The buildup of the Hubble sequence in the cosmos field

P. A. Oesch, C. M. Carollo, R. Feldmann, O. Hahn, S. J. Lilly, M. T. Sargent, C. Scarlata, M. C. Aller, H. Aussel, M. Bolzonella, T. Bschorr, K. Bundy, P. Capak, O. Ilbert, J. P. Kneib, A. M. Koekemoer, K. Kovač, A. Leauthaud, E. Le Floc'H, R. MasseyH. J. McCracken, L. Pozzetti, A. Renzini, J. Rhodes, M. Salvato, D. B. Sanders, N. Scoville, K. Sheth, Y. Taniguchi, D. Thompson

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Abstract

We use 8600 COSMOS galaxies at mass scales >5 × 1010 M to study how the morphological mix of massive ellipticals, bulge-dominated disks, intermediate-bulge disks, disk-dominated galaxies, and irregular systems evolves from z = 0.2 to z = 1. The morphological evolution depends strongly on mass. At M > 3 × 1011 M , no evolution is detected in the morphological mix: ellipticals dominate since z = 1, and the Hubble sequence has quantitatively settled down by this epoch. At the 1011 M mass scale, little evolution is detected, which can be entirely explained by major mergers. Most of the morphological evolution from z = 1 to z = 0.2 takes place at masses 5 × 1010-1011 M , where (1) the fraction of spirals substantially drops and the contribution of early types increases. This increase is mostly produced by the growth of bulge-dominated disks, which vary their contribution from ∼ 10% at z = 1 to >30% at z = 0.2 (for comparison, the elliptical fraction grows from ∼ 15% to 20%). Thus, at these masses, transformations from late to early types result in diskless elliptical morphologies with a statistical frequency of only 30%-40%. Otherwise, the processes which are responsible for the transformations either retain or produce a non-negligible disk component. (2) The disk-dominated galaxies, which contribute ∼ 15% to the intermediate-mass galaxy population at z = 1, virtually disappear by z = 0.2. The merger rate since z = 1 is too low to account for the disappearance of these massive disk-dominated systems, which most likely grow a bulge via secular evolution.

Original languageEnglish (US)
Pages (from-to)L47-L51
JournalAstrophysical Journal Letters
Volume714
Issue number1 PART 2
DOIs
StatePublished - 2010

Keywords

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

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