TY - JOUR
T1 - The deep2 galaxy redshift survey
T2 - Mean ages and metallicies of red field galaxies at z ∼ 0.9 from stacked keck deimos spectr
AU - Schiavon, Ricardo P.
AU - Faber, S. M.
AU - Konidaris, Nicholas
AU - Graves, Genevieve
AU - Willmer, Christopher N.A.
AU - Weiner, Benjamin J.
AU - Coil, Alison L.
AU - Cooper, Michael C.
AU - Davis, Marc
AU - Harker, Justin
AU - Koo, David C.
AU - Newman, Jeffrey A.
AU - Yan, Renbin
PY - 2006/11/10
Y1 - 2006/11/10
N2 - As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 ≤ z ≤ 1. Comparison with models of stellar population synthesis shows that red galaxies at z ∼ 0.9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. These ages cannot be reconciled with a scenario in which all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that some star formation in the stacked populations continued to at least z ∼ 1.2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar population synthesis models, shows that the drop in the equivalent width of Hδ from z ∼ 0.9 to 0.1 is less than that predicted by passively evolving models. This admits two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z ∼ 0.9 to 0.1 is continually being added to by new galaxies with younger stars.
AB - As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 ≤ z ≤ 1. Comparison with models of stellar population synthesis shows that red galaxies at z ∼ 0.9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. These ages cannot be reconciled with a scenario in which all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that some star formation in the stacked populations continued to at least z ∼ 1.2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar population synthesis models, shows that the drop in the equivalent width of Hδ from z ∼ 0.9 to 0.1 is less than that predicted by passively evolving models. This admits two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z ∼ 0.9 to 0.1 is continually being added to by new galaxies with younger stars.
KW - Galaxies: distances and redshifts
KW - Galaxies: evolution
KW - Galaxies: stellar content
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U2 - 10.1086/509074
DO - 10.1086/509074
M3 - Article
AN - SCOPUS:33845769495
SN - 0004-637X
VL - 651
SP - L93-L96
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 II
ER -