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The age spread of quiescent galaxies with the NEWFIRM Medium-Band Survey: identification of the oldest galaxies out to z ~ 2

Whitaker, Katherine E.; van Dokkum, Pieter G.; Brammer, Gabriel; Kriek, Mariska; Franx, Marijn; Labbé, Ivo; Marchesini, Danilo; Quadri, Ryan F.; Bezanson, Rachel; Illingworth, Garth D.; Lee, Kyoung-Soo; Muzzin, Adam; Rudnick, Gregory and Wake, David A. (2010). The age spread of quiescent galaxies with the NEWFIRM Medium-Band Survey: identification of the oldest galaxies out to z ~ 2. Astrophysical Journal, 719(2) pp. 1715–1732.

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With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey, we study the stellar populations of the oldest and most massive galaxies (>1011 M) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected U−V colors out to z = 2.2, with accurate photometric redshifts, σz/(1 + z) ~ 2%, and rest-frame colors, σU−V ~ 0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame U−V colors of quiescent galaxies with redshift. This scatter in color arises from the spread in ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies toward higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000 Å and Balmer breaks, respectively. Some of the quiescent galaxies may be up to four times older than the average age and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed U−V color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies toward higher redshift, red mergers at z ≲ 1, and a frosting of relatively young stars from star formation at later times.

Item Type: Journal Item
Copyright Holders: 2010. The American Astronomical Society
ISSN: 1538-4357
Keywords: cosmology; galaxies; evolution; formation
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 38419
Depositing User: Astrid Peterkin
Date Deposited: 24 Sep 2013 09:41
Last Modified: 08 Dec 2018 13:21
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