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Aims. Interstellar dust (ISD) particles penetrate the heliosphere because of the relative motion of the local interstellar cloud and the Sun. The penetrated particles pass through the heliospheric interface, that is, the region in which solar wind and interstellar plasma interact. As a result, the ISD flow is modified after the passage through this region under the influence of electromagnetic force. The main goal of this work is to show how the heliospheric interface affects the distribution of ISD particles near the Sun. Methods. We have developed a Monte Carlo model of the ISD distribution in the heliosphere. It first takes the effects of the heliospheric interface and the rotating heliospheric current sheet into account. The effects of the heliospheric interface were probed using a global heliospheric model. Results. The computation results show that the heliospheric interface strongly influences the distribution of relatively small (radius a = 150 − 250 nm) astronomical silicates. The unexpected finding is that the heliospheric interface facilitates the penetration of a = 150 nm particles at small heliocentric distances and, particularly, to the Ulysses orbit (1 − 5 AU). We demonstrate that the deflection of ISD particles in the outer heliosheath is the principal mechanism that causes the effects of the heliospheric interface on the distribution near the Sun. The computations with different heliospheric models show that the distribution near the Sun is sensitive to the plasma parameters in the pristine local interstellar medium. Thus, we demonstrated that being measured near the Sun, the ISD may serve as a new independent diagnostics of the local interstellar medium and the heliospheric boundaries. [ABSTRACT FROM AUTHOR]

Context. Interstellar surface chemistry is a complex process that occurs in icy layers that have accumulated onto grains of different sizes. The efficiency of the surface processes often depends on the immediate environment of the adsorbed molecules. Aims. We investigated how gas-grain chemistry changes when the surface molecule binding energy is modified, depending on the properties of the surface. Methods. In a gas-grain astrochemical model, molecular binding energy gradually changes for three different environments –(1) the bare grain surface, (2) polar water-dominated ices, and (3) weakly polar carbon monoxide-dominated ices. In addition to diffusion, evaporation, and chemical desorption, photodesorption was also made binding energy-dependent, in line with experimental results. These phenomena occur in a collapsing prestellar core model that considers five grain sizes with ices arranged into four layers. Results. Variable desorption energy moderately affects gas-grain chemistry. Bare-grain effects slow down ice accumulation, while easier diffusion of molecules on weakly polar ices promotes the production of carbon dioxide. Efficient chemical desorption from bare grains significantly delays the appearance of the first ice monolayer. Conclusions. The combination of multiple aspects of grain surface chemistry creates a gas-ice balance that is different from simpler models. The composition of the interstellar ices is regulated by several binding-energy dependent desorption mechanisms. Their actions overlap in time and space, explaining the similar proportions of major ice components (water and carbon oxides) observed in all directions. [ABSTRACT FROM AUTHOR]

Context. Maps of polarized dust emission of molecular clouds reveal the morphology of the magnetic field associated with star-forming regions. In particular, polarization maps of hub-filament systems show the distortion of magnetic field lines induced by gas flows onto and inside filaments. Aims. We aim to understand the relation between the curvature of magnetic field lines associated with filaments in hub-filament systems and the properties of the underlying gas flows. Methods. We consider steady-state models of gas with finite electrical resistivity flowing across a transverse magnetic field. We derive the relation between the bending of the field lines and the flow parameters represented by the Alfvén Mach number and the magnetic Reynolds number. Results. We find that, on the scale of the filaments, the relevant parameter for a gas of finite electrical resistivity is the magnetic Reynolds number, and we derive the relation between the deflection angle of the field from the initial direction (assumed perpendicular to the filament) and the value of the electrical resistivity, due to either Ohmic dissipation or ambipolar diffusion. Conclusions. Application of this model to specific observations of polarized dust emission in filamentary clouds shows that magnetic Reynolds numbers of a few tens are required to reproduce the data. Despite significant uncertainties in the observations (the flow speed, the geometry and orientation of the filament), and the idealization of the model, the specific cases considered show that ambipolar diffusion can provide the resistivity needed to maintain a steady state flow across magnetic fields of significant strength over realistic time scales. [ABSTRACT FROM AUTHOR]

Context. The James Webb Space Telescope (JWST) has captured the sharpest infrared images ever taken of the Horsehead nebula, a prototypical moderately irradiated photon-dominated region (PDR) that is fully representative of most of the UV-illuminated molecular gas in the Milky Way and star-forming galaxies. Aims. We investigate the impact of far-ultraviolet (FUV) radiation emitted by a massive star on the edge of a molecular cloud in terms of photoevaporation, ionization, dissociation, H2 excitation, and dust heating. We also aim to constrain the structure of the edge of the PDR and its illumination conditions. Methods. We used NIRCam and MIRI to obtain 17 broadband and 6 narrowband maps of the illuminated edge of the Horsehead across a wide spectral range from 0.7 to 28 µm. We mapped the dust emission, including the aromatic and aliphatic infrared (IR) bands, scattered light, and several gas phase lines (e.g., Paa, Brα, H2 1-0 S(1) at 2.12 µm). For our analysis, we also associated two HST-WFC3 maps at 1.1 and 1.6 µm, along with HST-STIS spectroscopic observations of the Ha line. Results. We probed the structure of the edge of the Horsehead and resolved its spatial complexity with an angular resolution of 0.1 to 1″ (equivalent to 2 × 10−4 to 2 × 10−3 pc or 40 to 400 au at the distance of 400 pc). We detected a network of faint striated features extending perpendicularly to the PDR front into the HII region in NIRCam and MIRI filters sensitive to nano-grain emission, as well as in the HST filter at 1.1 µm, which traces light scattered by larger grains. This may indeed figure as the first detection of the entrainment of dust particles in the evaporative flow. The filamentary structure of the 1-0 S(1) line of H2 at the illuminated edge of the PDR presents numerous sharp sub-structures on scales as small as 1.5″. An excess of H2 emission compared to dust emission is found all along the edge, in a narrow layer (width around 1″, corresponding to 2 × 10−3 pc or 400 au) directly illuminated by σ-Orionis. The ionization front and the dissociation front appear at distances 1–2″ behind the external edge of the PDR and seem to spatially coincide, indicating a very small thickness of the neutral atomic layer (below 100 au). All broadband maps present strong color variations between the illuminated edge and the internal regions. This can be explained by dust attenuation in a scenario where the illuminating star σ-Orionis is slightly inclined compared to the plane of the sky, so that the Horsehead is illuminated from behind at an oblique angle. The deviations from predictions of the measured emissions in the Hα, Paα, and Brα lines also indicate dust attenuation. With a very simple model, we used the data to derive the main spectral features of the extinction curve. A small excess of extinction at 3 µm may be attributed to icy H2O mantles onto grains formed in dense regions. We also derived attenuation profiles from 0.7 to 25 µm across the PDR. In all lines of sight crossing the inner regions of the Horsehead, especially around the IR peak position, it appears that dust attenuation is non-negligible over the entire spectral range of the JWST. [ABSTRACT FROM AUTHOR]

Context. A crucial aspect in addressing the challenge of measuring the core mass function (CMF), that is pivotal for comprehending the origin of the initial mass function (IMF), lies in constraining the temperatures of the cores. Aims. We aim to measure the luminosity, mass, column density and dust temperature of star-forming regions imaged by the ALMA-IMF large program. These fields were chosen to encompass early evolutionary stages of massive protoclusters. High angular resolution mapping is required to capture the properties of protostellar and pre-stellar cores within these regions, and to effectively separate them from larger features, such as dusty filaments. Methods. We employed the point process mapping (PPMAP) technique, enabling us to perform spectral energy distribution fitting of far-infrared and submillimeter observations across the 15 ALMA-IMF fields, at an unmatched 2.5″ angular resolution. By combining the modified blackbody model with near-infrared data, we derived bolometric luminosity maps. We estimated the errors impacting values of each pixel in the temperature, column density, and luminosity maps. Subsequently, we employed the extraction algorithm getsf on the luminosity maps in order to detect luminosity peaks and measure their associated masses. Results. We obtained high-resolution constraints on the luminosity, dust temperature, and mass of protoclusters, that are in agreement with previously reported measurements made at a coarser angular resolution. We find that the luminosity-to-mass ratio correlates with the evolutionary stage of the studied regions, albeit with intra-region variability. We compiled a PPMAP source catalog of 313 luminosity peaks using getsf on the derived bolometric luminosity maps. The PPMAP source catalog provides constraints on the mass and luminosity of protostars and cores, although one source may encompass several objects. Finally, we compare the estimated luminosity-to-mass ratio of PPMAP sources with evolutionary tracks and discuss the limitations imposed by the 2.5″ beam. [ABSTRACT FROM AUTHOR]

