New insights on the accuracy of photometric redshift measurements

We use the deepest and most complete redshift catalog currently available ( the Hubble Deep Field (HDF) North supplemented by new HDF South redshift da ta) to minimize residuals between photometric and spectroscopic redshift es timates. The good agreement at z(spec) < 1.5 shows that model libraries pro vide a good description of the galaxy population. At z(spec) <greater than or equal to> 2.0, the systematic shift between photometric and spectroscopi c redshifts decreases when the modeling of the absorption by the interstell ar and intergalactic media is refined. As a result, in the entire redshift range z is an element of [0, 6], residuals between photometric and spectros copic redshifts are roughly halved. For objects fainter than the spectrosco pic limit, the main source of uncertainty in photometric redshifts is relat ed to photometric errors, and can be assessed with Monte Carlo simulations.