Recent analyses of ${\it Herschel}$ observations suggest that in nearby disc galaxies the dust mass opacity at $500 \, {\rm μm}$, $κ_{500}$, decreases with increasing gas surface density, $Σ_{\rm ISM}$ (Clark et al. 2019). This apparent anti-correlation between $κ_{500}$ and $Σ_{\rm ISM}$ is opposite to the behaviour expected from theoretical dust evolution models; in such models, dust in denser, cooler regions (i.e. regions of increased $Σ_{\rm ISM}$) tends to grow and therefore to have increased $κ_{500}$. We show, using a toy model, that the presence of a range of dust temperatures along the line of sight can lead to spuriously low estimated values of $κ_{500}$. If in regions of higher $Σ_{\rm ISM}$ the range of dust temperatures extends to lower values (as seems likely), the magnitude of this effect may be sufficient to explain the apparent anti-correlation between $κ_{500}$ and $Σ_{\rm ISM}$. Therefore there may not be any need for spatial variation in the intrinsic dust properties that run counter to theoretical expectations.
We compare the performance of several dust models in reproducing the dust spectral energy distribution (SED) per unit extinction in the diffuse interstellar medium (ISM). We use our results to constrain the variability of the optical properties of big grains in the diffuse ISM, as published by the Planck collaboration. We use two different techniques to compare the predictions of dust models to data from the Planck HFI, IRAS and SDSS surveys. First, we fit the far-infrared emission spectrum to recover the dust extinction and the intensity of the interstellar radiation field (ISRF). Second, we …
3D tomography of the interstellar dust and gas may be useful in many respects, from the physical and chemical evolution of the ISM itself to foreground decontamination of the CMB, or various studies of the environments of specific objects. Our goal here is to bring more precise information on the distance to nearby interstellar dust and gas clouds within 250 pc. We apply the best available calibration methods to a carefully screened set of stellar Stromgren photometry data for targets possessing a Hipparcos parallax and spectral type classification. We combine the derived interstellar extincti…
We examine a model for the variable free-free and neutral hydrogen absorption inferred towards the cores of some compact radio galaxies in which a spatially fluctuating medium drifts in front of the source. We relate the absorption-induced intensity fluctuations to the statistics of the underlying opacity fluctuations. We investigate models in which the absorbing medium consists of either discrete clouds or a power-law spectrum of opacity fluctuations. We examine the variability characteristics of a medium comprised of Gaussian-shaped clouds in which the neutral and ionized matter are co-locat…
The thermal emission of dust is one of the most important tracers of the interstellar medium: multi-wavelength photometry in the far-infrared (FIR) and submillimeter (submm) can be fitted with a model, providing estimates of the dust mass. The fit results depend on the assumed value for FIR/submm opacity, which in most models - due to the scarcity, until recently, of experimental measurements - is extrapolated from shorter wavelengths. Lab measurements of dust analogues, however, show that FIR opacities are usually higher than the values used in models and depend on temperature, which suggests…
The project Galactic Cold Cores has made Herschel observations of interstellar clouds where the Planck satellite survey has located cold and compact clumps. The sources range from starless clumps to protostellar cores. We examine 116 Herschel fields to estimate the submillimetre dust opacity and its variations. The submillimetre dust opacity was derived from Herschel data, and near-infrared observations of the reddening of background stars are converted into near-infrared optical depth. We studied the systematic errors affecting these parameters and used modelling to correct for the expected b…
In this study, we explore the impact of inhomogeneities in the spatial distribution of interstellar dust on spatial scales of $\le1$ au caused by ion shadowing forces on the optical properties of diffuse interstellar medium (ISM) as well as on the dust temperature. We show that recently proposed possibility that interstellar dust grains in the diffuse ISM are grouped in spherical cloudlets (clumps) may significantly affect the observed optical properties of the diffuse ISM in comparison to that calculated under the commonly accepted assumption on the uniform dust/gas mixture if the size of clu…
