Wide-Field Study of Distant Clusters of Galaxies with SPICA

¹ Department of Astronomy, School of Science, The University of Tokyo, Tokyo, Japan
² National Astronomical Observatory of Japan, Tokyo, Japan

Abstract

We propose an intensive, systematic study of distant clusters of galaxies at z ~ 0.5–5 and their surrounding infall regions, taking advantage of the significant wide fieldof-view of MIRACLE (6' × 6') and the high sensitivity at λ ≳ 20 μm of MIRACLE and SAFARI. Galaxy clusters and groups are mainly composed of red quiescent galaxies in the local Universe, but the star formation activity becomes much higher in distant clusters. Our coordinated AKARI/Subaru observations have revealed many dusty starburst galaxies in particular in intermediate-density environments such as groups at z ~ 1. Interestingly, this is also the same environment in which we see a sharp transition from blue galaxies to red ones. This suggests that dusty starbursts are strongly linked with the physical process that alters the properties of galaxies as they infall and assemble to higher density regions. We also expect that the site of galaxy formation with high star formation activity shifts to higher-density environments as we go back in time, probably due to spatial bias in galaxy formation. By observing many distant clusters at various redshifts between z ~ 0.5–5 with SPICA, and identifying dusty, star-forming galaxies across the wide area in and around the clusters/proto-clusters, we will trace back the star formation history of galaxies as a function of environment. We will thus be able to identify directly the epoch and the site of formation of present-day early-type galaxies.