2007/05/23 by A. van der Wel, M. Franx, G. D. Illingworth +1
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #COSMIC cancer database #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Luminosity #Luminous infrared galaxy #Redshift #Sigma #Star formation #Stellar mass #astro-ph
paper · pdf · doi:10.1086/520055
published as Astrophys.J.666:863-869,2007 · Accepted for publication in ApJ, 8 pages, 4 figures, 1 table
arxiv created 2007/05/23 · openalex publication_date 2007/08/31 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We measure the obscured star formation in z ~ 1 early-type galaxies. This constrains the influence of star formation on their optical/near-IR colors, which, we found, are redder than predicted by the model by Bruzual & Charlot. From deep ACS imaging we construct a sample of 95 morphologically selected early-type galaxies in the HDF-N and CDF-S with spectroscopic redshifts in the range 0.85 < z < 1.15. We measure their 24 μm fluxes from the deep GOODS MIPS imaging and derive the IR luminosities and star formation rates (SFRs). The fraction of galaxies with >2 σ detections (~25 μJy) is 17 %. Of the 15 galaxies with significant detections, at least six have an AGN. Stacking the MIPS images of the galaxies without significant detections and adding the detected galaxies without AGNs we find an upper limit on the mean SFR of 5.2 ± 3.0 M ☉ yr -1 , and on the mean specific SFR of 4.6 ± 2.2 × 10 -11 yr -1 . Under the assumption that the average SFR will decline at the same rate as the cosmic average, the in situ growth in stellar mass of the early-type galaxy population is less than 14% ± 7% between z = 1 and the present. We show that the typically low IR luminosity and SFR imply that the effect of obscured star formation (or AGNs) on their rest-frame optical/near-IR SEDs is negligible for ~90% of the galaxies in our sample. Hence, their optical/near-IR colors are most likely dominated by evolved stellar populations. This implies that the colors predicted by the Bruzual & Charlot model for stellar populations with ages similar to those of z ~ 1 early-type galaxies (~1-3 Gyr) are most likely too blue, and that stellar masses of evolved, high-redshift galaxies can be overestimated by up to a factor of ~2.