Effects of temperature-dependent optical properties on the determination of interstellar dust masses
National Chung Hsing University（国立中兴大学）；Tamkang University（淡江大学）；Institute of Astronomy and Astrophysics, Academia Sinica（中央研究院天文及天文物理研究所）；Institut de Ciències de l’Espai (ICE, CSIC)（太空科学研究所（CSIC））；ICREA（加泰罗尼亚高级研究学院）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, College Lane Campus, University of Hertfordshire（赫特福德大学天体物理学研究中心）；Space Science Institute（空间科学研究所）；Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México（墨西哥国立自治大学射电天文学与天体物理研究所）
The submillimeter opacity of dust in the diffuse Galactic interstellar medium (ISM) has been quantified using a pixel-by-pixel correlation of images of continuum emission with a proxy for column density. We used three BLAST bands at 250, 350, and 500 μm and one IRAS at 100 μm. The proxy is the near-infrared color excess, E(J-Ks), obtained from 2MASS. Based on observations of stars, we show how well this color excess is correlated with the total hydrogen column density for regions of moderate extinction. The ratio of emission to column density, the emissivity, is then known from the correlation…
We have studied the opacity of dust grains at submillimeter wavelengths by estimating the optical depth from imaging at 160, 250, 350, and 500 um from the Herschel Gould Belt Survey and comparing this to a column density obtained from the 2MASS-derived color excess E(J-Ks). Our main goal was to investigate the spatial variations of the opacity due to "big" grains over a variety of environmental conditions and thereby quantify how emission properties of the dust change with column (and volume) density. The central and southern areas of the Orion A molecular cloud examined here, with NH ranging …
Synchrotron self-absorption in active galactic nuclei (AGN) jets manifests itself as a time delay between flares observed at high and low radio frequencies. It is also responsible for the observing frequency dependent change in size and position of the apparent base of the jet, aka the core shift effect, detected with very long baseline interferometry (VLBI). We measure the time delays and the core shifts in 11 radio-loud AGN to estimate the speed of their jets without relying on multi-epoch VLBI kinematics analysis. The 15$-$8 GHz total flux density time lags are obtained using Gaussian proce…
In extragalactic jets, the apparent position of the bright/narrow end (the core) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. The effect must be taken into account in order to achieve unbiased results from multi-frequency VLBI data on AGN jets. Multi-frequency core shift measurements supplemented by other data enable estimating the absolute geometry and a number of fundamental physical properties of the jets and their environment. We have previously measured the shift between 13 and 3.6 cm in a sample of 29 AGNs to range between 0 and 1.4 ma…
Galactic neutral hydrogen (HI) within a few hundred parsecs of the Sun contains structure with an angular distribution that is similar to small-scale structure observed by the Wilkinson Microwave Anisotropy Probe (WMAP). A total of 108 associated pairs of associated HI and WMAP features have now been cataloged using HI data mapped in 2 km/s intervals and these pairs show a typical offset of 0.8 degrees. A large-scale statistical test for a direct association is carried out that casts little additional light on whether the these small offsets are merely coincidental or carry information. To pur…
Radio pulsars emit regular bursts of radio radiation that propagate through the interstellar medium (ISM), the tenuous gas and plasma between the stars. Previously known dispersive properties of the ISM cause low frequency pulses to be delayed in time with respect to high frequency ones. This effect can be explained by the presence of free electrons in the medium. The ISM also contains neutral hydrogen which has a well known resonance at 1420.4 MHz. Electro-magnetic theory predicts that at such a resonance, the induced dispersive effects will be drastically different from those of the free ele…
This paper presents a finding of the correlation between the width of a strong diffuse interstellar band at 6196A and the excitation temperature of C2 based on high resolution and high signal-to-noise ratio spectra. The excitation temperature was determined from absorption lines of the Phillips A-X and Mulliken D-X systems. The width and shape of the narrow 6196A DIB profile apparently depend on the C2 temperature, being broader for higher values.