Narrow absorption features in nearby supernova (SN) spectra are a powerful diagnostic of the slow-moving material in the line of sight: they are extensively used to infer dust extinction from the host galaxies, and they can also serve in the detection of circumstellar material originating from the SN progenitor and present in the vicinity of the explosion. Despite their wide use, very few studies have examined the biases of the methods to characterize narrow lines, and not many statistical analyses exist. This is the first paper of a series in which we present a statistical analysis of narrow lines of SN spectra of various resolutions. We developed a robust automated methodology to measure the equivalent width (EW) and velocity of narrow absorption lines from intervening material in the line of sight of SNe, including Na I D, Ca II H&K, K I, and diffuse interstellar bands. We carefully studied systematic biases in heterogeneous spectra from the literature by simulating different signal-to-noise, spectral resolution, size and orientation of the slit, and we present the real capabilities and limitations of using low- and mid-resolution spectra to study these lines. In particular, we find that the measurement of the EW of the narrow lines in low-resolution spectra is highly affected by the evolving broad P-Cygni profiles of the SN ejecta, both for core-collapse and type Ia SNe, inducing a conspicuous apparent evolution. Such pervading non-physical evolution of narrow lines might lead to wrong conclusions on the line-of-sight material, for example concerning circumstellar material ejected from the SN progenitors. We thus present an easy way to detect and exclude those cases to obtain more robust and reliable measurements. Finally, after considering all possible effects, we analysed the temporal evolution of the narrow features in a large sample of nearby SNe to detect any possible variation in their EWs over time. We find no time evolution of the narrow line features in our large sample for all SN types. [ABSTRACT FROM AUTHOR]

Context. Previous high-angular-resolution 225 GHz (~1.3 mm) continuum observations of the transitional disk DM Tau have resolved an outer ring at 20–120 au radii that is weakly azimuthally asymmetric. Aims. We aim to examine dust growth and filtration in the outer ring of DM Tau. Methods. We performed ~0″.06 (~8.7 au) resolution Karl G. Jansky Very Large Array (JVLA) 40–48 GHz (~7 mm; Q band) continuum observations, along with complementary observations at lower frequencies. In addition, we analyzed the archival JVLA observations undertaken since 2010. Results. Intriguingly, the Q band image resolved the azimuthally highly asymmetric, knotty dust emission sources close to the inner edge of the outer ring. Fitting the 8–700 GHz spectral energy distribution (SED) with two dust components indicates that the maximum grain size (amax) in these knotty dust emission sources is likely ≳300 µm, whereas it is ≳50 µm in the rest of the ring. These results may be explained by a trapping of inwardly migrating "grown" dust close to the ring inner edge. The exact mechanism for developing the azimuthal asymmetry has not yet been identified, which may be due to planet-disk interaction that might also be responsible for the creation of the dust cavity and pressure bump. Otherwise, it may be due to the fluid instabilities and vortex formation as a result of shear motions. Finally, we remark that the asymmetries in DM Tau are difficult to diagnose from the ≳225 GHz observations, owing to a high optical depth at the ring. In other words, the apparent symmetric or asymmetric morphology of the transitional disks may be related to the optical depths of those disks at the observing frequency. [ABSTRACT FROM AUTHOR]

Context. The chemical evolution of distant galaxies cannot be assessed from observations of individual stars, in contrast to the case of nearby galaxies. On the other hand, the study of the interstellar medium (ISM) offers an alternative way to reveal important properties of the chemical evolution of distant galaxies. The chemical enrichment of the ISM is produced by all the previous generations of stars and it is possible to precisely determine the metal abundances in the neutral ISM in galaxies. The chemical abundance patterns in the neutral ISM are determined by the gas metallicity, presence of dust (the depletion of metals into dust grains), and possible deviations due to specific nucleosynthesis, for example, α-element enhancements. Aims. We aim to derive the metallicities, dust depletion, and α-element enhancements in the neutral ISM of gas-rich mostly-metal-poor distant galaxies (Damped Lyman-α absorbers, DLAs). Furthermore, we aim to constrain the distribution of α-element enhancements with metallicity in these galaxies. Methods. We collected a literature sample of column density measurements of O, Mg, Si, S, Ti, Cr, Fe, Ni, Zn, P, and Mn in the neutral ISM of DLAs at redshifts of 0.60 < z < 3.40. We used this sample to define a golden sample of DLAs with constrained observations of Ti and at least one other α-element. By studying the abundance patterns, we determined the amount of dust depletion, solely based on the observed relative abundances of the α-elements. We then used the abundances of Fe-peak elements to determine the overall metallicity of each system, after correcting for dust depletion. In addition, we studied the deviations from the basic (linear) abundance patterns. We divided our sample into two groups of galaxies based on the widths of their absorption lines (Δv90 above or below 100 km s−1), which may be considered as a proxy for their dynamical mass. We characterised the distribution of the α-element enhancements as a function of metallicity for the galaxy population as a whole, by fitting a piecewise function (plateau, decline, plateau) to the data. Results. We observed systematic deviations from the basic abundance patterns for O, Mg, Si, S, Ti, and Mn, which we interpreted as α-element enhancements and a Mn underabundance. The distribution of the α-element enhancements with metallicity is different in the high-Δv90 and low-Δv90 groups of galaxies. We constrained the metallicity of the α-element knee for the high-Δv90 and low-Δv90 groups of galaxies to be −1.02±0.15 dex and −1.84±0.11 dex, respectively. The average α-element enhancement at the high-plateau is [α/Fe]=0.38±0.07 dex. On the other hand, Mn shows an underabundance in all DLAs in the golden sample of −0.36±0.07 dex, on average. Conclusions. We have constrained, for the first time, the distribution of the α-element enhancement with metallicity in the neutral ISM in distant galaxies. Less massive galaxies show an α-element knee at lower metallicities than more massive galaxies. This can be explained by a lower star formation rate in less massive galaxies. If this collective behaviour can be interpreted in the same way as it is for individual systems, this would suggest that more massive and metal-rich systems evolve to higher metallicities before the contribution of SN-Ia to [α/Fe] levels out that of core-collapse SNe. This finding may plausibly be supported by different SFRs in galaxies of different masses. Overall, our results offer important clues to the study of chemical evolution in distant galaxies. [ABSTRACT FROM AUTHOR]

We propose a new method for estimating the distances of molecular clouds traced by CO line emission. Stars from 2MASS and Gaia EDR3 are selected as on-cloud stars when they are projected on a cloud. The background on-cloud stars have redder colors on average than the foreground stars. Instead of searching for stars projected away from the cloud, we employed the TRILEGA galaxy model to mimic the stellar population without cloud extinction along the sightline toward the cloud. Our method does not require an exact boundary of a cloud. The boundaries are highly variable and depend on the sensitivity of the molecular line data. For each cloud, we compared the distributions of on-cloud stars to the TRILEGAL stellar populations in the diagram of J−Ks color versus distance. The intrinsic J−Ks colors of main-sequence and evolved stars from TRILEGAL were considered separately, and they were used as the baseline for subtracting the observed J−Ks colors. The baseline-corrected J−Ks color was deployed with the Bayesian analysis and Markov chain Monte Carlo sampling to determine the distance at which the J−Ks color jump is largest. This method was successfully applied to measure the distances of 27 molecular clouds, which were selected from previously published cloud samples. By replacing TRILEGAL with the GALAXIA galaxy model, we were able to measure the distances for 21 of the 27 clouds. The distances of the 21 clouds based on the GALAXIA model agree well with those based on the TRILEGAL model. The distances of the 27 clouds estimated by this method are consistent with previous estimates. We will apply this new method to a larger region of the gaseous galactic plane, in particular, for the inner galactic region, where a region free of CO emission is hard to separate from the crowded field of clouds. [ABSTRACT FROM AUTHOR]

Context. The first hydrostatic core (FHSC) phase is a brief stage in the protostellar evolution that is difficult to detect. Its chemical composition determine that of later evolutionary stages. Numerical simulations are the tool of choice to study these objects. Aims. Our goal is to characterize the chemical evolution of gas and dust during the formation of the FHSC. Moreover, we are interested in analyzing, for the first time with 3D magnetohydrodynamic (MHD) simulations, the role of grain growth in its chemistry. Methods. We postprocessed 2 × 105 tracer particles from a RAMSES non-ideal MHD simulation using the codes NAUTILUS and SHARK to follow the chemistry and grain growth throughout the simulation. Results. Gas-phase abundances of most of the C, O, N, and S reservoirs in the hot corino at the end of the simulation match the ice-phase abundances from the prestellar phase. Interstellar complex organic molecules such as methyl formate, acetaldehyde, and formamide are formed during the warm-up process. Grain size in the hot corino (nH > 1011 cm−3) increases forty-fold during the last 30 kyr, with negligible effects on its chemical composition. At moderate densities (1010 < nH < 1011 cm−3) and cool temperatures 15 < T < 50 K, increasing grain sizes delay molecular depletion. At low densities (nH ~ 107 cm−3), grains do not grow significantly. To assess the need to perform chemo-MHD calculations, we compared our results with a two-step model that reproduces well the abundances of C and O reservoirs, but not the N and S reservoirs. Conclusions. The chemical composition of the FHSC is heavily determined by that of the parent prestellar core. Chemo-MHD computations are needed for an accurate prediction of the abundances of the main N and S elemental reservoirs. The impact of grain growth in moderately dense areas delaying depletion permits the use of abundance ratios as grain growth proxies. [ABSTRACT FROM AUTHOR]

