Distribution of extinction and star formation in NGC 1569

Abstract

We investigate the spatial distribution of the intrinsic extinction in the starburst dwarf galaxy NGC 1569 using an extinction map of the whole galaxy derived from the mbox H α/ mbox H β emission line ratio. We differentiate the extinction in the H ii regions from the extinction of the diffuse gas. The intrinsic extinction shows considerable variations over the plane of the galaxy, from negligible extinction up to A_V = 0.8 mag. The extinction map shows small scale clumpy structures possibly due to a clumpy dust distribution. We also identify a shell structure in this map, for which we establish a causal relation with the expanding gas structure produced by the stellar winds coming from the Super Star Clusters (SSC) in the center of the galaxy. The comparison of the spatial profiles of the extinction, dust and gaseous emissions crossing the border of the shell shows a layered structure; the peak of this mbox H α distribution lies closest to the SSC A, followed outwards by the peak of the extinction and at a still larger distance by the bulk of the atomic gas. We suggest that the extinction shell has been produced by the SSC and that it can be explained by the accumulation of dust at the border of this ionized gas structure.