Evolutionary Synthesis Models for Galaxy Transformation in Clusters.pdf

Evolutionary Synthesis Models for Galaxy Transformation in Clusters Jens Bicker, U. Fritze-v. Alvensleben, K. J. Fricke Universit¨ats-Sternwarte G¨ottingen 30.09.2002 2 Abstract. The galaxy population in rich local galaxy clusters shows a ratio of one 0 quarter elliptical galaxies, two quarters S0 galaxies, and one quarter spiral galaxies. 0 Observations of clusters at redshift 0.5 show a perspicuously different ratio, the 2 dominant galaxy type are spiral galaxies with a fraction of two quarters while the t number of S0 galaxies decreases to a fraction of one quarter (Dressler et al. 1997). c This shows an evolution of the galaxy population in clusters since redshift 0.5 and O it has been suspected that galaxy transformation processes during the infall into a cluster are responsible for this change. These could be merging, starburst or ram- 1 pressure stripping. We use our evolutionary synthesis models to describe various 3 possible effects of those interactions on the star formation of spiral galaxies infalling into clusters. We study the effects of starbursts of various strengths as well as of the 1 v truncation of star formation at various epochs on the color and luminosity evolution 6 of model galaxies of various spectral types. As a first application we present the 7 comparison of our models with observed properties of the local S0 galaxy population 6