Diffuse Dust Component Research Articles

Dust extinction map of the Galactic plane based on the VVV survey data

ABSTRACT Dust extinction is one of the most reliable tracers of the gas distribution in the Milky Way. The near-infrared (NIR) Vista Variables in the Vía Láctea (VVV) survey enables extinction mapping based on stellar photometry over a large area in the Galactic plane. We devise a novel extinction mapping approach, XPNICER, by bringing together VVV photometric catalogues, stellar parameter data from StarHorse catalogues, and previously published X percentile and PNICER extinction mapping techniques. We apply the approach to the VVV survey area, resulting in an extinction map that covers the Galactic disc between 295° ≲ l ≲ 350° and −2° ≲ b ≲ 2°, and the Galactic bulge between −10° ≲ b ≲ 5°. The map has 30 arcsec spatial resolution and it traces extinctions typically up to AV ∼ 10–20 mag and maximally up to AV ∼ 30 mag. We compare our map to previous dust-based maps, concluding that it provides a high-fidelity extinction-based map, especially in its ability to recover both the diffuse dust component of the Galaxy and moderately extincted giant molecular cloud regions. The map is especially useful as independent, extinction-based data on the Galactic dust distribution and applicable for a wide range of studies from individual molecular clouds to the studies of the Galactic stellar populations.

High-resolution synthetic UV–submm images for simulated Milky Way-type galaxies from the Auriga project

ABSTRACT We present redshift-zero synthetic observational data considering dust attenuation and dust emission for the 30 galaxies of the Auriga project, calculated with the skirt radiative transfer code. The post-processing procedure includes components for star-forming regions, stellar sources, and diffuse dust taking into account stochastic heating of dust grains. This allows us to obtain realistic high-resolution broad-band images and fluxes from ultraviolet (UV) to submillimetre (submm) wavelengths. For the diffuse dust component, we consider two mechanisms for assigning dust to gas cells in the simulation. In one case, only the densest or the coldest gas cells are allowed to have dust, while in the other case this condition is relaxed to allow a larger number of dust-containing cells. The latter approach yields galaxies with a larger radial dust extent and an enhanced dust presence in the interspiral regions. At a global scale, we compare Auriga galaxies with observations by deriving dust scaling relations using spectral energy distribution fitting. At a resolved scale, we make a multiwavelength morphological comparison with nine well-resolved spiral galaxies from the DustPedia observational data base. We find that for both dust assignment methods, although the Auriga galaxies show a good overall agreement with observational dust properties, they exhibit a slightly higher specific dust mass. The multiwavelength morphological analysis reveals a good agreement between the Auriga and the observed galaxies in the optical wavelengths. In the mid- and far-infrared wavelengths, Auriga galaxies appear smaller and more centrally concentrated in comparison to their observed counterparts. We publicly release the multi-observer images and fluxes in 50 commonly used broad-band filters.

NGC 4370: a case study for testing our ability to infer dust distribution and mass in nearby galaxies

A fraction of the early-type galaxy population hosts a prominent dust lane. Methods to quantify the dust content of these systems based on optical imaging data usually yield dust masses which are an order of magnitude lower than dust masses derived from the observed FIR emission. High-quality optical data from the Next Generation Virgo cluster Survey (NGVS) and FIR/submm observations from the Herschel Virgo Cluster Survey (HeViCS) allow us to revisit previous methods to determine the dust content in galaxies and explore new ones. We aim to derive the dust mass in NGC 4370 from both optical and FIR data, and investigate the need to invoke a putative diffuse dust component. We create color and attenuation maps, which are converted to approximate dust mass maps based on simple dust geometries. Dust masses are also derived from SED fits to FIR/submm observations. Finally, inverse radiative transfer fitting is performed to investigate more complex dust geometries. The empirical methods applied to the optical data yield lower limits of 3.4e5 solar masses, an order of magnitude below the total dust masses derived from SED fitting. In contrast, radiative transfer models yield dust masses which are slightly lower, but fully consistent with the FIR-derived mass. Dust is more likely to be distributed in a ring around the centre of NGC 4370 as opposed to an exponential disc or a simple foreground screen. Moreover, using inverse radiative transfer fitting, we are able to constrain most of the parameters describing these geometries. The resulting dust masses are high enough to account for the dust observed at FIR/submm wavelengths, so that no diffuse dust component needs to be invoked. We furthermore caution for the interpretation of dust masses and optical depths based on optical data alone, using overly simplistic star-dust geometries and the neglect of scattering effects. [ABRIDGED]

