Galaxy populations in intermediate-redshift clusters

Abstract

Clusters of galaxies are ideal laboratories to study the evolution of galaxies. High redshift clusters especially provide the opportunity to look back in time and analyse the galaxy populations at early epochs and compare them with those in clusters like Coma and Virgo in our vicinity. Since the seminal work of Butcher ~z Oemler (1978a) we know that significant evolution has taken place over the past few giga-years, since rich clusters at redshifts of about 0.5 contain significantly more blue (i.e. star-forming) galaxies than e.g. the Coma cluster (Butcher and Oemler, 1984). Analysing galaxy populations in clusters over a wide range in redshift will thus be a powerful tool in our study of galaxy evolution in general. Although the Butcher-Oemler effect was discovered by photometry in two filters only, its verification required time consuming slit spectroscopy. A few years ago we began a project at MPIA in Heidelberg to develop tools to analyse the galaxy populations in high redshift clusters more reliably and in a more efficient way than previously possible. The primary goals have been to