How Future Space-Based Weak Lensing Surveys Might Obtain Photometric
  Redshifts Independently
  We study how the addition of on-board optical photometric bands to future
space-based weak lensing instruments could affect the photometric redshift
estimation of galaxies, and hence improve estimations of the dark energy
parameters through weak lensing. Basing our study on the current proposed
Euclid configuration and using a mock catalog of galaxy observations, various
on-board options are tested and compared with the use of ground-based
observations from the Large Synoptic Survey Telescope (LSST) and Pan-STARRS.
Comparisons are made through the use of the dark energy Figure of Merit, which
provides a quantifiable measure of the change in the quality of the scientific
results that can be obtained in each scenario. Effects of systematic offsets
between LSST and Euclid photometric calibration are also studied. We find that
adding two (U and G) or even one (U) on-board optical band-passes to the
space-based infrared instrument greatly improves its photometric redshift
performance, bringing it close to the level that would be achieved by combining
observations from both space-based and ground-based surveys while freeing the
space mission from reliance on external datasets.