Variations in the observed dust emission and extinction indicate a systematic evolution of grain properties in the transition from the diffuse interstellar medium (ISM) to denser molecular clouds. The differences in the dust spectral energy distribution (SED) observed from the diffuse ISM to denser regions, namely an increase in the spectral index at long wavelengths, an increase in the FIR opacity, and a decrease in temperature, are usually assumed to be the result of changes in dust properties. We investigate if evolutionary processes, such as coagulation and accretion, are able to change th…
(Abridged) Many of the observed CO line profiles exhibit broad linewidths that greatly exceed the thermal broadening expected within molecular clouds. These suprathermal CO linewidths are assumed to be originated from the presence of unresolved supersonic motions inside clouds. Typically overlooked in the literature, in this paper we aim to quantify the impact of the opacity broadening effects on the current interpretation of the CO suprathermal line profiles. Without any additional contributions to the gas velocity field, a large fraction of the apparently supersonic (${\cal M}\sim$2-3) linew…
The content of interstellar clouds, in particular the inventory of diffuse molecular gas, remains uncertain. We identified a sample of isolated clouds, approximately 100 solar masses in size, and used the dust content to estimate the total amount of gas. In Paper 1, the total inferred gas content was found significantly larger than that seen in 21-cm emission measurements of atomic hydrogen. In this paper we test the hypothesis that the apparent excess 'dark' gas is cold atomic hydrogen, which would be evident in absorption but not in emission due to line saturation. The results show there is …
We are motivated by the recent measurements of dust opacity indices beta around young stellar objects (YSOs), which suggest that efficient grain growth may have occurred earlier than the Class I stage. The present work makes use of abundant archival interferometric observations at submillimeter,millimeter, and centimeter wavelength bands to examine grain growth signatures in the dense inner regions (<1000 AU) of nine Class 0 YSOs. A systematic data analysis is performed to derive dust temperatures, optical depths, and dust opacity indices based on single-component modified black body fittings …
The intensity of the far-ultraviolet (FUV; 6-13.6 eV) interstellar radiation field (ISRF) in galaxies determines the thermal and chemical evolution of the neutral interstellar gas and is key for interpreting extragalactic observations and for theories of star-formation. We run a series of galactic disk models and derive the FUV ISRF intensity as a function of the dust-to-gas ratio, star-formation rate density, gas density, scale radius, and observer position. We develop an analytic formula for the median FUV ISRF flux. We identify two dimensionless parameters in the problem: (1) the dimensionl…
It is well known that interstellar spectral features correlate with color excess E(B$-$V). This suggests that measuring intensities of these features allows one to estimate reddening of stars. The aim of this paper is to check how tight intensities of interstellar diffuse bands (DIBs)are related to the amount of extinction, measured using E(B$-$V). We have measured equivalent widths of the strongest DIBs (centered at $λλ$ 5780.6, 5797.0, 6196.0, 6379.3, 6613.5, and 8620.7 A), as well as of CH (near 4300.3 A) and CH$^+$ (near 4232.5 A) in high resolution, high S/N ratio echelle spectra from sev…
We present a detailed study of the surface brightness profiles of dense filaments in IC 5146 using recent Herschel observations done with SPIRE. We describe the profile through an equilibrium solution of a self-gravitating isothermal cylinder pressure confined by its surrounding medium. In this first analysis we applied a simple modified black body function for the emissivity, neglecting any radiative transfer effects. Overall we found a good agreement of the observed surface brightness profiles with the model. The filaments indicate strong self-gravity with mass line densities M/l\gtrsim 0.5 …
We derive two-dimensional spatial power spectra of four distinct interstellar medium tracers, HI, $^{12}$CO($J$=1--0), $^{13}$CO($J$=1--0), and dust, in the Perseus molecular cloud, covering linear scales ranging from $\sim$0.1 pc to $\sim$90 pc. Among the four tracers, we find the steepest slopes of $-3.23\pm0.05$ and $-3.22\pm0.05$ for the uncorrected and opacity-corrected HI column density images. This result suggests that the HI in and around Perseus traces a non-gravitating, transonic medium on average, with a negligible effect from opacity. On the other hand, we measure the shallowest sl…
There remain many open questions relating to the depletion of elements into dust, e.g., exactly how are C and O incorporated into dust in dense clouds and, in particular, what drives the disappearance of oxygen in the denser interstellar medium? This work is, in part, an attempt to explain the apparently anomalous incorporation of O atoms into dust in dense clouds. We re-visit the question of the depletion of the elements incorporated into the carbonaceous component of interstellar dust, i.e., C, H, O, N and S, in the light of recent analyses of the organics in comets, meteorites and interplan…