Context. High-resolution 3D maps of interstellar dust are critical for probing the underlying physics shaping the structure of the interstellar medium, and for foreground correction of astrophysical observations affected by dust. Aims. We aim to construct a new 3D map of the spatial distribution of interstellar dust extinction out to a distance of 1.25 kpc from the Sun. Methods. We leveraged distance and extinction estimates to 54 million nearby stars derived from the Gaia BP/RP spectra. Using the stellar distance and extinction information, we inferred the spatial distribution of dust extinction. We modeled the logarithmic dust extinction with a Gaussian process in a spherical coordinate system via iterative charted refinement and a correlation kernel inferred in previous work. In total, our posterior has over 661 million degrees of freedom. We probed the posterior distribution using the variational inference method MGVI. Results. Our 3D dust map has an angular resolution of up to 14′ (Nside = 256), and we achieve parsec-scale distance resolution, sampling the dust in 516 logarithmically spaced distance bins spanning 69 pc to 1250 pc. We generated 12 samples from the variational posterior of the 3D dust distribution and release the samples alongside the mean 3D dust map and its corresponding uncertainty. Conclusions. Our map resolves the internal structure of hundreds of molecular clouds in the solar neighborhood and will be broadly useful for studies of star formation, Galactic structure, and young stellar populations. It is available for download in a variety of coordinate systems online and can also be queried via the publicly available dustmaps Python package. [ABSTRACT FROM AUTHOR]

Aims. We introduce a new deep-learning approach for the reconstruction of 3D dust density and temperature distributions from multi-wavelength dust emission observations on the scale of individual star-forming cloud cores (<0.2 pc). Methods. We constructed a training data set by processing cloud cores from the Cloud Factory simulations with the POLARIS radiative transfer code to produce synthetic dust emission observations at 23 wavelengths between 12 and 1300 µm. We simplified the task by reconstructing the cloud structure along individual lines of sight (LoSs) and trained a conditional invertible neural network (cINN) for this purpose. The cINN belongs to the group of normalising flow methods and it is able to predict full posterior distributions for the target dust properties. We tested different cINN setups, ranging from a scenario that includes all 23 wavelengths down to a more realistically limited case with observations at only seven wavelengths. We evaluated the predictive performance of these models on synthetic test data. Results. We report an excellent reconstruction performance for the 23-wavelength cINN model, achieving median absolute relative errors of about 1.8% in log(n/m−3) and 1% in log(Tdust/K), respectively. We identify trends towards an overestimation at the low end of the density range and towards an underestimation at the high end of both the density and temperature values, which may be related to a bias in the training data. After limiting our coverage to a combination of only seven wavelengths, we still find a satisfactory performance with average absolute relative errors of about 2.8% and 1.7% in log(n/m−3) and log(Tdust/K). Conclusions. This proof-of-concept study shows that the cINN-based approach for 3D reconstruction of dust density and temperature is very promising and it is even compatible with a more realistically constrained wavelength coverage. [ABSTRACT FROM AUTHOR]

Context. The fragmentation of high-mass star-forming regions depends on a variety of physical parameters, including density, the magnetic field, and turbulent gas properties. Aims. We evaluate the importance of the density and magnetic field structures in relation to the fragmentation properties during high-mass star formation. Methods. Observing the large parsec-scale Stokes I millimeter dust continuum emission with the IRAM 30 m telescope and the intermediate-scale (<0.1 pc) polarized submillimeter dust emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify the dependence of the fragmentation behavior of these regions on the density and magnetic field structures. Results. Based on the IRAM 30 m data, we infer density distributions n ∝ r−p of the regions with typical power-law slopes p around ~1.5. There is no obvious correlation between the power-law slopes of the density structures on larger clump scales (~1 pc) and the number of fragments on smaller core scales (<0.1 pc). Comparing the large-scale single-dish density profiles to those derived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law slopes are steeper, typically around ~2.0. The flattening toward larger scales is consistent with the star-forming regions being embedded in larger cloud structures that do not decrease in density away from a particular core. The magnetic fields of several regions appear to be aligned with filamentary structures that lead toward the densest central cores. Furthermore, we find different polarization structures; some regions exhibit central polarization holes, whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized intensities are inversely related to the Stokes I intensities, following roughly a power-law slope of ∝ SI−0.62. We estimate magnetic field strengths between ~0.2 and ~4.5 mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions. A comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample. The mass-to-flux ratios range between ~2 and ~7, consistent with collapsing star-forming regions. Conclusions. Finding no clear correlations between the present-day large-scale density structure, the magnetic field strength, and the smaller-scale fragmentation properties of the regions, indicates that the fragmentation of high-mass star-forming regions may not be affected strongly by the initial density profiles and magnetic field properties. However, considering the limited evolutionary range and spatial scales of the presented CORE analysis, future research directions should include density structure analysis of younger regions that better resemble the initial conditions, as well as connecting the observed intermediate-scale magnetic field structure with the larger-scale magnetic fields of the parental molecular clouds. [ABSTRACT FROM AUTHOR]

Context. Galactic cosmic rays (CRs) play a crucial role in ionisation, dissociation, and excitation processes within dense cloud regions where UV radiation is absorbed by dust grains and gas species. CRs regulate the abundance of ions and radicals, leading to the formation of more and more complex molecular species, and determine the charge distribution on dust grains. A quantitative analysis of these effects is essential for understanding the dynamical and chemical evolution of star-forming regions. Aims. The CR-induced photon flux has a significant impact on the evolution of the dense molecular medium in its gas and dust components. This study evaluates the flux of UV photons generated by CRs to calculate the photon-induced dissociation and ionisation rates of a vast number of atomic and molecular species, as well as the integrated UV photon flux. Methods. To achieve these goals, we took advantage of recent developments in the determination of the spectra of secondary electrons, in the calculation of state-resolved excitation cross sections of H2 by electron impact, and of photodissociation and photoionisation cross sections. Results. We calculated the H2 level population of each rovibrational level of the X, B, C, B′, D, B″, D′, and a states. We then computed the UV photon spectrum of H2 in its line and continuum components between 72 and 700 nm, with unprecedented accuracy, as a function of the CR spectrum incident on a molecular cloud, the H2 column density, the isomeric H2 composition, and the dust properties. The resulting photodissociation and photoionisation rates are, on average, lower than previous determinations by a factor of about 2, with deviations of up to a factor of 5 for the photodissociation of species such as AlH, C2H2, C2H3, C3H3, LiH, N2, NaCl, NaH, O2+, S2, SiH, l-C4, and l-C5H. A special focus is given to the photoionisation rates of H2, HF, and N2, as well as to the photodissociation of H2, which we find to be orders of magnitude higher than previous estimates. We give parameterisations for both the photorates and the integrated UV photon flux as a function of the CR ionisation rate, which implicitly depends on the H2 column density, as well as the dust properties. [ABSTRACT FROM AUTHOR]

Context. Carbon monoxide (CO) is a poor tracer of H2 in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules, unlike the situation at higher extinctions. Aims. We present a novel, indirect method for constraining H2 column densities (NH2) without employing CO observations. We show that previously recognized nonlinearities in the relation between the extinction, AV (H2), derived from dust emission and the H I column density (NH I) are due to the presence of molecular gas. Methods. We employed archival (NH2) data, obtained from the UV spectra of stars, and calculated AV(H2) toward these sight lines using 3D extinction maps. The following relation fits the data: log NH2 = 1.38742 (log AV(H2))3 − 0.05359 (log AV(H2))2 + 0.25722 log AV(H2) + 20.67191. This relation is useful for constraining NH2 in the diffuse ISM as it requires only NH I and dust extinction data, which are both easily accessible. In 95% of the cases, the estimates produced by the fitted equation have deviations of less than a factor of 3.5. We constructed a NH2 map of our Galaxy and compared it to the CO integrated intensity (WCO) distribution. Results. We find that the average ratio (XCO) between NH2 and WCO is approximately equal to 2 × 1020 cm−2 (K km s−1)−1, consistent with previous estimates. However, we find that the XCO factor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions with NH2 ≳ 1020 cm−2, we estimate that the average H2 fractional abundance, fH2 = 2 NH2/(2NH2 + NH I), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (AV ≥ 1 mag), hence limiting fH2 in these directions. Conclusions. More than 50% of the lines of sight with NH2 ≥ 1020 cm−2 are untraceable by CO with a J = 1−0 sensitivity limit WCO = 1 K km s−1. [ABSTRACT FROM AUTHOR]

Context. Observations of interstellar material infalling onto star- and planet-forming systems have become increasingly common thanks to recent advancements in radio interferometry. These structures have the potential to alter the dynamics of protoplanetary disks significantly by triggering the formation of substructures, inducing shocks, and modifying their physical and chemical properties. Moreover, the protoplanetary disks are replenished with new material, which increases the overall mass budget for planet formation. Aims. In this study, we combine new ALMA band 3 and archival band 6 observations to characterize the dust content and infall rate of a 4000 au arc-like structure that is infalling onto [MGM2012] 512 (hereafter M512), a class I young stellar object located in the Lynds 1641 region of the Orion A molecular cloud. Methods. We detected the extended dust emission from this structure in both ALMA bands. We tested whether the velocity pattern of the streamer is consistent with infalling trajectories by means of analytical streamline models. We measured spectral index maps for the first time and derived a dust opacity-index profile along a streamer. We constrained its grain properties and mass. Results. We find that the arc structure is consistent with infalling motions. We measure a spectral index α ~ 3.2 across the entire structure and a dust opacity index β ~ 1.6. Considering grain properties consistent with the measured β, the structure can host up to 245 M⊕ of dust, which exceeds or is comparable to the mass of the inner unresolved 600 au, which contains the protoplanetary disk of M512. Assuming a typical dust-to-gas ratio of 1% for the streamer, the free-fall timescales (50 kyr) imply total mass-infall rates up to 1.5 × 10−6M⊙ yr−1. M512 has been classified as an outbursting source with multi-epoch WISE photometry. It is thus an interesting case study for exploring the possible connection between infalling streamers and accretion outbursts. Conclusions. M512 is a unique source for which dust continuum emission of an arc-like streamer extending out to 4000 au can be characterized in a dual-band analysis. The dust properties are similar to those in the interstellar medium and imply a high dust mass. A massive streamer like this can affect the evolution of the star- and planet-forming inner system strongly. [ABSTRACT FROM AUTHOR]

