Rongmon Bordoloi

Current and future weak lensing surveys will rely on photometrically estimated redshifts of very large numbers of galaxies. We investigate several different aspects of the demanding photo-z performance that will be required for future experiments, such as the proposed ESA Euclid mission. We show that the proposed all-sky near-infrared photometry from Euclid, in combination with anticipated ground-based photometry (e.g. PanStarrs-2 or DES) can yield the required high precision in individual photo-z of sigma(z) < 0.05(1+z) . We introduce simple a priori rejection scheme based on the photometry alone, which can be tuned to recognise objects with wildly discrepant photo-z and sufficiently reduce the outlier fraction with only modest loss of otherwise usable objects. We introduce a simple adaptive scheme based on the statistical properties of the photo-z likelihood functions which helps to precisely characterize the lensing tomographic bins . We investigate the effect of an imprecise correction for Galactic extinction and the effects of contamination by fainter over-lapping objects in photo-z determination. We further examine the effect of large scale structure in the spectroscopic survey field whilst estimating the lensing N(z) from direct sampling of spectroscopic redshifts.

The bias in the mean redshift of the tomographic bins estimated from the sum of the likelihood functions for several surveys simulated. For survey-B (PanStaars2 or DES combined with Euclid near infrared photometry) we meet the Euclid survey requirements given in the shaded region. For more information see Bordoloi et al 2009.