Dust spectral energy distributions of nearby galaxies: an insight from theHerschelReference Survey

We gather infrared (IR) photometric data from 8 to 500 microns (Spitzer, WISE, IRAS and Herschel) for all of the HRS galaxies. Draine & Li (2007) models are fit to the data from which the stellar contribution has been carefully removed. We find that our photometric coverage is sufficient to constrain all of the models parameters and that a strong constraint on the 20-60 microns range is mandatory to estimate the relative contribution of the photo-dissociation regions to the IR SED. The SED models tend to systematically under-estimate the observed 500 microns flux densities, especially for low mass systems. We provide the output parameters for all of the galaxies: the minimum intensity of the interstellar radiation field (ISRF), the fraction of PAH, the relative contribution of PDR and evolved stellar population to the dust heating, the $M_{dust}$ and the $L_{IR}$. For a subsample of gas-rich galaxies, we analyze the relations between these parameters and the integrated properties of galaxies, such as $M_*$, SFR, metallicity, H$\alpha$ and H-band surface brightness, and the FUV attenuation. A good correlation between the fraction of PAH and the metallicity is found implying a weakening of the PAH emission in galaxies with low metallicities. The intensity of the IRSF and the H-band and H$\alpha$ surface brightnesses are correlated, suggesting that the diffuse dust component is heated by both the young stars in star forming regions and the diffuse evolved population. We use these results to provide a new set of IR templates calibrated with Herschel observations on nearby galaxies and a mean SED template to provide the z=0 reference for cosmological studies. For the same purpose, we put our sample on the SFR-$M_*$ diagram. The templates are compared to the most popular IR SED libraries, enlightening a large discrepancy between all of them in the 20-100 microns range.

ACCESS - IV. The quenching of star formation in a cluster population of dusty S0s

We present an analysis of the mid-infrared (MIR) colours of 165 70um-detected galaxies in the Shapley supercluster core (SSC) at z=0.048 using panoramic Spitzer/MIPS 24 and 70um imaging. While the bulk of galaxies show f70/f24 colours typical of local star-forming galaxies, we identify a significant sub-population of 23 70micron-excess galaxies, whose MIR colours (f70/f24>25) are much redder and cannot be reproduced by any of the standard model infrared SEDs. These galaxies are found to be strongly concentrated towards the cores of the five clusters that make up the SSC, and also appear rare among local field galaxies, confirming them as a cluster-specific phenomenon. Their optical spectra and lack of significant UV emission imply little or no ongoing star formation, while fits to their panchromatic SEDs require the far-IR emission to come mostly from a diffuse dust component heated by the general interstellar radiation field rather than ongoing star formation. Most of these 70micron-excess galaxies are identified as ~L* S0s with smooth profiles. We find that almost every cluster galaxy in the process of star-formation quenching is already either an S0 or Sa, while we find no passive galaxies of class Sb or later. Hence the formation of passive early-type galaxies in cluster cores must involve the prior morphological transformation of late-type spirals into Sa/S0s, perhaps via pre-processing or the impact of cluster tidal fields, before a subsequent quenching of star formation once the lenticular encounters the dense environment of the cluster core. In the cases of many cluster S0s, this phase of star-formation quenching is characterised by an excess of 70um emission, indicating that the cold dust content is declining at a slower rate than star formation.