Context. Three-dimensional (3D) kinetic maps of the Milky Way interstellar medium are an essential tool in studies of its structure and of star formation. Aims. We aim to assign radial velocities to Galactic interstellar clouds now spatially localized based on starlight extinction and star distances from Gaia and stellar surveys. Methods. We developed an automated search for coherent projections on the sky of clouds isolated in 3D extinction density maps on the one hand, and regions responsible for CO radio emissions at specific Doppler shifts on the other hand. The discrete dust structures were obtained by application of the Fellwalker algorithm to a recent 3D extinction density map. For each extinction cloud, a technique using a narrow sliding spectral window moved along the contour-bounded CO spectrum and geometrical criteria was used to select the most likely velocity interval. Results. We applied the new contour-based technique to the 3D extinction density distribution within the volume encompassing the Taurus, Auriga, Perseus, and California molecular complexes. From the 45 clouds issued from the decomposition, 42 were assigned a velocity. The remaining structures correspond to very weak CO emission or extinction. We used the non-automated assignments of radial velocities to clouds of the same region presented in Paper I and based on KI absorption spectra as a validation test. The new fully automated determinations were found to be in good agreement with these previous measurements. Conclusions. Our results show that an automated search based on cloud-contour morphology can be efficient and that this novel technique may be extended to wider regions of the Milky Way and at larger distance. We discuss its limitations and potential improvements after combination with other techniques. [ABSTRACT FROM AUTHOR]

We examine the physical conditions required for the formation of H2 in the solar neighborhood by comparing H i emission and absorption spectra toward 58 lines of sight at b < −5∘ to CO(1–0) and dust data. Our analysis of CO-associated cold and warm neutral medium (CNM and WNM) shows that the formation of CO-traced molecular gas is favored in regions with high column densities where the CNM becomes colder and more abundant. In addition, our comparison to the one-dimensional steady-state H i-to-H2 transition model of Bialy et al. (2016) suggests that only a small fraction of the clumpy CNM participates in the formation of CO-traced molecular gas. Another possible interpretation would be that missing physical and chemical processes in the model could play an important role in H2 formation. [ABSTRACT FROM AUTHOR]

We measured the extinction law in the 30 Dor star formation region in the Large Magellanic Cloud using Early Release Observations (EROs) taken with Near-Infrared Camera (NIRCam) on board the JWST, thereby extending previous studies carried out with the Hubble Space Telescope to the infrared. We used red clump stars to derive the direction of the reddening vector in twelve bands and we present the extinction law in this massive star forming region from 0.3 to 4.7 μm. At wavelengths longer than 1 μm, we find a ratio of total and selective extinction twice as high as in the diffuse Milky Way interstellar medium and a change in the relative slope from the optical to the infrared domain. Additionally, we derive an infrared extinction map and find that extinction closely follows the structure of the highly embedded regions of 30 Dor. [ABSTRACT FROM AUTHOR]

Context. The study of post-asymptotic giant branch (post-AGB) stars is a valuable tool in improving our understanding of poorly known aspects of the evolution of the stars throughout the asymptotic giant branch (AGB). This can be done thanks to the availability of more accurate determinations of their surface chemical composition and the peculiar shape of their spectral energy distribution (SED): the emission from the central star can be easily disentangled from the contribution from the dusty shell, which can then be characterized. Aims. The goal of the present study is to reconstruct the dust formation process and, more generally, the late phases of evolution for oxygen-rich stars across the AGB phase. This is performed by studying oxygen-rich, post-AGB stars and analyzing them in terms of their luminosity, effective temperature, and infrared excess. Methods. We studied sources classified as single, oxygen-rich, post-AGB stars in the Galaxy that exhibit a double-peaked (shell-type) SED. We used results from stellar evolution modeling, combined with dust formation and radiative transfer modeling, to reconstruct late AGB phases and the initial contraction to the post-AGB phase. We also determined the mass-loss and dust-formation rates for stars of different masses and chemical compositions. Results. The analysis of the IR excess of the post-AGB, oxygen-rich stars examined in this study outlines an interesting complexity with regard to the correlation between the dust in the surroundings of the stars, the evolutionary status, and the progenitor's mass. The sources descending from massive AGBs (> 3 M⊙, depending on metallicity) are generally characterized by higher infrared excess than the lower mass counterparts, owing to the more intense dust formation taking place during the final AGB phases. From the determination of the location of the dusty regions, we can deduce that the expanding velocities of the outflow change significantly from star to star. We also discuss the possibility that radiation pressure is not able of accelerating the wind in the faintest objects. [ABSTRACT FROM AUTHOR]

Context. Filamentary structures are an important part of star-forming interstellar clouds. The properties of filaments hold clues to their formation mechanisms and their role in the star-formation process. Aims. We compare the properties of filaments in the Orion Molecular Cloud 3 (OMC-3), as seen in mid-infrared (MIR) absorption and far-infrared (FIR) dust emission. We also wish to characterise some potential sources of systematic errors in filament studies. Methods. We calculated optical depth maps of the OMC-3 filaments based on the MIR absorption seen in Spitzer data and FIR dust emission observed with Berschel and the ArTéMiS instrument. We then compared the filament properties extracted from the data. Potential sources of error were investigated more generally with the help of radiative transfer models. Results. The widths of the selected OMC-3 filament segments are in the range 0.03–0.1 pc, with similar average values seen in both MIR and FIR analyses. Compared to the widths, the individual parameters of the fitted Plummer functions are much more uncertain. The asymptotic power-law index has typically values p ~ 3 but with a large scatter. Modelling shows that the FIR observations can systematically overestimate the filament widths. The effect is potentially tens of per cent at column densities above N(H2) ~ 1022 cm–2 but is reduced in more intense radiation fields, such as the Orion region. Spatial variations in dust properties could cause errors of similar magnitude. In the MIR analysis, dust scattering should generally not be a significant factor, unless there are high-mass stars nearby or the dust MIR scattering efficiency is higher than in the tested dust models. Thermal MIR dust emission can be a more significant source of error, especially close to embedded sources. Conclusions. The analysis of interstellar filaments can be affected by several sources of systematic error, but mainly at high column densities and, in the case of FIR observations, in weak radiation fields. The widths of the OMC-3 filaments were consistent between the MIR and FIR analyses and did not reveal any systematic dependence on the angular resolution of the observations. [ABSTRACT FROM AUTHOR]

Context. The Crab Nebula emits exceptionally bright non-thermal radiation across the entire wavelength range from the radio to the most energetic photons. So far, the underlying physical model of a relativistic wind from the pulsar terminating in a hydrodynamic standing shock has remained fairly unchanged since the early 1970s when it was first introduced. One of the predictions of this model is an increase in the toroidal magnetic field downstream from the shock where the flow velocity drops quickly with increasing distance until it reaches its asymptotic value, matching the expansion velocity of the nebula. Aims. The magnetic field strength in the nebula is poorly known. Using the recent measurements of the spatial extension and improved spectroscopy of the gamma-ray nebula, it has become –for the first time – feasible to determine in a robust way both the strength as well as the radial dependence of the magnetic field in the downstream flow. Methods. In this work, we introduce a detailed radiative model which was used to calculate the emission from non-thermal electrons (synchrotron and inverse Compton) as well as from thermal dust present in the Crab Nebula in a self-consistent way to compare it quantitatively with observational data. Special care was given to the radial dependence of the electron and seed field density. Results. The radiative model was used to estimate the parameters related to the electron populations responsible for radio and optical/X-ray synchrotron emission. In this context, the mass of cold and warm dust was determined. A combined fit based upon a χ2 minimisation successfully reproduced the complete data set used. For the best-fitting model, the energy density of the magnetic field dominates over the particle energy density up to a distance of ≈1.3 rs (rs: distance of the termination shock from the pulsar). The very high energy (VHE: E > 100 GeV) and ultra-high energy (UHE: E > 100 TeV) gamma-ray spectra set the strongest constraints on the radial dependence of the magnetic field, favouring a model where B(r) = (264 ± 9) μG(r/rs)−0.51 ± 0.03. For a collection of VHE measurements during epochs of higher hard X-ray emission, a significantly different solution B(r) = (167 ± 5) μG(r/rs)−0.29(+0.03, −0.06) is found. Conclusions. The high energy (HE: E > 100 MeV) and VHE gamma-ray observations of the Crab Nebula lift the degeneracy of the synchrotron emission between particle and magnetic field energy density. The reconstructed magnetic field and its radial dependence indicates a ratio of Poynting to kinetic energy flux σ ≈ 0.1 at the termination shock, which is ≈30 times larger than estimated up to now. Consequently, the confinement of the nebula would require additional mechanisms to slow the flow down through, for example, excitation of small-scale turbulence with possible dissipation of the magnetic field. [ABSTRACT FROM AUTHOR]

