Baryon impact on weak lensing peaks and power spectrum: Low-bias statistics and self-calibration in future surveys

Peaks in two-dimensional weak lensing (WL) maps contain significant cosmological information, complementary to the WL power spectrum. This has recently been demonstrated using N-body simulations which neglect baryonic effects. Here we employ ray-tracing N-body simulations to source galaxies at redshift z(s) = 2 in which we manually steepen the density profile of each dark matter halo, mimicking the cooling and concentration of baryons into dark matter potential wells. We find, in agreement with previous works, that this causes a significant increase in the amplitude of the WL power spectrum on small scales (spherical harmonic index l greater than or similar to 1,000). We then study the impact of the halo concentration increase on the peak counts, and find the following. (i) Low peaks (with convergence 0.02 less than or similar to kappa(peak) less than or similar to 0.08) remain nearly unaffected. These peaks are created by a constellation of several halos with low masses (similar to 10(12)-10(13)M(circle dot)) and large angular offsets from the peak center (greater than or similar to 0.5R(vir)); as a result, they are insensitive to the central halo density profiles. These peaks contain most of the cosmological information, and thus provide an unusually sensitive and unbiased probe. (ii) The number of high peaks (with convergence kappa(peak) greater than or similar to 0.08) is increased. However, when the baryon effects are neglected in cosmological parameter estimation, then the high peaks lead to a modest bias, comparable to that from the power spectrum on relatively large scales (l < 2000), and much smaller than the bias from the power spectrum on smaller scales (l > 2000). (iii) In the three-dimensional parameter space (sigma(8), Omega(m), w), the biases from the high peaks and the power spectra are in different directions. This suggests the possibility of self-calibration: the combination of peak counts and power spectrum can simultaneously constrain baryonic physics and cosmological parameters. DOI: 10.1103/PhysRevD.87.023511