Early-type Galaxies at z ~ 1.3. II. Masses and Ages of Early-type Galaxies in Different Environments and Their Dependence on Stellar Population Model Assumptions
We have derived masses and ages for 79 early-type galaxies (ETGs) in different environments at z ~ 1.3 in the Lynx supercluster and in the GOODS/CDF-S field using multi-wavelength (0.6-4.5 μm; KPNO, Palomar, Keck, Hubble Space Telescope, Spitzer) data sets. At this redshift the contribution of the thermally pulsing asymptotic giant branch (TP-AGB) phase is important for ETGs, and the mass and age estimates depend on the choice of the stellar population model used in the spectral energy distribution fits. We describe in detail the differences among model predictions for a large range of galaxy ages, showing the dependence of these differences on age. Current models still yield large uncertainties. While recent models from Maraston and Charlot & Bruzual offer better modeling of the TP-AGB phase with respect to less recent Bruzual & Charlot models, their predictions do not often match. The modeling of this TP-AGB phase has a significant impact on the derived parameters for galaxies observed at high redshift. Some of our results do not depend on the choice of the model: for all models, the most massive galaxies are the oldest ones, independent of the environment. When using the Maraston and Charlot & Bruzual models, the mass distribution is similar in the clusters and in the groups, whereas in our field sample there is a deficit of massive (M ≳ 10^(11) M_☉) ETGs. According to those last models, ETGs belonging to the cluster environment host on average older stars with respect to group and field populations. This difference is less significant than the age difference in galaxies of different masses.
Additional Information© 2011 American Astronomical Society. Received 2010 November 8; accepted 2011 February 18; published 2011 April 7. 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 grant for 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 recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We 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 Association of Universities for Research in Astronomy, lnc., 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 (United Kingdom), the National Research Council (Canada), CONlCYT (Chile), the Australian Research Council (Australia), Ministrio da Cincia e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnologa e lnnovacin Productiva (Argentina),Gemini Science Program ID: GN-2006A-Q-78.We thank the anonymous referee for constructive comments. We thank Raphael Gobat and Veronica Strazzullo for useful discussions. Facilities: HST (ACS), Spitzer (IRAC), KPNO:2.1m (FLAMINGOS), Hale (COSMIC), Keck:I (LRIS)
Published - Raichoor2011p13677Astrophys_J.pdf