Proceedings of the International Astronomical Union

Table of Contents - 2006 - Volume 2, Symposium S235 (Galaxy Evolution Across the Hubble Time)  

Contributed Papers

Massive and Evolved Galaxies at z ≥ 5

T. Wiklinda1, B. Mobashera1, M. Dickinsona2, H. Fergusona3, M. Giavaliscoa3, N. Grogina4 and N. Panagiaa3

a1 ESA/STScI, Baltimore, MD 21218, USA email: wiklind@stsci.edu

a2 NOAO, Tucson, AZ 85726, USA

a3 STScI, Baltimore, MD 21218, USA

a4 Johns Hopkins University, Baltimore, MD 21218, USA

Abstract

We search for massive and evolved galaxies at z ≥ 5 in the Great Observatories Origins Deep Survey (GOODS) southern field. Combining HST ACS, VLT ISAAC and Spitzer IRAC broad–band photometric data, we develop a color selection technique to identify candidates for being evolved galaxies at high redshifts. The color selection is primarily based on locating the Balmer–break using the K- and 3.6 μm bands. Stellar population synthesis models are fitted to the SEDs of these galaxies to identify the final sample. We find 11 candidates with photometric redshifts in the range 4.9 < z < 5.6, dominated by an old stellar population, with ages 0.2-1.0 Gyr, and stellar masses in the range (0.7 − 5) × 1011 Mxs2299. Most of the candidates have modest amounts of internal dust extinction. The majority of the stars in these galaxies were formed at z>9 and the current star formation activity is a few percent of the inferred initial star formation rate.

Keywords

  • galaxies: evolution;
  • galaxies: formation;
  • galaxies: high redshift
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