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Title

The Gemini Deep Deep Survey VIII : when did early-type galaxies form?

Author(s)

Abraham, Roberto G.;  Nair, Preethi;  McCarthy, Patrick J.;  Glazebrook, Karl;  Mentuch, Erin;  Yan, Haojing;  Savaglio, Sandra;  Crampton, David;  Murowinski, Richard;  Juneau, Stephanie;  Le Borgne, Damien;  Carlberg, Ray G.;  Jørgensen, Inger;  Roth, Kathy;  Chen, Hsiao Wen;  Marzke, Ronald O.

Abstract

We have used the Hubble Space Telescope's Advanced Camera for Surveys (Ford et al. 2003) to measure the cumulative mass density in morphologically selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight lines and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultradeep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purpose-written morphological analysis code, which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z similar to 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strongmorphology-mass relationship seen in the nearby universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range.

Publication type

Journal article

Source

Astrophysical Journal, Vol. 669, no. 1 (November 2007), p. 184-201

Publication year

2007

Keyword(s)

Digital sky survey;  Elliptic galaxies;  Field galaxies;  Galaxy evolution;  High-redshift galaxies;  HST;  Hubble Space Telescope;  Luminosity function;  Mass-metallicity relation;  Morphological classification;  Photometric redshifts;  Star formation history;  Stellar mass

Publisher

University of Chicago Press

ISSN

0004-637X

Publisher URL

http://dx.doi.org/10.1086/521138

Copyright

Copyright © 2007 The American Astronomical Society. All rights reserved. Reproduced in accordance with the copyright policy of the publisher.

Full text

Peer reviewed