Keywords

Supernova remnant (SNR) shock waves are the main place where interstellar dust grains are destroyed. However, the dust destruction efficiency in nonradiative shocks is still not well known. One way to estimate the fraction of dust destroyed is to compare the difference between postshock gas abundances and preshock medium total abundances when the preshock elemental depletion factors are known. We compare the postshock gas abundances of 16 SNRs in the Large Magellanic Cloud (LMC) with the LMC interstellar medium abundances that we derived based on 69 slow-rotating early B-type stars. We find that, on average, ∼61% of Si-rich dust grains are destroyed in the shock, while the fraction of dust destroyed is only ∼40% for Fe-rich dust grains. This result supports the idea that the high depletion of Fe in the diffuse neutral medium is not caused by the resilience of Fe-rich grains but because of faster growth rate. This work also presents a potential way to constrain the chemical composition of interstellar dust.

We report on polarimetric maps made with HAWC+/SOFIA toward ρ Oph A, the densest portion of the ρ Ophiuchi molecular complex. We employed HAWC+ bands C (89 μm) and D (154 μm). The slope of the polarization spectrum was investigated by defining the quantity ${{ \mathcal R }}_{{DC}}={p}_{D}/{p}_{C}$, where p_C and p_D represent polarization degrees in bands C and D, respectively. We find a clear correlation between ${{ \mathcal R }}_{{DC}}$ and the molecular hydrogen column density across the cloud. A positive slope (${{ \mathcal R }}_{{DC}}$  > 1) dominates the lower-density and well-illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope (${{ \mathcal R }}_{{DC}}$  < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of ${{ \mathcal R }}_{{DC}}$ is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.

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

We report the first detection of C₂ ${A}^{1}{{\rm{\Pi }}}_{u}-{X}^{1}{{\rm{\Sigma }}}_{g}^{+}$ (0,0) and CN ${A}^{2}{{\rm{\Pi }}}_{u}-{X}^{2}{{\rm{\Sigma }}}^{+}$ (0,0) absorption bands in the interstellar medium. The detection was made using the near-infrared (0.91–1.35 μm) high-resolution (R = 20,000 and 68,000) spectra of Cygnus OB2 No. 12 collected with the WINERED spectrograph mounted on the 1.3 m Araki telescope. The A–X (1,0) bands of C₂ and CN were detected simultaneously. These near-infrared bands have larger oscillator strengths, compared with the A–X (2,0) bands of C₂ and CN in the optical. In the spectrum of the C₂ (0,0) band with R = 68,000, three velocity components in the line of sight could be resolved and the lines were detected up to high rotational levels (J'' ∼ 20). By analyzing the rotational distribution of C₂, we could estimate the kinetic temperature and gas density of the clouds with high accuracy. Furthermore, we marginally detected weak lines of ¹²C¹³C for the first time in the interstellar medium. Assuming that the rotational distribution and the oscillator strengths of the relevant transitions of ¹²C₂ and ¹²C¹³C are the same, the carbon isotope ratio was estimated to be ¹²C/¹³C = 50–100, which is consistent with the ratio in the local interstellar medium. We also constrained the oscillator strength ratio of the C₂ (0,0) and (1,0) bands, for which there exists a discrepancy between theoretical calculations and experimental results. This unique constraint obtained from astronomical observation will contribute to improving the accuracy of the oscillator strength measurement, which will lead to further advancements of the C₂ excitation model and allow the physical conditions of clouds to be derived.

We investigate how the properties of Galactic giant molecular clouds (GMCs) and their denser substructures (clumps) correlate with the local star formation rate (SFR). We trace clouds using the ¹²CO(3−2) transition, as observed by the CO High Resolution Survey. We identify their constituent clumps using thermal dust emission, as observed by the Herschel infrared GALactic plane survey. We estimate SFRs in these clouds using 70 μm emission. In total, we match 3674 clumps to 473 clouds in position–position–velocity space spanning the Galactic longitude range 10° < ℓ < 56°. We find that more massive clouds produce more clumps and more massive clumps. These clumps have average number densities an order of magnitude greater than their host clouds. We find a mean clump mass fraction of ${0.20}_{-0.10}^{+0.13}$. This mass fraction weakly varies with mass and mass surface density of clouds, and shows no clear dependence on the virial parameter and line width of the clouds. The average clump mass fraction is only weakly dependent upon Galactocentric radius. Although the scatter in our measured properties is significant, the SFR for clouds is independent of clump mass fraction. However, there is a positive correlation between the depletion times for clouds and clump mass fraction. We find a star formation efficiency per freefall time of _ff = 0.15% for GMCs but _ff = 0.37% for clumps.

