Morphologies and star formation in z ∼ 0.5 group galaxies

Abstract

As groups today contain ∼60% of the galaxy population [1], and are the first step in the hierarchical growth tree which dominates structure formation, these environments must have a critical influence on the evolution of star formation in the Universe as a whole. Indeed their dynamics make them the ideal environments to foster galaxy-galaxy interactions and mergers, leading to a dramatic transformation of galaxy properties. To study the evolution of galaxies in groups requires highly complete, targetted, deep spectroscopic surveys. At intermediate redshift, the only such is our sample of 26 groups at 0.3 < z < 0.55, selected from the CNOC2 redshift survey [2], with additional targetted spectroscopy using the Magellan 6.5m and VLT telescopes providing a complete kinematic description to a depth of ∼M * +3 at z = 0.4. [3]. Our full multiwavelength dataset will include HST-ACS, GALEX UV, Chandra, XMM and Spitzer imaging, with the power to ultimately reveal the importance of the group environment in controlling the evolutionary fate of a galaxy. In this contribution, we present some of the more recent and illuminating analysis, revealing evolution in the group environment and the dependence of star-formation and galaxy morphologies upon environment and stellar mass. Finally we discuss the important role Spitzer will play in revealing the processes actively transforming galaxies in the group environment. © 2007 Springer.