The Evolution of the Field and Cluster Morphology‐Density Relation for Mass‐Selected Samples of Galaxies

The Sloan Digital Sky Survey (SDSS) and photometric/spectroscopic surveys in the GOODS-South field (the Chandra Deep Field-South, CDF-S) are used to construct volume-limited, stellar-mass-selected samples of galaxies at redshifts 0 2.5. The fraction of E + S0 galaxies is 43% ± 3% at z ∼ 0.03 and 48% ± 7% at z ∼ 0.8; i.e., it has not changed significantly since z ∼ 0.8. When combined with recent results for cluster galaxies in the same redshift range, we find that the morphology-density relation for galaxies more massive than 0.5M* has remained constant since at least z ∼ 0.8. This implies that galaxies evolve in mass, morphology, and density such that the morphology-density relation does not change. In particular, the decline of star formation activity and the accompanying increase in the stellar mass density of red galaxies since z ∼ 1 must happen without large changes in the early-type galaxy fraction in a given environment.