Photo-z Performance for Precision Cosmology II : Empirical Verification
  The success of future large scale weak lensing surveys will critically depend
on the accurate estimation of photometric redshifts of very large samples of
galaxies. This in turn depends on both the quality of the photometric data and
the photo-z estimators. In a previous study, (Bordoloi et al. 2010) we focussed
primarily on the impact of photometric quality on photo-z estimates and on the
development of novel techniques to construct the N(z) of tomographic bins at
the high level of precision required for precision cosmology, as well as the
correction of issues such as imprecise corrections for Galactic reddening. We
used the same set of templates to generate the simulated photometry as were
then used in the photo-z code, thereby removing any effects of "template
error". In this work we now include the effects of "template error" by
generating simulated photometric data set from actual COSMOS photometry. We use
the trick of simulating redder photometry of galaxies at higher redshifts by
using a bluer set of passbands on low z galaxies with known redshifts. We find
that "template error" is a rather small factor in photo-z performance, at the
photometric precision and filter complement expected for all-sky surveys. With
only a small sub-set of training galaxies with spectroscopic redshifts, it is
in principle possible to construct tomographic redshift bins whose mean
redshift is known, from photo-z alone, to the required accuracy of 0.002(1+z).
