The influence of baryons on the clustering of matter and weak-lensing surveys

Future weak-lensing measurements of cosmic shear will reach such high accuracy that second-order effects in weak-lensing modeling, such as the influence of baryons on structure formation, become important. We use a controlled set of high-resolution cosmological simulations to quantify this effect by comparing pure N-body dark matter runs with corresponding hydrodynamic simulations, carried out both in nonradiative form and in dissipative form with cooling and star formation. In both hydrodynamic simulations, the clustering of the gas is suppressed while that of dark matter is boosted at scales k > 1 h Mpc(-1). Despite this counterbalance between dark matter and gas, the clustering of the total matter is suppressed by up to 1% at 1 h Mpc(-1) less than or similar to k less than or similar to 10 h Mpc(-1), while for k approximate to 20 h Mpc(-1) it is boosted, up to 2% in the nonradiative run and 10% in the run with star formation. The stellar mass formed in the latter is highly biased relative to the dark matter in the pure N-body simulation. Using our power spectrum measurements to predict the effect of baryons on the weak-lensing signal at scales corresponding to multipole moments 100 < l < 10,000, we find that baryons may change the lensing power spectrum by less than 0.5% at l < 1000, but by 1% to 10% at 1000 < l < 10,000. The size of the effect exceeds the predicted accuracy of future lensing power spectrum measurements and will likely be detected. Precise determinations of cosmological parameters with weak lensing, and studies of small-scale fluctuations and clustering, therefore rely on properly including baryonic physics.