We present the first Bayesian method for tomographic decomposition of the plane-of-sky orientation of the magnetic field with the use of stellar polarimetry and distance. This standalone tomographic inversion method presents an important step forward in reconstructing the magnetized interstellar medium (ISM) in three dimensions within dusty regions. We develop a model in which the polarization signal from the magnetized and dusty ISM is described by thin layers at various distances, a working assumption which should be satisfied in small-angular circular apertures. Our modeling makes it possible to infer the mean polarization (amplitude and orientation) induced by individual dusty clouds and to account for the turbulence-induced scatter in a generic way. We present a likelihood function that explicitly accounts for uncertainties in polarization and parallax. We develop a framework for reconstructing the magnetized ISM through the maximization of the log-likelihood using a nested sampling method. We test our Bayesian inversion method on mock data, representative of the high Galactic latitude sky, taking into account realistic uncertainties from Gaia and as expected for the optical polarization survey PASIPHAE according to the currently planned observing strategy. We demonstrate that our method is effective at recovering the cloud properties as soon as the polarization induced by a cloud to its background stars is higher than ~0.1% for the adopted survey exposure time and level of systematic uncertainty. The larger the induced polarization is, the better the method's performance, and the lower the number of required stars. Our method makes it possible to recover not only the mean polarization properties but also to characterize the intrinsic scatter, thus creating new ways to characterize ISM turbulence and the magnetic field strength. Finally, we apply our method to an existing data set of starlight polarization with known line-of-sight decomposition, demonstrating agreement with previous results and an improved quantification of uncertainties in cloud properties. [ABSTRACT FROM AUTHOR]

Large fractions of metals are missing from the observable gas-phase in the interstellar medium (ISM) because they are incorporated into dust grains. This phenomenon is called dust depletion. It is important to study the depletion of metals into dust grains in the ISM to investigate the origin and evolution of metals and cosmic dust. We characterize the dust depletion of several metals from the Milky Way to distant galaxies. We collected measurements of ISM metal column densities from absorption-line spectroscopy in the literature, and in addition, we determined Ti and Ni column densities from a sample of 70 damped Lyman-α absorbers (DLAs) toward quasars that were observed at high spectral resolution with the Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). We used relative ISM abundances to estimate the dust depletion of 18 metals (C, P, O, Cl, Kr, S, Ge, Mg, Si, Cu, Co, Mn, Cr, Ni, Al, Ti, Zn, and Fe) for different environments (the Milky Way, the Magellanic Clouds, and DLAs toward quasars and towards gamma-ray bursts). We observed overall linear relations between the depletion of each metal and the overall strength of the dust depletion, which we traced with the observed [Zn/Fe]. The slope of these dust depletion sequences correlates with the condensation temperature of the various elements, that is, the more refractory elements show steeper depletion sequences. In the neutral ISM of the Magellanic Clouds, small deviations from linearity are observed as an overabundance of the α-elements Ti, Mg, S, and an underabundance of Mn, including for metal-rich systems. The Ti, Mg, and Mn deviations completely disappear when we assume that all systems in our sample of OB stars observed toward the Magellanic Clouds have an α-element enhancement and Mn underabundance, regardless of their metallicity. This may imply that the Magellanic Clouds have recently been enriched in α-elements, potentially through recent bursts of star formation. We also observe an S overabundance in all local galaxies, which is an effect of ionization due to the contribution of their H ii regions to the measured S ii column densities. The observed strong correlations of the depletion sequences of the metals all the way from low-metallicity quasi-stellar object DLAs to the Milky Way suggest that cosmic dust has a common origin, regardless of the star formation history, which, in contrast, varies significantly between these different galaxies. This supports the importance of grain growth in the ISM as a significant process of dust production. [ABSTRACT FROM AUTHOR]

Context. Nano-diamonds are an enticing and enigmatic dust component yet their origin is still unclear. They have been unequivocally detected in only a few astronomical objects, yet they are the most abundant of the pre-solar grains, both in terms of mass and number. Aims. Our goal is to derive a viable set of nano-diamond optical constants and optical properties to enable their modelling in any type of astrophysical object where, primarily, the local (inter)stellar radiation field is well-determined. Methods. The complex indices of refraction, m(n, k), of nano-diamonds, constrained by available laboratory measurements, were calculated as a function of size, surface hydrogenation, and internal (dis)order, using the THEMIS a-C(:H) methodology optEC(s)(a). Results. To demonstrate the utility of the optical properties (the efficiency factors Qext, Qsca, and Qabs), calculated using the derived m(n, k) data, we show that nano-diamonds could be abundant in the interstellar medium (ISM) and yet remain undetectable there. Conclusions. The derived optical constants provide a means to explore the existence and viability of nano-diamonds in a wide range of astronomical sources. Here we show that up to a few percent of the available carbon budget could be hidden in the form of nano-diamonds in the diffuse ISM, in abundances comparable to the pre-solar nano-diamond abundances in primitive meteorites. [ABSTRACT FROM AUTHOR]

Context. Nano-diamonds have been observed in only a handful of circumstellar regions 10–100 au from moderately bright stars (Teff ~ 8000–10 000 K). They have also been extracted from primitive meteorites; some of these are clearly pre-solar, that is to say that they formed far from the solar system and therefore traversed the interstellar medium, where they must exist but, because we see no evidence of them, must be extremely well hidden. Aims. Our goal is to understand if it is possible to constrain the sizes and shapes of nano-diamonds in circumstellar media using the observed ratio, [CH]/[CH2], of their surface CH2 and CH infrared bands at ≃3.43 μm and ≃3.53 μm, respectively. Methods. We calculated the CH and CH2 abundances on nano-diamonds using two approaches. The first assumes regular and semi-regular polyhedra (tetrahedra, octahedra, and cubes and their truncated forms). The second uses a diamond bonding network to derive the structures of tetrahedral and octahedral particles, and their truncated variants, and also of spherical nano-diamonds. Results. As a function of the particle size and shape, and for the two different calculation methods, we derived the relative abundance ratio [CH]/[CH2], which can then be weighted by their laboratory-measured infrared band intensities. The two methods give good agreement and indicate that the spread in values, over the different particle forms, is more that an order of magnitude for any size. Conclusions. We conclude that the ratio [CH]/[CH2], and their infrared band ratio, strongly depend upon particle size and shape. For a given shape or size, the ratio can vary by more than an order of magnitude. It may therefore be difficult to constrain nano-diamond sizes using the observed 3–4 μm spectra alone. James Webb Space Telescope mid-infrared spectra may help, but only if bands are size-specific. [ABSTRACT FROM AUTHOR]

Coagulation driven by supersonic turbulence is primarily an astrophysical problem because coagulation processes on Earth are normally associated with incompressible fluid flows at low Mach numbers, while dust aggregation in the interstellar medium for instance is an example of the opposite regime. We study coagulation of inertial particles in compressible turbulence using high-resolution direct and shock-capturing numerical simulations with a wide range of Mach numbers from nearly incompressible to moderately supersonic. The particle dynamics is simulated by representative particles and the effects on the size distribution and coagulation rate due to increasing Mach number is explored. We show that the time evolution of particle size distribution mainly depends on the compressibility (Mach number). We find that the average coagulation kernel ⟨Cij⟩ scales linearly with the average Mach number ℳrms multiplied by the combined size of the colliding particles, that is, 〈Cij〉∼〈(ai+aj)3〉 ℳrmsτη−1 〈 C i j 〉 ∼ 〈 (a i + a j) 3 〉 M rms τ η − 1 $ \langle C_{ij}\rangle \sim \langle (a_i + a_j)^3\rangle\, \mathcal{M}_{\rm rms}\tau_\eta^{-1} $ , which is qualitatively consistent with expectations from analytical estimates. A quantitative correction 〈Cij〉∼〈(ai+aj)3〉(vp,rms/cs)τη−1 〈 C i j 〉 ∼ 〈 (a i + a j) 3 〉 (v p , rms / c s) τ η − 1 $ \langle C_{ij}\rangle \sim \langle(a_i + a_j)^3\rangle({\it v}_{\rm p,rms}/c_{\rm s})\tau_\eta^{-1} $ is proposed and can serve as a benchmark for future studies. We argue that the coagulation rate ⟨Rc⟩ is also enhanced by compressibility-induced compaction of particles. [ABSTRACT FROM AUTHOR]

