Photometric Redshifts and Selection of High-Redshift Galaxies in the NTT and Hubble Deep Fields

We present and compare in this paper new photometric redshift catalogs of the galaxies in three public fields: the NTT Deep Field, the HDF-N, and the HDF-S. In the case of the NTT Deep Field, we present here a new photometric catalog, obtained by combining the existing BVrI and JKs with new deep U observations acquired with NTT-SUSI2, and which includes also the contiguous field centered on the zem = 4.7 quasar BR 1202-07. Photometric redshifts have been obtained for the whole sample (NTTDF + HDF-N + HDF-S), by adopting a χ2 minimization technique on a spectral library drawn from the Bruzual and Charlot synthesis models, with the addition of dust and intergalactic absorption. The accuracy, determined from 125 galaxies with known spectroscopic redshifts, is σz ~ 0.08 (0.3) in the redshift intervals z = 0–1.5 (1.5–3.5). The global redshift distribution of I-selected galaxies shows a distinct peak at intermediate redshifts, z 0.6 at IAB ≤ 26 and z 0.8 at IAB ≤ 27.5 followed by a tail extending to z 6. Systematic differences exist among the fields, most notably the HDF-S which contains a much smaller number of galaxies at z 0.9 and at z ≥ 4.5 than the HDF-N. We also present for the first time the redshift distribution of the total IR-selected sample to faint limits (Ks ≤ 21 and J ≤ 22). It is found that the number density of galaxies at 1.25 5 candidates in the HDF filter set and that the four brightest candidates at z > 5 in the HDF-S are indeed most likely M stars.