Clusters show consistent results from different studies: a tight color-magnitude relation for E-S0’s and very red colors that persist to quite high redshifts (z ∼ 1). These findings support the early bulge formation scenario, at least for some cluster galaxies (see van Dokkum & Franx 2001 giving a more complicated model). Studies of field populations, on the other hand, show no such consistency. Several studies favor scenarios with extensive and recent evolution by claiming that 30% to 50% of E-S0’s are blue at high redshifts (z < 1) or that the volume density of elliptical and red galaxies was 2 or 3 times lower in the past. Other studies find little evidence for such recent dramatic evolution.
Our deeper, more extensive, and less disk-contaminated observations challenge prior claims that 30% to 50% of field bulges or ellipticals are in a blue, star-forming phase at z < 1. We conclude that field bulges and ellipticals at z ~ 1, like luminous early- type cluster galaxies at the same redshift, are already dominated by metal-rich, old stellar populations that have been fading from a formation epoch earlier than z ~ 1.5.