paper

The Butcher-Oemler Effect at Low Redshift: Spectroscopy of Five Nearby Clusters of Galaxies

arXiv:astro-ph/9611001 · doi:10.1086/118271

Abstract

We present multi-fiber spectroscopy and broadband imaging of early-type galaxies in five nearby rich clusters of galaxies. The main purpose was to look for ``abnormal'' spectrum galaxies (i.e., post-starburst galaxies which have strong Balmer absorption lines and emission line galaxies) in nearby clusters that are similar to those found by Caldwell et al. (1993) in the Coma cluster. Our primary conclusion is that 15% of the early-type galaxies in these nearby rich clusters have signs of ongoing or recent star formation. Thus activity similar to that seen in distant clusters is still ongoing, at a reduced level, in present-epoch rich clusters. The frequency of such galaxies appears to be enhanced significantly over that seen in field galaxies. Most of the new post-starburst galaxies are disk galaxies; three E galaxies in one cluster and one in another cluster have current star formation. We also find evidence in the spatial and kinematic structure of several of the clusters that subclusters have recently passed through the main clusters and are now emerging out the other side. If, as we suspect, the subclusters passed through the main clusters more than 1 Gyr ago, then the post-starburst timescales of 1 Gyr imply that the star formation bursts are only triggered during (or after) the subcluster passage through the center of the main cluster.

To appear in the Astronomical Journal. 68 pages including 24 pages of figures. To include the gif images of Fig 12 in postscript form, use xv to change gif to ps with names as given in the tex file, and uncomment the appropriate lines in the figure caption area of tex file

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