Population Synthesis Models for Late BuildUp of the Red Sequence.pdf

Draft version February 5, 2008 A Preprint typeset using L T X style emulateapj v. 6/22/04 E POPULATION SYNTHESIS MODELS FOR LATE BUILD-UP OF THE RED SEQUENCE 1 1,2 1,3 1 Justin J. Harker , Ricardo P. Schiavon , Benjamin J. Weiner , S. M. Faber Draft version February 5, 2008 ABSTRACT We present population synthesis models designed to represent the star formation histories of L∗ red sequence galaxies (RSGs). Earlier work has shown that single-burst stellar populations (SSPs) are unable to match Balmer line strengths simultaneously at high and low redshift. We therefore consider alternative star formation histories in which RSGs contain intermediate-aged stars even at late epochs. The models are compared to Balmer HδF absorption strengths, U −B color data, and 6 0 the number density of red sequence galaxies from z = 1 to z = 0. We find that quenched models, 0 models of constant star formation histories truncated at regularly-spaced intervals, average to an RSG 2 population that matches the data well, showing slow evolution in color and Balmer line strength and a rise in number density by a factor of a few after z = 1. The data are best fit by a turn-on of quenching l u at redshifts z = 1.5 − 2. J Subject headings: galaxies: evolution, galaxies: formation, galaxies: stellar content