Aims. We study the growth of dust in oxygen-rich stellar outflows in order to find out to which extent dust growth models can quantitatively reconcile with the quantities and nature of dust as derived from observations of the infrared emission from circumstellar dust shells. Methods. We use a set of nine well-observed massive supergiants with optically thin dust shells as testbeds because of the relatively simple properties of the outflows from massive supergiants, contrary to the case of AGB stars. Models of the infrared emission from their circumstellar dust shells are compared to their observed infrared spectra to derive the essential parameters that rule dust formation in the extended envelope of these stars. The results are compared with a model for silicate dust condensation. Results. For all objects, the infrared emission in the studied wavelength range, between 6 and 25 μm, can be reproduced rather well by a mixture of non-stoichiometric iron-bearing silicates, alumina, and metallic iron dust particles. For three objects (μ Cep, RW Cyg, and RS Per), the observed spectra can be sufficiently well reproduced by a stationary and (essentially) spherically symmetric outflow in the instantaneous condensation approximation. For these objects, the temperature at the onset of massive silicate dust growth is of the order of 920 K and the corresponding outflow velocity of the order of the sound velocity. This condensation temperature is only somewhat below the vapourisation temperature of the silicate dust and suggests that the silicate dust grows on the corundum dust grains that formed well inside of the silicate dust shell at a much higher temperature. The low expansion velocity at the inner edge of the silicate dust shell further suggests that, for these supergiants, the region inside the silicate dust shell has an only subsonic average expansion velocity, though a high degree of supersonic turbulence is indicated by the widths of spectral lines. Conclusions. Our results suggest that for the two major problems of dust formation in stellar outflows, that is (i) formation of seed nuclei and (ii) their growth to macroscopic dust grains, we are gradually coming close to a quantitative understanding of the second item. [ABSTRACT FROM AUTHOR]

The ubiquitous presence of Galactic cirri in deep optical images represents a major obstacle to study the low surface brightness features of extragalactic sources. To address this issue, we have explored the optical properties of cirri using g, r, i, and z bands in the Sloan Digital Sky Survey (SDSS) Stripe82 region. Using state-of-the-art, custom made, image processing techniques, including the modeling and removal of the instrumental scattered light produced by the stars, we managed to isolate the optical diffuse emission by the cirri, allowing their photometric characterization. We find that their optical colors are driven by the dust column density: The cirri become redder as their 100 μm emission increases. Remarkably, the optical colors of the Galactic cirri differ significantly from those of extragalactic sources, with a characteristic bluer r-i color for a given g-r, allowing one to detect these by using a simple color relation. Our results show the high potential of deep multi-band optical photometry, on its own, identifying the presence of cirri at a higher spatial resolution than those provided by far-infrared observations. The combination of very deep data and multi-band photometry (as the one produced by LSST and Euclid) would make it possible to build dust maps of unprecedented quality. [ABSTRACT FROM AUTHOR]

The evaporation of molecules from dust grains is crucial to understanding some key aspects of the star- and the planet-formation processes. During the heating phase, the presence of young protostellar objects induces molecules to evaporate from the dust surface into the gas phase, enhancing its chemical complexity. Similarly, in circumstellar discs, the position of the so-called snow lines is determined by evaporation, with important consequences for the formation of planets. The amount of molecules that are desorbed depends on the interaction between the species and the grain surface, which is controlled by the binding energy. Recent theoretical and experimental works point towards a distribution of values for this parameter instead of the single value often employed in astrochemical models.We present a new "multi-binding energy" framework to assess the effects that a distribution of binding energies has on the amount of species bound to the grains. We find that the efficiency of the surface chemistry is significantly influenced by this process, with crucial consequences on the theoretical estimates of the desorbed species. [ABSTRACT FROM AUTHOR]

Context. Investigating the dust heating mechanisms in galaxies provides a deeper understanding of how the internal energy balance drives their evolution. Over the last decade radiative transfer simulations based on the Monte Carlo method have emphasised the role of the various stellar populations heating the diffuse dust. Beyond the expected heating through ongoing star formation, older stellar populations (≥8 Gyr) and even active galactic nuclei can both contribute energy to the infrared emission of diffuse dust. Aims. In this particular study we examine how the radiation of an external heating source, such as the less massive galaxy NGC 5195 in the M 51 interacting system, could affect the heating of the diffuse dust of its parent galaxy NGC 5194, and vice versa. Our goal is to quantify the exchange of energy between the two galaxies by mapping the 3D distribution of their radiation field. Methods. We used SKIRT, a state-of-the-art 3D Monte Carlo radiative transfer code, to construct the 3D model of the radiation field of M 51, following the methodology defined in the DustPedia framework. In the interest of modelling, the assumed centre-to-centre distance separation between the two galaxies is ∼10 kpc. Results. Our model is able to reproduce the global spectral energy distribution of the system, and it matches the resolved optical and infrared images fairly well. In total, 40.7% of the intrinsic stellar radiation of the combined system is absorbed by dust. Furthermore, we quantify the contribution of the various dust heating sources in the system, and find that the young stellar population of NGC 5194 is the predominant dust-heating agent, with a global heating fraction of 71.2%. Another 23% is provided by the older stellar population of the same galaxy, while the remaining 5.8% has its origin in NGC 5195. Locally, we find that the regions of NGC 5194 closer to NGC 5195 are significantly affected by the radiation field of the latter, with the absorbed energy fraction rising up to 38%. The contribution of NGC 5195 remains under the percentage level in the outskirts of the disc of NGC 5194. This is the first time that the heating of the diffuse dust by a companion galaxy is quantified in a nearby interacting system. [ABSTRACT FROM AUTHOR]

The unprecedented astrometry from Gaia's second data release (DR2) provides us with an opportunity to study molecular clouds in the solar neighbourhood in detail. Extracting the wealth of information in these data remains a challenge, however. We have further improved our Gaussian-processes-based, three-dimensional dust mapping technique to allow us to study molecular clouds in more detail. These improvements include a significantly better scaling of the computational cost with the number of stars, and taking into account distance uncertainties to individual stars. Using Gaia DR2 astrometry together with the Two Micron All Sky Survey (2MASS) and the Wide-Field Infrared Survey Explorer (WISE) photometry for 30 000 stars, we infer the distribution of dust out to 600 pc in the direction of the Orion A molecular cloud. We identify a bubble-like structure in front of Orion A, centred at a distance of about 350 pc from the Sun. The main Orion A structure is visible at slightly larger distances, and we clearly see a tail extending over 100 pc that is curved and slightly inclined to the line of sight. The location of our foreground structure coincides with 5–10 Myr old stellar populations, suggesting a star formation episode that predates that of the Orion Nebula Cluster itself. We also identify the main structure of the Orion B molecular cloud, and in addition discover a background component to this at a distance of about 460 pc from the Sun. Finally, we associate our dust components at different distances with the plane-of-the-sky magnetic field orientation as mapped by Planck. This provides valuable information for modelling the magnetic field in three dimensions around star-forming regions. [ABSTRACT FROM AUTHOR]

Context. LDN 1642 is a rare example of a star-forming, high-latitude molecular cloud. The dust emission of LDN 1642 has already been studied extensively in the past, but its location also makes it a good target for studies of light scattering. Aims. We wish to study the near-infrared (NIR) light scattering in LDN 1642, its correlation with the cloud structure, and the ability of dust models to simultaneously explain observations of sub-millimetre dust emission, NIR extinction, and NIR scattering. Methods. We used observations made with the HAWK-I instrument to measure the NIR surface brightness and extinction in LDN 1642. These data were compared with Herschel observations of dust emission and, with the help of radiative transfer modelling, with the predictions calculated for different dust models. Results. We find, for LDN 1642, an optical depth ratio τ(250 μm)∕τ(J) ≈ 10−3, confirming earlier findings of enhanced sub-millimetre emissivity. The relationships between the column density derived from dust emission and the NIR colour excesses are linear and consistent with the shape of the standard NIR extinction curve. The extinction peaks at AJ = 2.6 mag, and the NIR surface brightness remains correlated with N(H2) without saturation. Radiative transfer models are able to fit the sub-millimetre data with any of the tested dust models. However, these predict an NIR extinction that is higher and an NIR surface brightness that is lower than based on NIR observations. If the dust sub-millimetre emissivity is rescaled to the observed value of τ(250 μm)∕τ(J), dust models with high NIR albedo can reach the observed level of NIR surface brightness. The NIR extinction of the models tends to be higher than in the direct extinction measurements, which is also reflected in the shape of the NIR surface brightness spectra. Conclusions. The combination of emission, extinction, and scattering measurements provides strong constraints on dust models. The observations of LDN 1642 indicate clear dust evolution, including a strong increase in the sub-millimetre emissivity, which has not been fully explained by the current dust models yet. [ABSTRACT FROM AUTHOR]

