Accounting for Baryons in Cosmological Constraints from Cosmic Shear
  One of the most pernicious theoretical systematics facing upcoming
gravitational lensing surveys is the uncertainty introduced by the effects of
baryons on the power spectrum of the convergence field. One method that has
been proposed to account for these effects is to allow several additional
parameters (that characterize dark matter halos) to vary and to fit lensing
data to these halo parameters concurrently with the standard set of
cosmological parameters. We test this method. In particular, we use this
technique to model convergence power spectrum predictions from a set of
cosmological simulations. We estimate biases in dark energy equation of state
parameters that would be incurred if one were to fit the spectra predicted by
the simulations either with no model for baryons, or with the proposed method.
We show that neglecting baryonic effect leads to biases in dark energy
parameters that are several times the statistical errors for a survey like the
Dark Energy Survey. The proposed method to correct for baryonic effects renders
the residual biases in dark energy equation of state parameters smaller than
the statistical errors. These results suggest that this mitigation method may
be applied to analyze convergence spectra from a survey like the Dark Energy
Survey. For significantly larger surveys, such as will be carried out by the
Large Synoptic Survey Telescope, the biases introduced by baryonic effects are
much more significant. We show that this mitigation technique significantly
reduces the biases for such larger surveys, but that a more effective
mitigation strategy will need to be developed in order ensure that the residual
biases in these surveys fall below the statistical errors.
