The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies

Details The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies

2006-06-21

arxiv.org/abs/astro-ph/0606521v1

Astrophys.J.647:L21-L24,2006

Astronomy and Astrophysics

Astrophysics

4 pages, 4 figures, accepted for publication in ApJL

Scientific paper

10.1086/507297

We examine the origins of the bimodality observed in the global properties of galaxies around a stellar mass of 3x10^10 M_sun by comparing the environmental dependencies of star-formation for the giant and dwarf galaxy populations. The Sloan Digital Sky Survey DR4 spectroscopic dataset is used to produce a sample of galaxies in the vicinity of the supercluster centered on the cluster A2199 at z=0.03 that is ~90% complete to a magnitude limit of M*+3.3. From these we measure global trends with environment for both giant (M_r<-20 mag) and dwarf (-197 Gyr) or passive (EW[H_alpha]<4 A) falls gradually from ~80% in the cluster cores to ~40% in field regions beyond 3-4 R_virial, as found in previous studies. In contrast, we find that the dwarf galaxy population shows a sharp transition at ~1 R_virial, from being predominantly old/passive within the cluster, to outside where virtually all galaxies are forming stars and old/passive galaxies are only found as satellites to more massive galaxies. These results imply fundamental differences in the evolution of giant and dwarf galaxies: whereas the star-formation histories of giant galaxies are determined primarily by their merger history, star-formation in dwarf galaxies is much more resilient to the effects of major mergers. Instead dwarf galaxies become passive only once they become satellites within a more massive halo, by losing their halo gas reservoir to the host halo, or through other environment-related processes such as galaxy harassment and/or ram-pressure stripping.

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