A deeper view of Extremely Red Galaxies: the redshift distribution in the GOODS/CDFS ISAAC field

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  • 6 January 2004
Abstract
We have analysed 5-epoch GOODS HST-ACS B, V, I and z datasets (V1.0 release), in conjunction with existing VLT-ISAAC imaging in the J, H and Ks bands, to derive estimated redshifts for the sample of 198 Extremely Red Galaxies (ERGs) with Ks3.92 selected by Roche et al. (2003) from 50.4 sq. arcmin of the GOODS/CDFS field. We find that, at this depth, the ERG population spans the redshift range 0.5L* population at redshifts zphot>2. We have investigated the existence of high-redshift Lyman break galaxies massive enough to be included in this ERG sample. Out of an initial list of 12 potential very high redshift candidates, we have identified 5 ERGs which have a very high probability of lying at zphot>4. 4/5 of these objects are very massive (>10^11 Msun) and could account for a comoving density of progenitors of local L>L* galaxies of ~ (2.9 +/- 1.5)x 10^(-5) Mpc^(-3). Finally, we discuss the advantages of multi-colour to single-colour selection techniques in obtaining reliable lists of very high-redshift candidate sources, and present revised lower redshift estimates for four sources previously claimed as potential z>5 dropouts in recent studies.

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