Context. The early-type galaxy NGC 1316, associated with the radio source Fornax A, hosts about 107 M⊙ of dust within a central radius of 5 kpc. These prominent dust structures are believed to have an external origin, which is also a popular interpretation for other dusty early-type galaxies. Moreover, it has been long known that ionised gas is present in NGC 1316, but to date there has been a lack of detailed investigation. Aims. Our aim is to understand the nature of ionised gas and dust in NGC 1316 and to offer an interpretation for the origin of the dust. Methods. We use archival Hubble Space Telescope/Advanced Camera for Surveys data to construct colour maps that delineate the dust pattern in detail, and we compare these data with maps constructed with data from the Multi Unit Spectroscopic Explorer (MUSE) instrument of the Very Large Telescope at the European Southern Observatory. Twelve MUSE pointings in wide field mode form a mosaic of the central 3.3 × 2.4 arcmin2. We use the tool PyParadise to fit the stellar population. We use the residual emission lines and the residual interstellar absorption NaI D-lines, and we measure line strengths, the velocity field, and the velocity dispersion field. Results. The emission lines resemble low-ionisation nuclear emission-line region lines, with [NII] being the strongest line everywhere. Ionising sources are plausibly the post-asymptotic giant branch stars of the old or intermediate-age stellar population. There is a striking match between the dust structures, ionised gas, and atomic gas distributions, the last of which is manifested by interstellar absorption residuals of the stellar NaI D-lines. In the dust-free regions, the interstellar NaI D-lines appear in emission, which is indicative of a galactic wind. The velocity field of the ionised gas (and thus of the dust) is characterised by small-scale turbulent movements that indicate short lifetimes. At the very centre, a bipolar velocity field of the ionised gas is observed, which we interpret as an outflow. The low-velocity part is associated with dust. We identify a strongly inclined gaseous dusty disc along the major axis of NGC 1316. A straight beam of ionised gas with a length of about 4 kpc emanates from the centre. Conclusions. The dust in NGC 1316 has different origins. Our findings are strongly suggestive of a dusty outflow that is curved along the line-of-sight. Nuclear outflows may be important dust-producing machines in galaxies. Another dusty gaseous component forms a disc that we identify as the predecessor of a central dust lane. [ABSTRACT FROM AUTHOR]

Context. The degree of coupling between the gas and the magnetic field during the collapse of a core and the subsequent formation of a disk depends on the assumed dust size distribution. Aims. We study the impact of grain–grain coagulation on the evolution of magnetohydrodynamic (MHD) resistivities during the collapse of a prestellar core. Methods. We use a 1D model to follow the evolution of the dust size distribution, out-of-equilibrium ionisation state, and gas chemistry during the collapse of a prestellar core. To compute the grain–grain collisional rate, we consider models for both random and systematic, size-dependent, velocities. We include grain growth through grain–grain coagulation and ice accretion, but ignore grain fragmentation. Results. Starting with a Mathis-Rumpl-Nordsieck (MRN) size distribution (Mathis et al. 1977, ApJ, 217, 425), we find that coagulation in grain–grain collisions generated by hydrodynamical turbulence is not efficient at removing the smallest grains and, as a consequence, does not have a large effect on the evolution of the Hall and ambipolar diffusion MHD resistivities, which still drop significantly during the collapse like in models without coagulation. The inclusion of systematic velocities, possibly induced by the presence of ambipolar diffusion, increases the coagulation rate between small and large grains, removing small grains earlier in the collapse and therefore limiting the drop in the Hall and ambipolar diffusion resistivities. At intermediate densities (nH ~ 108 cm−3), the Hall and ambipolar diffusion resistivities are found to be higher by 1 to 2 orders of magnitude in models with coagulation than in models where coagulation is ignored, and also higher than in a toy model without coagulation where all grains smaller than 0.1 μm would have been removed in the parent cloud before the collapse. Conclusions. When grain drift velocities induced by ambipolar diffusion are included, dust coagulation happening during the collapse of a prestellar core starting from an initial MRN dust size distribution appears to be efficient enough to increase the MHD resistivities to the values necessary to strongly modify the magnetically regulated formation of a planet-forming disk. A consistent treatment of the competition between fragmentation and coagulation is, however, necessary before reaching firm conclusions. [ABSTRACT FROM AUTHOR]

Aims. We tackle the conundrums of organic materials missing from interstellar dust when measured inside the Solar System, while undoubtedly existing in the local interstellar cloud (LIC), which surrounds the Solar System. Methods. We present a theoretical argument that organic compounds sublimate almost instantaneously by exothermic reactions, when solar insolation triggers the recombination of free radicals or the rearrangement of carbon bonds in the compounds. Results. It turns out that the triggering temperature lies in the range of 20–50 K by considering that sublimation of organic materials takes place beyond the so-called filtration region of interstellar neutral atoms. We find that in-situ measurements of LIC dust in the Solar System result in an overestimate for the gas-to-dust mass ratio of the LIC, unless the sublimation of organic materials is taken into account. We also find that previous measurements of interstellar pickup ions have determined the total elemental abundances of gas and organic materials, instead of interstellar gas alone. Conclusions. We conclude that LIC organic matter suffers from sublimation en route to the heliosphere, implying that our understanding of LIC dust from space missions is incomplete. Since space missions inside the orbit of Saturn cannot give any information on the organic substances of LIC dust, one must await a future exploration mission to the inner edge of the Oort cloud for a thorough understanding of organic substances in the LIC. Once our model for the sublimation of interstellar organic matter by exothermic chemical reactions of free radicals is confirmed, the hypothesis of panspermia from the diffuse interstellar medium is ruled out. [ABSTRACT FROM AUTHOR]

Interstellar dust permeates our Galaxy and plays an important role in many physical processes in the diffuse and dense regions of the interstellar medium (ISM). High-resolution X-ray spectroscopy, coupled with modelling based on laboratory dust measurements, provides a unique probe for investigating the interstellar dust properties along our line of sight towards Galactic X-ray sources. Here, we focus on the oxygen content of the ISM through its absorption features in the X-ray spectra. To model the dust features, we perform a laboratory experiment using the electron microscope facility located at the University of Cadiz in Spain, where we acquire new laboratory data in the oxygen K-edge. We study 18 dust samples of silicates and oxides with different chemical compositions. The laboratory measurements are adopted for our astronomical data analysis. We carry out a case study on the X-ray spectrum of the bright low-mass X-ray binary Cygnus X-2, observed by XMM−Newton. We determine different temperature phases of the ISM and parameterise oxygen in both gas (neutral and ionised) and dust form. We find Solar abundances of oxygen along the line of sight towards the source. Due to both the relatively low depletion of oxygen into dust form and the shape of the oxygen cross section profiles, it is challenging to determine the precise chemistry of interstellar dust. However, silicates provide an acceptable fit. Finally, we discuss the systematic discrepancies in the atomic (gaseous phase) data of the oxygen edge spectral region using different X-ray atomic databases as well as consider future prospects for studying the ISM with the Arcus concept mission. [ABSTRACT FROM AUTHOR]

The statistical characterization of the diffuse magnetized interstellar medium (ISM) and Galactic foregrounds to the cosmic microwave background (CMB) poses a major challenge. To account for their non-Gaussian statistics, we need a data analysis approach capable of efficiently quantifying statistical couplings across scales. This information is encoded in the data, but most of it is lost when using conventional tools, such as one-point statistics and power spectra. The wavelet scattering transform (WST), a low-variance statistical descriptor of non-Gaussian processes introduced in data science, opens a path towards this goal. To establish the methodology, we applied the WST to noise-free maps of dust polarized thermal emission computed from a numerical simulation of magnetohydrodynamical turbulence in the diffuse ISM. We analyzed normalized complex Stokes maps and maps of the polarization fraction and polarization angle. The WST yields a few thousand coefficients; some of them measure the amplitude of the signal at a given scale, and the others characterize the couplings between scales and orientations. The dependence on orientation can be fitted with the reduced wavelet scattering transform (RWST), an angular model introduced in previous works for total intensity maps. The RWST provides a statistical description of the polarization maps, quantifying their multiscale properties in terms of isotropic and anisotropic contributions. It allowed us to exhibit the dependence of the map structure on the orientation of the mean magnetic field and to quantify the non-Gaussianity of the data. We also used RWST coefficients, complemented by additional constraints, to generate random synthetic maps with similar statistics. Their agreement with the original maps demonstrates the comprehensiveness of the statistical description provided by the RWST. This work is a step forward in the analysis of observational data and the modeling of CMB foregrounds. We also release PyWST, a public Python package to perform WST and RWST analyses of two-dimensional data. [ABSTRACT FROM AUTHOR]

Context. Dense molecular filaments are central to the star formation process, but the detailed manner in which they fragment into prestellar cores is not well understood yet. Aims. Here, we investigate the fragmentation properties and dynamical state of several star-forming filaments in the X-shaped nebula region of the California molecular cloud in an effort to shed some light on this issue. Methods. We used multiwavelength far-infrared images from Herschel as well as the getsources and getfilaments extraction methods to identify dense cores and filaments in the region and derive their basic properties. We also used a map of 13CO(2−1) emission from the Arizona 10m Submillimeter Telescope (SMT) to constrain the dynamical state of the filaments. Results. We identified ten filaments with aspect ratios of AR > 4 and column density contrasts of C > 0.5, as well as 57 dense cores, including two protostellar cores, 20 robust prestellar cores, 11 candidate prestellar cores, and 24 unbound starless cores. All ten filaments have roughly the same deconvolved full width at half maximum (FWHM), with a median value of 0.12 ± 0.03 pc, which is independent of their column densities ranging from <1021 cm−2 to >1022 cm−2. Two star-forming filaments (# 8 and # 10) stand out since they harbor quasi-periodic chains of dense cores with a typical projected core spacing of ~0.15 pc. These two filaments have thermally supercritical line masses and are not static. Filament 8 exhibits a prominent transverse velocity gradient, suggesting that it is accreting gas from the parent cloud gas reservoir at an estimated rate of ~40 ± 10 M⊙ Myr−1 pc−1. Filament 10 includes two embedded protostars with outflows and it is likely at a somewhat later evolutionary stage than filament 8. In both cases, the observed (projected) core spacing is similar to the filament width and significantly shorter than the canonical separation of ~4 times the filament width predicted by classical cylinder fragmentation theory. It is unlikely that projection effects can explain this discrepancy. We suggest that the continuous accretion of gas onto the two star-forming filaments, as well as the geometrical bending of the filaments, may account for the observed core spacing. Conclusions. Our findings suggest that the characteristic fragmentation lengthscale of molecular filaments is quite sensitive to external perturbations from the parent cloud, such as the gravitational accretion of ambient material. [ABSTRACT FROM AUTHOR]

