Quantifying baryon effects on the matter power spectrum and the weak
  lensing shear correlation
  Feedback processes from baryons are expected to strongly affect weak-lensing
observables of current and future cosmological surveys. In this paper we
present a new parametrisation of halo profiles based on gas, stellar, and dark
matter density components. This parametrisation is used to modify outputs of
gravity-only $N$-body simulations (following the prescription of Schneider and
Teyssier [1]) in order to mimic baryonic effects on the matter density field.
The resulting baryonic correction model relies on a few well motivated physical
parameters and is able to reproduce the redshift zero clustering signal of
hydrodynamical simulations at two percent accuracy below $k\sim10$ h/Mpc. A
detailed study of the baryon suppression effects on the matter power spectrum
and the weak lensing shear correlation reveals that the signal is dominated by
two parameters describing the slope of the gas profile in haloes and the
maximum radius of gas ejection. We show that these parameters can be
constrained with the observed gas fraction of galaxy groups and clusters from
X-ray data. Based on these observations we predict a beyond percent effect on
the power spectrum above $k=0.2-1.0$ h/Mpc with a maximum suppression of 15-25
percent around $k\sim 10$ h/Mpc. As a result, the weak lensing angular shear
power spectrum is suppressed by 15-25 percent at scales beyond $\ell\sim
100-600$ and the shear correlations $\xi_{+}$ and $\xi_{-}$ are affected at the
10-25 percent level below 5 and 50 arc-minutes, respectively. The relatively
large uncertainties of these predictions are a result of the poorly known
hydrostatic mass bias of current X-ray observations as well as the generic
difficulty to observe the low density gas outside of haloes.
