Optimising cosmic shear surveys to measure modifications to gravity on
  cosmic scales
  We consider how upcoming photometric large scale structure surveys can be
optimized to measure the properties of dark energy and possible cosmic scale
modifications to General Relativity in light of realistic astrophysical and
instrumental systematic uncertainities. In particular we include flexible
descriptions of intrinsic alignments, galaxy bias and photometric redshift
uncertainties in a Fisher Matrix analysis of shear, position and position-shear
correlations, including complementary cosmological constraints from the CMB. We
study the impact of survey tradeoffs in depth versus breadth, and redshift
quality. We parameterise the results in terms of the Dark Energy Task Force
figure of merit, and deviations from General Relativity through an analagous
Modified Gravity figure of merit. We find that intrinsic alignments weaken the
dependence of figure of merit on area and that, for a fixed observing time, a
fiducial Stage IV survey plateaus above roughly 10,000deg2 for DE and peaks at
about 5,000deg2 as the relative importance of IAs at low redshift penalises
wide, shallow surveys. While reducing photometric redshift scatter improves
constraining power, the dependence is shallow. The variation in constraining
power is stronger once IAs are included and is slightly more pronounced for MG
constraints than for DE. The inclusion of intrinsic alignments and galaxy
position information reduces the required prior on photometric redshift
accuracy by an order of magnitude for both the fiducial Stage III and IV
surveys, equivalent to a factor of 100 reduction in the number of spectroscopic
galaxies required to calibrate the photometric sample.
