The dust distribution in edge-on galaxies

Abstract

Aims. I have analyzed a sample of seven nearby edge-on galaxies observed in the V and K � -bands, in order to infer the properties of the dust distribution. Methods. A radiative transfer model, including scattering, was used to decompose each image into a stellar disk, a bulge, and a dust disk. The parameters describing the distributions were obtained through standard χ 2 minimization techniques. Results. The dust disks fitted to the V-band images are consistent with previous work in the literature: the radial scalelength of dust is larger than for stars (hd/hs ∼ 1.5); the dust disk has a smaller vertical scalelength than the stellar (zd/zs ∼ 1/3); the dust disk is almost transparent when seen face-on (central, face-on, optical depth τ0 = 0.5−1.5). Equivalent fits can be produced using faster radiative transfer models that neglect scattering. In the K � -band, no trace is found of a second, massive, dust disk, which has been invoked to explain observations of dust emission in the submillimeter. I discuss the model degeneracies and the effect of complex structures on the fitted distributions. In particular, most bulges in the sample show a box/peanuts morphology with large residuals; two lower-inclination galaxies show a dust ring distribution, which could be the cause of the large, fitted, dust scalelengths.