Cosmos morphological classification with the Zurich estimator of structural types (ZEST) and the evolution since z = 1 of the luminosity function of early, disk, and irregular galaxies

C. Scarlata, C. M. Carollo, S. Lilly, M. T. Sargent, R. Feldmann, P. Kampczyk, C. Porciani, A. Koekemoer, N. Scoville, J. P. Kneib, A. Leauthaud, R. Massey, J. Rhodes, L. Tasca, P. Capak, C. Maier, H. J. McCracken, B. Mobasher, A. Renzini, Y. TaniguchiD. Thompson, K. Sheth, M. Ajiki, H. Aussel, T. Murayama, D. B. Sanders, S. Sasaki, Y. Shioya, M. Takahashi

Research output: Contribution to journalArticlepeer-review

209 Citations (Scopus)

Abstract

Motivated by the desire to reliably and automatically classify structure of thousands of COSMOS galaxies, we present ZEST, the Zurich Estimator of Structural Types. To classify galaxy structure, ZEST uses (1) five nonparametric diagnostics: asymmetry, concentration, Gini coefficient, second-order moment of the brightest 20% of galaxy pixels, and ellipticity; and (2) the exponent n of single-Sérsic fits to the two-dimensional surface brightness distributions. To fully exploit the wealth of information while reducing the redundancy present in these diagnostics, ZEST performs a principal component (PC) analysis. We use a sample of ∼56,000 I AB ≤ 24 COSMOS galaxies to show that the first three PCs fully describe the key aspects of the galaxy structure, i.e., to calibrate a three-dimensional classification grid of axes PC 1, PC 2, and PC 3. We demonstrate the robustness of the ZEST grid on the z = 0 sample of Frei et al. The ZEST classification breaks most of the degeneracy between different galaxy populations that affects morphological classifications based on only some of the diagnostics included in ZEST. As a first application, we present the evolution since z ∼ 1 of the luminosity functions (LFs) of COSMOS galaxies of early, disk, and irregular galaxies and, for disk galaxies, of different bulge-to-disk ratios. Overall, we find that the LF up to a redshift z = 1 is consistent with a pure luminosity evolution (of about 0.95 mag at z ∼ 0.7). We highlight, however, two trends that are in general agreement with a downsizing scenario for galaxy formation, i.e., (1) a deficit of a factor of about 2 at z ∼ 0.7 of M B > -20.5 structurally classified earlytype galaxies and (2) an excess of a factor of about 3, at a similar redshift, of irregular galaxies.

Original languageEnglish
Pages (from-to)406-433
Number of pages28
JournalAstrophysical Journal, Supplement Series
Volume172
Issue number1
DOIs
Publication statusPublished - 2007

Keywords

  • Cosmology: observations
  • Dark matter
  • Galaxies: evolution
  • Galaxies: formation
  • Large-scale structure of universe
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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