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arXiv · astro-ph/0701746

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·Capak·H. J. McCracken·B. Mobasher·Y. Taniguchi·D. Thompson·M. Ajiki·H. Aussel·T. Murayama·D. B. Sanders·S. Sasaki·Y. Shioya·M. Takahashi
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Abstract

ABRIDGED: We study the evolution since z~1 of the rest-frame B luminosity function of the early-type galaxies (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: (i) A morphological selection based on the Zurich Estimator of Structural Types, and (ii) 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 which obey the mu_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 sub-samples 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 photometrical and morphological samples, a deficit of up to ~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.

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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, Capak, H. J. McCracken, B. Mobasher, Y. Taniguchi, D. Thompson, M. Ajiki, H. Aussel, T. Murayama, D. B. Sanders, S. Sasaki, Y. Shioya, M. Takahashi. 2007-02-07. The redshift evolution of early-type galaxies in COSMOS: Do massive early-type galaxies form by dry mergers?. https://doi.org/10.1086/517972

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