The ρ Oph molecular cloud is one of the best examples of spinning dust emission, first detected by the cosmic background imager (CBI). Here, we present 4.5 arcmin observations with CBI 2 that confirm 31 GHz emission from ρ Oph W, the PDR exposed to B-type star HD 147889, and highlight the absence of signal from S1, the brightest IR nebula in the complex. In order to quantify an association with dust-related emission mechanisms, we calculated correlations at different angular resolutions between the 31 GHz map and proxies for the column density of IR emitters, dust radiance, and optical depth templates. We found that the 31 GHz emission correlates best with the PAH column density tracers, while the correlation with the dust radiance improves when considering emission that is more extended (from the shorter baselines), suggesting that the angular resolution of the observations affects the correlation results. A proxy for the spinning dust emissivity reveals large variations within the complex, with a dynamic range of 25 at 3σ and a variation by a factor of at least 23, at 3σ, between the peak in ρ Oph W and the location of S1, which means that environmental factors are responsible for boosting spinning dust emissivities locally. [ABSTRACT FROM AUTHOR]

Molecular emission lines are essential tools to shed light on many questions regarding star formation in galaxies. Multiple molecular lines are particularly useful to probe different phases of star-forming molecular clouds. In this study, we investigate the physical properties of giant molecular clouds (GMCs) using multiple lines of CO, i.e. CO(1–0, 2–1, 3–2) and 13CO(1–0), obtained at selected 20 positions in the disc of NGC 0628. A total of 11 positions were selected over the radial cut, including the centre, and remaining 9 positions were selected across the southern and northern arms of the galaxy. A total of 13 out of 20 positions are brighter at $24\, \mu {\rm m}$ and ultraviolet (UV) emission and hosting significantly more H ii regions compared to the rest of the positions indicating opposite characteristics. Our line ratio analysis shows that the gas gets warmer and thinner as a function of radius from the galaxy centre up to 1.7 kpc, and then the ratios start to fluctuate. Our empirical and model results suggest that the UV-bright positions have colder and thinner CO gas with higher hydrogen and CO column densities. However, the UV-dim positions have relatively warmer CO gas with lower densities bathed in GMCs surrounded by less number of H ii regions. Analysis of multiwavelength infrared and UV data indicates that the UV-bright positions have higher star formation efficiency than that of the UV-dim positions. [ABSTRACT FROM AUTHOR]

We consider a dusty clump in two cases of spherical and cylindrical symmetry to investigate the effect of temperature and density gradients on the observed flux density. Conversely, we evaluate how the presence of these gradients affects the calculation of the clump mass from the observed flux. We provide approximate expressions relating flux density and mass in the optically thick and thin limits and in the Rayleigh-Jeans regime, and we discuss the reliability of these expressions by comparing them to the outcome of a numerical code. Finally, we present the application of our calculations to three examples taken from the literature, which shows how the correction introduced after taking into account temperature and density gradients may affect our conclusions on the stability of the clumps. [ABSTRACT FROM AUTHOR]

Context. The size and chemical composition of interstellar dust grains are critical in setting the dynamical, physical, and chemical evolution of all the media in which they are present. Thanks to facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA) and, in the future, the Square Kilometer Array (SKA), thermal emission in the (sub)millimetre to centimetre domain has become a very convenient way to trace grain properties. Aims. Our aim is to understand the influence of the composition and size distribution of dust grains on the shape of their spectral energy distribution (peak position, spectral index) in dense interstellar regions such as molecular clouds, prestellar cores, young stellar objects, and protoplanetary discs. Methods. Starting from the optical constants defined in The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS) for amorphous hydrogenated carbon grains and amorphous silicates in addition to water ice, we defined six material mixtures that we believe are representative of the expected dust composition in dense interstellar regions. The optical properties of 0.01 μm to 10 cm grains were then calculated with effective medium and Mie theories. The corresponding spectral energy distributions were subsequently calculated for isolated clouds either externally heated by the standard interstellar radiation field alone or in addition to an internal source. Results. The three main outcomes of this study are as follows. Firstly, the dust mass absorption coefficient strongly depends on both grain composition and size distribution potentially leading to errors in dust mass estimates by factors up to ~3 and 20, respectively. Secondly, it appears almost impossible to retrieve the grain composition from the (sub)millimetre to centimetre thermal emission shape alone as its spectral index for λ ≳ 3 mm does not depend on dust composition. Thirdly, using the "true" dust opacity spectral index to estimate grain sizes may lead to erroneous findings as the observed spectral index can be highly modified by the dust temperature distribution along the line of sight, which depends on the specific heating source and on the geometry of the studied interstellar region. Conclusions. Based on the interpretation of only the spectral shape of (sub)millimetre to centimetre observational data, the determination of the dust masses, compositions, and sizes are highly uncertain. [ABSTRACT FROM AUTHOR]

Context. The interstellar bubble RCW 120 seen around a type O runaway star is driven by the stellar wind and the ionising radiation emitted by the star. The boundary between the stellar wind and interstellar medium (ISM) is associated with the arc-shaped mid-infrared dust emission around the star within the HII region. Aims. We aim to investigate the arc-shaped bow shock in RCW 120 by means of numerical simulations, including the radiation, dust, HII region, and wind bubble. Methods. We performed 3D radiation-hydrodynamic simulations including dust using the GUACHO code. Our model includes a detailed treatment of dust grains in the ISM and takes into account the drag forces between dust and gas and the effect of radiation pressure on the gas and dust. The dust is treated as a pressureless gas component. The simulation uses typical properties of RCW 120. We analyse five simulations to deduce the effect of the ionising radiation and dust on both the emission intensity and the shape of the shock. Results. The interaction of the wind and the ionising radiation from a runaway star with the ISM forms an arc-shaped bow shock where the dust from the ISM accumulates in front of the moving star. Moreover, the dust forms a second small arc-shaped structure within the rarefied region at the back of the star inside the bubble. In order to obtain the decoupling between the gas and the dust, it is necessary to include the radiation-hydrodynamic equations together with the dust and the stellar motion. In this work all these elements are considered together, and we show that the decoupling between gas and dust obtained in the simulation is in agreement with the morphology of the infrared observations of RCW 120. [ABSTRACT FROM AUTHOR]

Aims. Highly resolved maps of the local Galactic dust are an important ingredient for sky emission models. Over almost the whole electromagnetic spectrum one can see imprints of dust, many of which originate from dust clouds within 300 pc. Having a detailed 3D reconstruction of these local dust clouds enables detailed studies, helps to quantify the impact on other observables, and is a necessary milestone of larger reconstructions, as every sightline for more distant objects will pass through the local dust. Methods. To infer the dust density we use parallax and extinction estimates published by the Gaia collaboration in their second data release (DR2). We model the dust as a log-normal process using a hierarchical Bayesian model. We also nonparametrically infer the kernel of the log-normal process, which corresponds to the physical spatial correlation power spectrum of the log-density. Results. Using only data from Gaia DR2, we reconstruct the 3D dust density and its spatial correlation spectrum in a 600 pc cube centered on the Sun. We report a spectral index of the logarithmic dust density of 3.1 on Fourier scales with wavelengths between 2 and 125 pc. The resulting 3D dust map as well as the power spectrum and posterior samples are publicly available for download. [ABSTRACT FROM AUTHOR]

Context. The all-sky survey run by the Galaxy Evolution Explorer (GALEX AIS) mapped about 85% of the Galaxy at ultraviolet (UV) wavelengths and detected the diffuse UV background produced by the scattering of the radiation from OBA stars by interstellar dust grains. Against this background, diffuse weak structures were detected as well as the UV counterparts to nebulae and molecular clouds. Aims. To make full profit of the survey, unsupervised and semi-supervised procedures need to be implemented. The main objective of this work is to implement and analyze the results of the method developed by us for the blind detection of ISM features in the GALEX AIS. Methods. Most ISM features are detected at very low signal levels (dark filaments, globules) against the already faint UV background. We have defined an index, the UV background fluctuations index (or UBF index), to identify areas of the sky where these fluctuations are detected. The algorithm is applied to the images obtained in the far-UV (1344–1786 Å) band since this is less polluted by stellar sources, facilitating the automated detection. Results. The UBF index is shown to be sensitive to the main star forming regions within the Gould's Belt, and to some prominent loops like Loop I or the Eridanus and Monogem areas. The catalog with the UBF index values is made available online to the community. [ABSTRACT FROM AUTHOR]