Directly Detecting the Evolution of Early-Type Galaxies

Abstract

We describe observations focused on understanding the epochs and timescales of the formation and evolution of early-type galaxies, particularly those in clusters. We show that while early-type cluster galaxies are on average older and closer to coeval than their counterparts in the field, significant age spreads (a factor of two in massive ellipticals, more in low-mass galaxies, especially S0’s) still exist in these objects. We then show that it is now possible to detect the evolution of early-type galaxies directly by comparing deep absorption-line spectroscopy of intermediate-redshift cluster galaxies with local cluster galaxies. We find that the stellar populations of early-type cluster galaxies do indeed evolve, at a rate that appears to be consistent with the cosmological lookback time.