The Evolution of Star Formation in Early-type Galaxies

Abstract

How the star formation activity in early-type galaxies (ETGs) evolves over cosmic time provides observational constraints on the picture of the formation and evolution of ETGs. Using HST/ACS (Hubble Space Telescope/Advanced Camera for Surveys) imaging data from the GEMS (Galaxy Evolution from Morphology and SEDs) survey and multi-band data in the CDFS (Chandra Deep Field South), a complete sample of 456 ETGs within 0.2≤z≤1 is selected based on morphology, color and stellar mass. With stacking technique, the UV and IR average luminosities are derived from GALEX (Galaxy Evolution Explorer) and Spitzer observations and the average star formation rates are estimated. Our results show that the star formation intensities of ETGs are low SFR < 3 M_⊙ yr-1 and decline with decreasing redshift. The total stellar mass contributed by star formation since z=1 is less than 15%. Stellar population modeling confirms that the bulk of stars in ETGs were formed at early time (z>2).