Scarlata, C. and Carollo, C. M. and Lilly, S. and Sargent, M. T. and Feldmann, R. and Kampczyk, P. and Porciani, C. and Koekemoer, A. and Scoville, N. and Kneib, J.-P. and Leauthaud, A. and Massey, R. and Rhodes, J. and Tasca, L. and Capak, P. and Maier, C. and McCracken, H. J. and Mobasher, B. and Renzini, A. and Taniguchi, Y. and Thompson, D. and Sheth, K. and Ajiki, M. and Aussel, H. and Murayama, T. and Sanders, D. B. and Sasaki, S. and Shioya, Y. and Takahashi, M. (2007) 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. Astrophysical Journal Supplement Series, 172 (1). pp. 406-433. ISSN 0067-0049. http://resolver.caltech.edu/CaltechAUTHORS:20100309-143207444
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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)|
|Subject Keywords:||cosmology: observations; dark matter; galaxies: evolution; galaxies: formation; large-scale structure of universe; surveys|
|Official Citation:||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. Taniguchi, D. Thompson, K. Sheth, M. Ajiki, H. Aussel, T. Murayama, D. B. Sanders, S. Sasaki, Y. Shioya, and M. Takahashi 2007 ApJS 172 406-433 doi: 10.1086/516582|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||10 Mar 2010 17:12|
|Last Modified:||06 Jul 2015 21:18|
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