Early-type Galaxies at z ~ 1.3. III. On the Dependence of Formation Epochs and Star Formation Histories on Stellar Mass and Environment
We study the environmental dependence of stellar population properties at z ~ 1.3. We derive galaxy properties (stellar masses, ages, and star formation histories) for samples of massive, red, passive early-type galaxies (ETGs) in two high-redshift clusters, RXJ0849+4452 and RXJ0848+4453 (with redshifts of z = 1.26 and 1.27, respectively), and compare them with those measured for the RDCS1252.9–2927 cluster at z = 1.24 and with those measured for a similarly mass-selected sample of field contemporaries drawn from the GOODS-South field. Robust estimates of the aforementioned parameters have been obtained by comparing a large grid of composite stellar population models with extensive 8- to 10-band photometric coverage, from the rest-frame far-ultraviolet to the infrared. We find no variations of the overall stellar population properties among the different samples of cluster ETGs. However, when comparing cluster versus field stellar population properties we find that, even if the ages are similar and depend only on galaxy mass, the ones in the field do employ longer timescales to assemble their final mass. We find that, approximately 1 Gyr after the onset of star formation, the majority (75%) of cluster galaxies have already assembled most (>80%) of their final mass, while, by the same time, fewer (35%) field ETGs have. Thus, we conclude that while galaxy mass regulates the timing of galaxy formation, the environment regulates the timescale of their star formation histories.
Additional Information© 2011 American Astronomical Society. Received 2010 November 22; accepted 2011 March 4; published 2011 April 21. A.R. is grateful to Gabriella de Lucia, Raphael Gobat, Roderik Overzier,Maurilio Pannella, Veronica Strazzullo, and Loredana Vetere for useful discussions. ACS was developed under NASA contract NAS 5-32865. This research has been supported by the NASA HST grant GO-10574.01-A, and Spitzer program 20694. The Space Telescope Science Institute is operated by AURA Inc., under NASA contract NAS5-26555. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. They are most fortunate to have the opportunity to conduct observations from this mountain. Some data were based on observations obtained at the Gemini Observatory, which is operated by the AURA, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministerio da Ciencia eTecnologia (Brazil), and Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina), Gemini Science Program ID: GN-2006A-Q-78. R.D. acknowledges the support provided by the BASAL Center for Astrophysics and Associated Technologies and by FONDECYT grant N. 1100540.
Published - Rettura2011p13852Astrophys_J.pdf