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 (h d /h s ∼ 1.5); the dust disk has a smaller vertical scalelength than the stellar (z d /z s ∼ 1/3); the dust disk is almost transparent when seen face-on (central, face-on, optical depth τ 0 = 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.

FitSKIRT: genetic algorithms to automatically fit dusty galaxies with a Monte Carlo radiative transfer code

“…Parameters of the intrinsic distribution of stars and dust in NGC 4013 as obtained by FitSKIRT, by Bianchi (2007) and by Xilouris et al (1999). Notes.…”

“…Kylafis & Bahcall 1987;Xilouris et al 1997Xilouris et al , 1999Bianchi 2007Bianchi , 2008Baes et al 2010;Popescu et al 2011;MacLachlan et al 2011;Holwerda et al 2012). The system consists of a stellar disc, a stellar bulge and a dust disc.…”

“…Full details on the observations and data reduction can be found in Bianchi (2007). The image can be found in the top left panel of Fig.…”

“…In the last two columns of Table 2 we list the parameters found by Xilouris et al (1999) and Bianchi (2007), scaled to our Table 2. Parameters of the intrinsic distribution of stars and dust in NGC 4013 as obtained by FitSKIRT, by Bianchi (2007) and by Xilouris et al (1999).…”

“…In Sect. 4 we apply FitSKIRT to determine the intrinsic distribution of stars and dust in the galaxy NGC 4013, and we compare the resulting model to similar models obtained by Bianchi (2007) and Xilouris et al (1999). Section 5 sums up.…”