CaltechAUTHORS
Published September 2007 | Version Published
Journal Article Open

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

Creators

  • 1. ROR icon ETH Zurich
  • 2. ROR icon Space Telescope Science Institute
  • 3. ROR icon California Institute of Technology
  • 4. ROR icon Laboratoire d'Astrophysique de Marseille
  • 5. ROR icon Jet Propulsion Lab
  • 6. ROR icon Institut d'Astrophysique de Paris
  • 7. ROR icon University of Padua
  • 8. ROR icon University of Hawaii at Hilo
  • 9. ROR icon University of Arizona
  • 10. ROR icon Tohoku University
  • 11. ROR icon University of Hawaii at Manoa
  • 12. ROR icon CEA Saclay
  • 13. ROR icon Ehime University

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 early-type galaxies and (2) an excess of a factor of about 3, at a similar redshift, of irregular galaxies.

Additional Information

© 2007 American Astronomical Society. Print publication: Issue 1 (2007 September); received 2006 April 25, accepted for publication 2006 November 5. The HST COSMOS Treasury program was supported through NASA grant HST-GO-09822.We gratefully acknowledge the contributions of the entire COSMOS collaboration. More information on the COSMOS survey is available at http://cosmos.astro .caltech.edu.We thank the NASA IPAC/IRSA staff for providing online archive and server capabilities for the COSMOS data sets. C. S. acknowledges support from the Swiss National Science Foundation. Facilities: HST (ACS)

Attached Files

Published - SCAapjss07.pdf

Files

SCAapjss07.pdf

Files (4.6 MB)

Name Size
md5:136c2916f8a667b14b5489085f0680fb
4.6 MB Preview Download

Additional details

Identifiers

Eprint ID
17712
Resolver ID
CaltechAUTHORS:20100309-143207444

Funding

NASA
HST-GO-09822
Swiss National Science Foundation (SNSF)

Dates

Created
2010-03-10
Created from EPrint's datestamp field
Updated
2021-11-08
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
COSMOS , Infrared Processing and Analysis Center (IPAC)