The metallicity and gas density dependence of interstellar depletions, the dust-to-gas (D/G), and dust-to-metal (D/M) ratios have important implications for how accurately we can trace the chemical enrichment of the universe; either by using FIR dust emission as a tracer of the ISM; or by using spectroscopy of damped Lyman-alpha systems (DLAs) to measure chemical abundances over a wide range of redshifts. We collect and compare large samples of depletion measurements in the Milky Way (MW), LMC (Z=0.5 Zsun), and SMC (Z=0.2 Zsun). The relation between the depletions of different elements do not …
Mapping of near-infrared (NIR) scattered light is a recent method for the study of interstellar clouds, complementing other, more commonly used methods, like dust emission and extinction. Our goal is to study the usability of this method on larger scale, and compare the properties of a filament using NIR scattering and other methods. We also study the radiation field and differences in grain emissivity between diffuse and dense areas. We have used scattered J, H, and K band surface brightness WFCAM-observations to map filament TMC-1N in Taurus, covering an area of 1dx1d corresponding to ~(2.44…
Using the Planck far-infrared and Arecibo GALFA 21-cm line surveys, we identified a set of isolated interstellar clouds (approximately degree-sized on the sky and comprising 100 solar masses) and assessed the ratio of gas mass to dust mass. Significant variations of the gas-to-dust ratio are found both from cloud to cloud and within regions of individual clouds; within the clouds, the atomic gas per unit dust decreases by more than a factor of 3 compared to the standard gas-to-dust ratio. Three hypotheses are considered. First, the apparently low gas-to-dust ratio could be due to molecular gas…
Many things in current interstellar dust studies are taken as well understood givens by much of the community. For example, it is widely held that interstellar dust is made up of only three components, i.e., astronomical silicates, graphite and polycyclic aromatic hydrocarbons, and that our understanding of these is now complete and sufficient enough to interpret astronomical observations of dust in galaxies. To zeroth order this is a reasonable approximation. However, while these three pillars of dust modelling have been useful in advancing our understanding over the last few decades, it is n…
We study infrared emission of 17 isolated, diffuse clouds with masses of order solar masses, to test the hypothesis that grain property variations cause the apparently low gas-to-dust ratios that have been measured in those clouds. Maps of the clouds were constructed from WISE data and directly compared to the maps of dust optical depth from Planck. The mid-infrared emission per unit dust optical depth has a significant trend toward lower values at higher optical depths. The trend can be quantitatively explained by extinction of starlight within the clouds. The relative amounts of PAH and very…
We observed the L1506 filament, which is located in the Taurus molecular complex, with the Herschel PACS and SPIRE instruments. Our aim is to prove the variation in grain properties along the entire length of the filament. In particular, we want to determine above which gas density this variation arises and what changes in the grain optical properties/size distribution are required. We use the 3D radiative transfer code CRT, coupled to the dust emission and extinction code DustEM, to model the emission and extinction of the dense filament. We test a range of optical properties and size distrib…
We report the detection of absorption lines by the reactive ions OH+, H2O+ and H3O+ along the line of sight to the submillimeter continuum source G10.6$-$0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+ at 971 GHz, H2O+ at 1115 and 607 GHz, and H3O+ at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6$-$0.4 as well as in the molecular gas directly associated with that source. The OH+ spectrum reaches saturat…
Understanding the effects of dust extinction is important to properly interpret observations. The optical total-to-selective extinction ratio, Rv = Av/E(B-V), is widely used to describe extinction variations in ultraviolet and optical bands. Since the Rv=3.1 extinction curve adequately represents the average extinction law of diffuse regions in the Milky Way, it is commonly used to correct observational measurements along sightlines toward diffuse regions in the interstellar medium. However, the Rv value may vary even along different diffuse interstellar medium sightlines. In this paper, we in…
Stardust Galaxies at z>9: A Dust-Origin Transition Behind the Excess of UV-Bright Galaxies
Aix Marseille Université（艾克斯-马赛大学）；Waseda University（早稻田大学）；Nagoya University（名古屋大学）；the Institute of Statistical Mathematics（统计数学研究所）；David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto（多伦多大学戴维·A·邓普尔天文与天体物理系）；National Optical-Infrared Astronomy Research Laboratory（国家光学红外天文研究实验室）；University of Hertfordshire（赫特福德大学）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）
We present the analysis of supernova remnants (SNRs) in the Large Magellanic Cloud (LMC) and their influence on the environment at far-infrared (FIR) and submillimeter wavelengths. We use new observations obtained with the {\it Herschel} Space Observatory and archival data obtained with the {\it Spitzer} Space Telescope, to make the first FIR atlas of these objects. The SNRs are not clearly discernible at FIR wavelengths, however their influence becomes apparent in maps of dust mass and dust temperature, which we constructed by fitting a modified black-body to the observed spectral energy dist…
