ABSTRACT. We study the evolution since z ~ 1 of the rest-frame B luminosity function of ETGs in ~0.7 deg² in the COSMOS field. In order to identify all progenitors of local ETGs we construct the sample of high-z galaxies using two complementary criteria: (1) a morphological selection based on the Zurich Estimator of Structural Types and (2) a photometric selection based on the galaxy properties in the (U - V)-M_V color-magnitude diagram. We furthermore constrain both samples so as to ensure that the selected progenitors of ETGs are compatible with evolving into systems that obey the μ_B-r_hl Kormendy relation. Assuming the luminosity evolution derived from studies of the fundamental plane for high-z ETGs, our analysis shows no evidence for a decrease in the number density of the most massive ETGs out to z ~ 0.7: both the morphologically and the photometrically selected subsamples show no evolution in the number density of bright (~L > 2.5L*) ETGs. Allowing for different star formation histories, and cosmic variance, we estimate a maximum decrease in the number density of massive galaxies at that redshift of ~30%. We observe, however, in both the photometric and morphological samples, a deficit of up to about 2-3 of fainter ETGs over the same cosmic period. Our results argue against a significant contribution of recent dissipationless "dry'' mergers to the formation of the most massive ETGs. We suggest that the mass growth in low-luminosity ETGs can be explained with a conversion from z ~ 0.7 to z = 0 of blue, irregular, and disk galaxies into low- and intermediate-mass "red'' ETGs, possibly also through gas-rich mergers.

Subject headings: galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: formation; galaxies: structure

^* Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Print publication: Issue 1 (2007 September)
Received 2006 June 16, accepted for publication 2007 January 26