On the Origins of Starburst and Poststarburst Galaxies in Nearby Clusters

HST WFPC2 images in B (F450W) and I (F814W) have been obtained for threestarburst (SB) and two post-starburst (PSB) galaxies in the Coma cluster, andfor three such galaxies in the cluster DC2048-52. V (F555W) and I images for anadditional PSB galaxy in Coma have been extracted from the archive. Seven ofthese galaxies were previously classified as E/S0 on the basis of ground-basedimages, one as Sa, and the other as an irregular. The HST images reveal these SB/PSB galaxies to be heterogeneous inmorphology. Nevertheless a common theme is that many of them, especially the SBgalaxies, tend to have centralized spiral structure that appears simply as abright ``bulge''on ground-based images. In addition, while some PSB galaxiesexhibit distinct spiral structure, on the whole they have smoother morphologiesthan the SB galaxies. The morphologies and luminosity profiles are generallyconsistent with substantial starbursts in the form of centralized spiralstructure (the SB galaxies) which fade into smoother morphologies (the PSBgalaxies), with lingering spectroscopic evidence for past central starbursts.An important point is that the PSB galaxies retain disks, i.e, they have notevolved into spheroidal systems.Comment: 32 pages, 10 figures including 3 jpg images. To appear in the January 1999 Astronomical Journa