Dust lanes bisect the plane of a typical edge-on spiral galaxy as a dark optical absorption feature. Their appearance is linked to the gravitational stability of spiral disks; the fraction of edge-on galaxies that displays a dust lane is a direct indicator of the typical vertical balance between gravity and turbulence: a balance struck between the energy input from star formation and the gravitational pull into the plane of the disk. Based on morphological classifications by the Galaxy Zoo project on the Kilo Degree Survey (KiDS) imaging data in the Galaxy and Mass Assembly (GAMA) fields, we explore the relation of dust lanes to the galaxy characteristics, most of which were determined using the Magphys spectral energy distribution fitting tool: stellar mass, total and specific star formation rates, and several parameters describing the cold dust component. We find that the fraction of dust lanes does depend on the stellar mass of the galaxy; they start to appear at M* ∼ 10⁹ M_⊙. A dust lane also strongly implies a dust mass of at least 10⁵ M_⊙, but otherwise does not correlate with cold dust mass parameters of the Magphys spectral energy distribution analysis, nor is there a link with the star formation rate, specific or total. Dust lane identification does not depend on disk ellipticity (disk thickness) or Sérsic profile but correlates with bulge morphology; a round bulge favors dust lane votes. The central component along the line of sight that produces the dust lane is not associated with either one of the components fit by Magphys, the cold diffuse component or the localized, heated component in H ii regions, but a mix of these two.

We present a set of new analytic solutions aimed at self-consistently describing the spatially averaged time evolution of the gas, stellar, metal, and dust content in an individual star-forming galaxy hosted within a dark halo of a given mass and formation redshift. Then, as an application, we show that our solutions, when coupled to specific prescriptions for parameter setting (inspired by in situ galaxy–black hole coevolution scenarios) and merger rates (based on numerical simulations), can be exploited to reproduce the main statistical relationships followed by early-type galaxies and their high-redshift star-forming progenitors. Our analytic solutions allow one to easily disentangle the diverse role of the main physical processes regulating galaxy formation, quickly explore the related parameter space, and make transparent predictions on spatially averaged quantities. As such, our analytic solutions may provide a basis for improving the (subgrid) physical recipes presently implemented in theoretical approaches and numerical simulations and can offer a benchmark for interpreting and forecasting current and future broadband observations of high-redshift star-forming galaxies.

The dependence of the polarization fraction p on total intensity I in polarized submillimeter emission measurements is typically parameterized as p ∝ I^−α (α ≤ 1) and used to infer dust grain alignment efficiency in star-forming regions, with an index α = 1 indicating near-total lack of alignment of grains with the magnetic field. In this work, we demonstrate that the non-Gaussian noise characteristics of the polarization fraction may produce apparent measurements of α ∼ 1 even in data with significant signal-to-noise in Stokes Q, U, and I emission, and so with robust measurements of polarization angle. We present a simple model demonstrating this behavior and propose a criterion by which well-characterized measurements of the polarization fraction may be identified. We demonstrate that where our model is applicable, α can be recovered by fitting the p–I relationship with the mean of the Rice distribution without statistical debiasing of the polarization fraction. We apply our model to JCMT BISTRO Survey POL-2 850 μm observations of three clumps in the Ophiuchus molecular cloud, finding that in the externally illuminated Oph A region, α ≈ 0.34, while in the more isolated Oph B and C, despite their differing star formation histories, α ∼ 0.6–0.7. Our results thus suggest that dust grain alignment in dense gas is more strongly influenced by the incident interstellar radiation field than by star formation history. We further find that grains may remain aligned with the magnetic field at significantly higher gas densities than has previously been believed, thus allowing investigation of magnetic field properties within star-forming clumps and cores.

A new experimental setup, INterStellar Ice-Dust Experiment (INSIDE), was designed for studying cosmic grain analogs represented by ice-coated carbon- and silicate-based dust grains. With the new instrument, we can simulate the physical and chemical conditions prevailing in interstellar and circumstellar environments. The setup combines ultrahigh vacuum and low-temperature conditions with infrared spectroscopy and mass spectrometry. Using INSIDE, we plan to investigate physical and chemical processes, such as adsorption, desorption, molecule formation, on the surface of dust/ice samples. First experiments on the photodesorption of water ice molecules from the surface of silicate and carbon grains by UV photons revealed a strong influence of the surface properties on the desorption yield, in particular in the monolayer regime. In the second experiment, the thermal desorption of cometary ice analogs composed of six molecular components was studied for the first time. Codesorption of CO₂ and CH₃OH with O₂ indicates that at high O₂ concentrations in cometary or interstellar ices, "heavy" ice molecules can be partly trapped in O₂ and enter the gas phase much earlier than expected. This effect could explain astronomical detections of complex organic molecules in cold dense interstellar clouds.

We present a uniform catalog of accurate distances to local molecular clouds informed by the Gaia DR2 data release. Our methodology builds on that of Schlafly et al. First, we infer the distance and extinction to stars along sightlines toward the clouds using optical and near-infrared photometry. When available, we incorporate knowledge of the stellar distances obtained from Gaia DR2 parallax measurements. We model these per-star distance–extinction estimates as being caused by a dust screen with a 2D morphology derived from Planck at an unknown distance, which we then fit for using a nested sampling algorithm. We provide updated distances to the Schlafly et al. sightlines toward the Dame et al. and Magnani et al. clouds, finding good agreement with the earlier work. For a subset of 27 clouds, we construct interactive pixelated distance maps to further study detailed cloud structure, and find several clouds which display clear distance gradients and/or are comprised of multiple components. We use these maps to determine robust average distances to these clouds. The characteristic combined uncertainty on our distances is ≈5%–6%, though this can be higher for clouds at greater distances, due to the limitations of our single-cloud model.