Starlight that becomes linearly polarized by magnetically aligned dust grains provides a viable diagnostic of the interstellar magnetic field (ISMF). A survey is underway to map the local ISMF using data collected at eight observatories in both hemispheres. Two approaches are used to obtain the magnetic structure: statistically evaluating magnetic field directions traced by multiple polarization position angles, and least-squares fits that provide the dipole component of the magnetic field. We find that the magnetic field in the circumheliospheric interstellar medium (CHM), which drives winds …
We offer a new, more inclusive, picture of the local interstellar medium, where it is composed of a single, monolithic cloud that surrounds the Sun in all directions. Our study of velocities based on Mg II and Fe II ultraviolet absorption lines indicates that the cloud has an average motion consistent with the velocity vector of gas impacting the heliosphere and does not behave like a rigid body: gas within the cloud is being differentially decelerated in the direction of motion, and the cloud is expanding in directions perpendicular to this flow, much like the squashing of a balloon. The oute…
We present a comprehensive 5-43 GHz VLBA study of the blazar 3C 273 initiated after an onset of a strong $γ$-ray flare in this source. We have analyzed the kinematics of new-born components, light curves, and position of the apparent core to pinpoint the location of the $γ$-ray emission. Estimated location of the $γ$-ray emission zone is close to the jet apex, 2 pc to 7 pc upstream from the observed 7 mm core. This is supported by ejection of a new component. The apparent core position was found to be inversely proportional to frequency. The brightness temperature in the 7 mm core reached valu…
Astrophysical bow shocks are a common result of the interaction between two supersonic plasma flows, such as winds or jets from stars or active galaxies, or streams due to the relative motion between a star and the interstellar medium. For cylindrically symmetric bow shocks, we develop a general theory for the effects of inclination angle on the apparent shape. We propose a new two-dimensional classification scheme for bow shapes, which is based on dimensionless geometric ratios that can be estimated from observational images. The two ratios are related to the flatness of the bow's apex, which…
We investigate radiative feedback from a 34 M$_\odot$ star in a $10^4$ M$_\odot$ turbulent cloud using three-dimensional radiation-hydrodynamics (RHD) models. We use Monte Carlo radiative transfer to accurately compute photoionization equilibrium and radiation pressure, with multiple atomic species and silicate dust grains. We include the diffuse radiation field, dust absorption/re-emission, and scattering. The cloud is efficiently dispersed, with 75 per cent of the mass leaving the (32.3 pc)$^3$ grid within 4.3 Myr (1.1 $t_{ff}$). This compares to all mass exiting within 1.6 Myr (0.74 $t_{ff}…
The motivation to study experimentally CO ice under mimicked interstellar conditions is supported by the large CO gas abundances and ubiquitous presence of CO in icy grain mantles. Upon irradiation in its pure ice form, this highly stable species presents a limited ion and photon-induced chemistry, and an efficient non-thermal desorption. Using infrared spectroscopy, single laser interference, and quadrupole mass spectrometry during CO ice deposition, the CO ice density was estimated as a function of deposition temperature. Only minor variations in the density were found. The proposed methodol…
An absorption feature is occasionally reported around 11 microns in astronomical spectra, including those of forming stars. Candidate carriers include water ice, polycyclic aromatic hydrocarbons (PAHs), silicon carbide, crystalline silicates or even carbonates. All are known constituents of cosmic dust in one or more types of environments, though not necessarily together. In this paper we present new ground-based 8-13 micron spectra of one evolved star, several embedded young stellar objects (YSOs) and a background source lying behind a large column of the interstellar medium (ISM) toward the …
We have explored the capabilities of dust extinction and $γ$ rays to probe the properties of the interstellar medium in the nearby anti-centre region. We have jointly modelled the $γ$-ray intensity and the stellar reddening, E(B-V) as a combination of H$_{\rm I}$-bright, CO-bright, and ionised gas components. The complementary information from dust reddening and $γ$ rays is used to reveal the dark gas not seen, or poorly traced, by H$_{\rm I}$, free-free, and $^{12}$CO emissions. We compare the total gas column densities, $N_{\rm{H}}$, derived from the $γ$ rays and stellar reddening with those…
Bow shocks and related density enhancements produced by the winds of massive stars moving through the interstellar medium provide important information regarding the motions of the stars, the properties of their stellar winds, and the characteristics of the local medium. Since bow shocks are aspherical structures, light scattering within them produces a net polarization signal even if the region is spatially unresolved. Scattering opacity arising from free electrons and dust leads to a distribution of polarized intensity across the bow shock structure. That polarization encodes information abo…
