The Canada-France Deep Fields III: Photometric Redshift Distribution to I(AB) ~ 24

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  • 1 October 2003
Abstract
We compute accurate redshift distributions to I(AB) = 24 and R(AB) = 24.5 using photometric redshifts estimated from 6-band photometry in the Canada-France Deep Fields-Photometric Redshift Survey (CFDF-PRS). Our photometric redshift algorithm is calibrated using hundreds of CFRS spectroscopic redshifts in the same fields. The dispersion in redshift is \sigma/(1+z) \la 0.04 to the CFRS depth of I(AB) = 22.5, rising to \sigma/(1+z) \la 0.06 at our nominal magnitude and redshift limits of I(AB) = 24 and z \le 1.3, respectively. We describe a new method to compute N(z) that incorporates the full redshift likelihood functions in a Bayesian iterative analysis and we demonstrate in extensive Monte Carlo simulations that it is superior to distributions calculated using simple maximum likelihood redshifts. A direct application of our results is in weak lensing cosmic shear studies, in which accurate source and lens plane redshift distributions are required to extract cosmological parameters from the convergence power spectrum. We therefore provide our measured I(AB) and R(AB) redshift distributions, the run of median redshifts, and parametrized fits of our results in various magnitude ranges. We account for both random and systematic errors in our analysis, and discuss the effects of cosmic variance on our survey and on measurements of N(z) in general.

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