The far-infrared view of M87 as seen by the Herschel Space Observatory

AbstractThe origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We observed M87 with PACS and SPIRE as part of the Herschel Virgo Cluster Survey (HeViCS). We compare the new Herschel data with a synchrotron model based on infrared, submm and radio data to investigate the origin of the far-infrared emission. We find that both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87.

TheHerschelVirgo Cluster Survey

The origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We present Herschel PACS and SPIRE observations of M87, taken as part of the science demonstration phase observations of the Herschel Virgo Cluster Survey. We compare these data with a synchrotron model based on mid-infrared, far-infrared, submm and radio data from the literature to investigate the origin of the far-infrared emission. Both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87, which is not unexpected in the harsh X-ray environment of this radio galaxy sitting at the core of the Virgo Cluster.

Is the Galactic submillimeter dust emissivity underestimated?

We present detailed modeling of the spectral energy distribution (SED) of the spiral galaxies NGC 891, NGC 4013 and NGC 5907 in the far-infrared (FIR) and sub-millimeter (submm) wavelengths. The model takes into account the emission of the diffuse dust component, which is heated by the UV and optical radiation field produced by the stars, as well as the emission produced locally in star forming HII complexes. Radiative transfer simulations in the optical bands are used to constrain the stellar and dust geometrical parameters and the dust mass. We find that the submm emission predicted by our model cannot account for the observed fluxes at these wavelengths. Two scenarios that could account for the “missing” submm flux are examined. In the first scenario dust additional to that derived from the optical wavelengths is embedded in the galaxy in the form of a thin disk. This additional dust disk, which is not detectable in the optical and which is associated with the young stellar population, gives rise to additional submm emission, and makes the total flux match the observed values. The other scenario examines the possibility that the average emissivity at submm wavelengths of the dust grains found both in a diffuse component and in denser environments (e.g. molecular gas clouds) is higher than the values widely used in Galactic environments. This enhanced emissivity reproduces the observed FIR and submm fluxes with the dust mass equal to that derived from the optical observations. In the second scenario, we treat the submm emissivity as a free parameter and calculate its nominal value by fitting our model to the observed SED. We find a dust emissivity which is ~ times the often-used values for our Galaxy. Both scenarios can equally well reproduce the observed 850 μ m surface brightness for all three galaxies. However, we argue that the scenario of having more dust embedded in a second disk is not supported by the near infrared observations. At 2.16 μ m, the model images with a second dust disk reveal a prominent dust lane which is not present in the observations. Thus, the enhanced emissivity at submm wavelengths is a real possibility and the Galactic submillimeter dust emissivity may be underestimated.

Energy Sources of the Far‐Infrared Emission of M33

We present observations of the spiral galaxy M33 with Spitzer at 24, 70, and 160 μm. The excellent resolution and mapping capabilities of Spitzer combined with the proximity of M33 result in observations that enable a detailed study of the distribution of star formation (SF) and dust in the galaxy. We compare the morphology of M33 at far-infrared wavelengths with other standard SF indicators such as Hα and radio continuum using a Fourier filtering technique to separate the diffuse emission components from compact sources. We find that the infrared emission at 24 and 70 μm follows closely the structure of the ionized gas, indicating that it is heated largely by hot, ionizing stars. At 160 μm a diffuse cold dust component matches only approximately the structure of the old red stellar population or the distribution of blue light. It is, however, very similar to the structure of the diffuse nonthermal radio emission.

