The redshift evolution of early-type galaxies in COSMOS: Do massive early-type galaxies form by dry mergers?

C. Scarlata, C. M. Carollo, S. J. Lilly, R. Feldmann, P. Kampczyk, A. Renzini, A. Cimatti, C. Halliday, E. Daddi, M. T. Sargent, A. Koekemoer, N. Scoville, J. P. Kneib, A. Leauthaud, R. Massey, J. Rhodes, L. Tasca, P. Capak, H. J. McCracken, B. MobasherY. Taniguchi, D. Thompson, M. Ajiki, H. Aussel, T. Murayama, D. B. Sanders, S. Sasaki, Y. Shioya, M. Takahashi

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129 Scopus citations


We study the evolution since z ∼ 1 of the rest-frame B luminosity function of ETGs in ∼0.7 deg 2 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.

Original languageEnglish (US)
Pages (from-to)494-510
Number of pages17
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - 2007


  • Galaxies: elliptical and lenticular, cD
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: structure


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