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Extragalactic astronomy relies on the accurate estimation of source photometry corrected for Milky Way dust extinction. This has motivated the creation of a number of Galactic dust maps. We investigate whether these maps are contaminated by extragalactic signals using the clustering-redshift technique, i.e., by measuring a set of angular cross-correlations with spectroscopic objects as a function of redshift. Our tomographic analysis reveals imprints of extragalactic large-scale structure patterns in nine out of 10 Galactic dust maps, including all infrared-based maps as well as stellar reddening maps. When such maps are used for extinction corrections, this extragalactic contamination introduces redshift- and scale-dependent biases in photometric estimates at the millimagnitude level. It can affect both object-based analyses, such as the estimation of the Hubble diagram with supernovae, as well as spatial statistics. The bias can be appreciable when measuring angular correlation functions with low amplitudes, such as lensing-induced correlations or angular correlations for sources distributed over a broad redshift range. As expected, we do not detect any extragalactic contamination for the dust map inferred from 21cm HI observations. Such a map provides an alternative to widely used infrared-based maps but relies on the assumption of a constant dust-to-gas ratio. We note that, using the WISE 12 micron map sensitive to polycyclic aromatic hydrocarbons (PAH), an indirect dust tracer, we detect the diffuse extragalactic PAH background up to $zsim2$. Finally, we provide a procedure to minimize the level of biased magnitude corrections in maps with extragalactic imprints.
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We present new three-dimensional (3D) interstellar dust reddening maps of the Galactic plane in three colours, E(G-Ks), E(Bp-Rp) and E(H-Ks). The maps have a spatial angular resolution of 6 arcmin and covers over 7000 deg$^2$ of the Galactic plane for Galactic longitude 0 deg $<$ $l$ $<$ 360 deg and latitude $|b|$ $<$ $10$ deg. The maps are constructed from robust parallax estimates from the Gaia Data Release 2 (Gaia DR2) combined with the high-quality optical photometry from the Gaia DR2 and the infrared photometry from the 2MASS and WISE surveys. We estimate the colour excesses, E(G-Ks), E(Bp-Rp) and E(H-Ks), of over 56 million stars with the machine learning algorithm Random Forest regression, using a training data set constructed from the large-scale spectroscopic surveys LAMOST, SEGUE and APOGEE. The results reveal the large-scale dust distribution in the Galactic disk, showing a number of features consistent with the earlier studies. The Galactic dust disk is clearly warped and show complex structures possibly spatially associated with the Sagittarius, Local and Perseus arms. We also provide the empirical extinction coefficients for the Gaia photometry that can be used to convert the colour excesses presented here to the line-of-sight extinction values in the Gaia photometric bands.
Gaia data are revolutionizing our knowledge of the evolutionary history of the Milky Way. 3D maps of the interstellar dust provide complementary information and are a tool for a wide range of uses. We aimed at building 3D maps of the dust in the Local arm and surrounding regions. To do so, Gaia DR2 photometric data were combined with 2MASS measurements to derive extinction towards stars that possess accurate photometry and relative uncertainties on DR2 parallaxes smaller than 20%. We applied to the extinctions a new hierarchical inversion algorithm adapted to large datasets and to a inhomogeneous target distribution. Each step associates regularized Bayesian
Winds driven by stellar feedback are an essential part of the galactic ecosystem and are the main mechanism through which low-mass galaxies regulate their star formation. These winds are generally observed to be multi-phase with detections of entrained neutral and molecular gas. They are also thought to enrich the circum-galactic medium around galaxies with metals and dust. This ejected dust encodes information about the integrated star formation and outflow history of the galaxy. It is therefore, important to understand how much dust is entrained and driven out of the disc by galactic winds. Here we demonstrate that stellar feedback is efficient in driving dust-enriched winds and eject enough material to account for the amount of extraplanar dust observed in nearby galaxies. The amount of dust in the wind depends on the sites from where they are launched, with dustier galaxies launching more dust enriched outflows. Moreover, the outflowing cold-dense gas is significantly more dust-enriched than the volume filling hot tenuous material, naturally reproducing the complex multiphase structure of the outflowing wind observed in nearby galaxies. These results provide an important new insight into the dynamics, structure, and composition of galactic winds and their role in determining the dust content of the extragalactic gas in galaxies.
We study the statistical properties of interstellar dust polarization at high Galactic latitude, using the Stokes parameter Planck maps at 353 GHz. Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a model of the polarized dust foreground for cosmic microwave background component-separation procedures. Focusing on the southern Galactic cap, we examine the statistical distributions of the polarization fraction ($p$) and angle ($psi$) to characterize the ordered and turbulent components of the Galactic magnetic field (GMF) in the solar neighbourhood. We relate patterns at large angular scales in polarization to the orientation of the mean (ordered) GMF towards Galactic coordinates $(l_0,b_0)=(70^circ pm 5^circ,24^circ pm 5^circ)$. The histogram of $p$ shows a wide dispersion up to 25 %. The histogram of $psi$ has a standard deviation of $12^circ$ about the regular pattern expected from the ordered GMF. We use these histograms to build a phenomenological model of the turbulent component of the GMF, assuming a uniform effective polarization fraction ($p_0$) of dust emission. To model the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of $N$ independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed $p$ and $psi$ distributions using: a $p_0$ value of (26 $pm$ 3)%; a ratio of 0.9 $pm$ 0.1 between the strengths of the turbulent and mean components of the GMF; and a small value of $N$. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS.
It has been suggested that the ratio of total-to-selective extinction RV in dust in the interstellar medium differs in the Galactic bulge from its value in the local neighborhood. We attempt to test this suggestion. The mid-infrared hydrogen lines in 16 Galactic bulge PNe measured by the Spitzer Space Telescope are used to determine the extinction corrected H{beta} flux. This is compared to the observed H{beta} flux to obtain the total extinction at H{beta}. The selective extinction is obtained from the observed Balmer decrement in these nebulae. The value of RV can then be found. The ratio of total-to-selective extinction in the Galactic bulge is consistent with the value RV =3.1, which is the same as has been found in the local neighborhood. We conclude that the suggestion that RV is different in the Galactic bulge is incorrect. The reasons for this are discussed.
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