent measurement of the velocity dispersion of star-forming, outer-disk knots by Herbert-Fort et al. in the nearly face-on galaxy NGC 628, in combination with other data from the literature, to execute a straightforward test of gravity at low accelerations. Specifically, the rotation curve at large radius sets the degree of non-standard acceleration and then the predicted scale height of the knots at that radius provides the test of the scenario. For our demonstration, we presume that the Hα knots, which are young (age < 10 Myr), are distributed like the gas from which they have recently formed and find a marginal (>97% confidence) discrepancy with a modified gravity scenario given the current data. More interestingly, we demonstrate that there is no inherent limitation that prevents such a test from reaching possible discrimination at the >4σ level with a reasonable investment of observational resources.

[en] Recent mid-infrared observations of young stellar objects have found significant variations possibly indicative of changes in the structure of the circumstellar disk. Previous models of this variability have been restricted to axisymmetric perturbations in the disk. We consider simple models of a non-axisymmetric variation in the inner disk, such as a warp or a spiral wave. We find that the precession of these non-axisymmetric structures produces negligible flux variations but a change in the height of these structures can lead to significant changes in the mid-infrared flux. Applying these models to observations of the young stellar object LRLL 31 suggests that the observed variability could be explained by a warped inner disk with variable scale height. This suggests that some of the variability observed in young stellar objects could be explained by non-axisymmetric disturbances in the inner disk and this variability would be easily observable in future studies.

[en] Filamentary structures are recognized as a fundamental component of interstellar molecular clouds in observations made by the Herschel satellite. These filaments, especially massive filaments, often extend in a direction perpendicular to the interstellar magnetic field. Furthermore, the filaments sometimes have an apparently negative temperature gradient—that is, their temperatures decrease toward their centers. In this paper, we study the magnetohydrostatic equilibrium state of negative-indexed polytropic gas with the magnetic field running perpendicular to the axis of the filament. The model is controlled by four parameters: center-to-surface density ratio (ρ _c/ρ _s), plasma β of the surrounding gas, radius of the parent cloud $R_0^{\mathrm{\prime <!--\; ???\; -->}}$ normalized by the scale height, and the polytropic index N. The steepness of the temperature gradient is represented by N. We found that the envelope of the column density profile becomes shallow when the temperature gradient is large. This reconciles the inconsistency between the observed profiles and those expected from the isothermal models. We compared the maximum line mass (mass per unit length), above which there is no equilibrium, with that of the isothermal nonmagnetized filament. We obtained an empirical formula to express the maximum line mass of a magnetized polytropic filament as ${\mathrm{\lambda <!--\; ??\; -->}}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq <!--\; ???\; -->{[{({\mathrm{\lambda <!--\; ??\; -->}}_{0,\mathrm{m}\mathrm{a}\mathrm{x}}(N)/M_{\odot <!--\; ???\; -->}\mathrm{p}{\mathrm{c}}^{-<!--\; ???\; -->1})}^2+{\left[5.9{(1.0+1.2/N)}^{1/2}\left({\mathrm{\Phi <!--\; ??\; -->}}_{\mathrm{c}\mathrm{l}}/1\mathrm{\mu <!--\; ??\; -->}\mathrm{G}\mathrm{p}\mathrm{c}\right)\right]}^2]}^{1/2}$ M _⊙ pc⁻¹, where ${\mathrm{\lambda <!--\; ??\; -->}}_{0,max}(N)$ represents the maximum line mass of the nonmagnetized filament and Φ_cl indicates one-half of the magnetic flux threading the filament per unit length. Although the negative-indexed polytrope makes the maximum line mass decrease, compared with that of the isothermal model, a magnetic field threading the filament increases the line mass.