Kinematics of elliptical galaxies with a diffuse dust component – III. A Monte Carlo approach to include the effects of scattering

This paper is the third one in a series, intended to investigate how the observed kinematics of elliptical galaxies are affected by dust attenuation. In Papers I and II, we investigated the effects of dust absorption; here we extend our modelling in order to include the effects of scattering. We describe how kinematical information can be combined with the radiative transfer equation, and present a Monte Carlo code that can handle kinematical information in an elegant way. Compared to the case where only absorption is taken into account, we find that dust attenuation considerably affects the observed kinematics when scattering is included. For the central lines of sight, dust can either decrease or increase the central observed velocity dispersion. The most important effect of dust attenuation, however, is found at large projected radii. The kinematics at these lines of sight are strongly affected by photons scattered into these lines of sight, that were emitted by high-velocity stars in the central regions of the galaxy. These photons bias the line-of-sight velocity distributions (LOSVDs) towards high line-of-sight velocities, and significantly increase the observed velocity dispersion and LOSVD shape parameters. These effects are similar to the expected kinematical signature of a dark matter halo, such that dust attenuation may form an alternative explanation for the usual stellar kinematical evidence for dark matter haloes around elliptical galaxies. We apply our results to discuss several other topics in galactic dynamics, where we feel dust attenuation should be taken into account. In particular, we argue that the kinematics observed at various wavelengths can help to constrain the spatial distribution of dust in elliptical galaxies.

Kinematics of elliptical galaxies with a diffuse dust component - II. Dust effects on kinematic modelling

Observations have demonstrated the presence of substantial amounts of interstellar dust in elliptical galaxies, most of which is believed to be distributed diffusely over the galaxy. Absorption by dust grains has a major impact on the transfer of stellar radiation, and affects the projection of each physical (and kinematic) quantity. In a previous paper, we have investigated the effects of a diffusely distributed dust component on the observed kinematics of spherical galaxies. In this paper we investigate the effect of not taking dust into account in dynamical modelling procedures. We use a set of semi-analytical dusty galaxy models to create synthetic line-of-sight velocity distribution (LOSVD) data sets, which we then model as if no dust were present. We find some considerable differences between the best-fitting models and the input models, and we find that these differences are dependent on the orbital structure of the input galaxy. For radial and isotropic models on the one hand, we find that the dynamical mass of the models decreases nearly linearly with optical depth, with an amount of 5 per cent per optical depth unit, whereas their orbital structure is hardly affected. For tangential models on the other hand, the dynamical mass decrease is smaller, but their orbital structure is affected: their distribution functions appear less tangentially anisotropic. For all models the mass-to-light ratio will be underestimated, by a factor of around 20 per cent per optical depth unit. We discuss these results in the light of the limited effects of dust extinction on the LOSVDs, as obtained in Paper I, and conclude that the determination of the dynamical mass and the kinematic structure of galaxies is not only determined by the observed kinematic quantities, but is also critically dependent on the potential and hence the observed light profile. We argue that dust, even in rather modest amounts, should therefore be taken into account in kinematic modelling procedures.

Kinematics of elliptical galaxies with a diffuse dust component

Observations show that early-type galaxies contain a considerable amount of interstellar dust, most of which is believed to exist as a diffusely distributed component. We construct a four-parameter elliptical galaxy model in order to investigate the effects of such a smooth absorbing component on the projection of kinematic quantities, such as the line profiles and their moments. We investigate the dependence of these effects on the optical depth and on the dust geometry. Our calculations show that both the amplitude and the morphology of these quantities can be significantly affected. The effects of dust should therefore be taken into consideration when interpreting photometric and kinematic properties, and in correlations that utilize these quantities.

Obscuration by Diffuse Cosmic Dust

AbstractIf the background universe is observed through a significant amount of diffusely distributed foreground dust, then studies at optical wavelengths may be severely biased. Previous studies investigating the effects of foreground dust on background sources assumed dust to be ‘compactly’ distributed, i.e. on scales comparable to the visible extent of normal galaxies. We show, however, that diffuse dust is more effective at obscuring background sources. Galaxy clusters are a likely location for ‘large-scale’ diffusely distributed dust, and its effect on the counts of background sources is explored. We also explore the implications of a hypothesised diffuse intergalactic dust component uniformly distributed to high redshift with comoving mass density equal to that associated with local galaxies. In this case, we predict a deficit in background sources about three times greater than that found in previous studies.