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Peaks in two-dimensional weak lensing (WL) maps contain significantcosmological information, complementary to the WL power spectrum. This hasrecently been demonstrated using N-body simulations which neglect baryoniceffects. Here we employ ray-tracing N-body simulations in which we manuallysteepen the density profile of each dark matter halo, mimicking the cooling andconcentration of baryons into dark matter potential wells. We find, inagreement with previous works, that this causes a significant increase in theamplitude of the WL power spectrum on small scales (spherical harmonic indexl>1,000). We then study the impact of the halo concentration increase on thepeak counts, and find the following. (i) Low peaks (with convergence 0.02 <kappa_peak < 0.08), remain nearly unaffected. These peaks are created by aconstellation of several halos with low masses (10^12-10^13 M_sun) and largeangular offsets from the peak center (> 0.5 R_vir); as a result, they areinsensitive to the central halo density profiles. These peaks contain most ofthe cosmological information, and thus provide an unusually sensitive andunbiased probe. (ii) The number of high peaks (with convergence kappa_peak >0.08) is increased. However, when the baryon effects are neglected incosmological 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>2,000). (iii) In the 3D parameter space (sigma_8, Omega_m, w), the biasesfrom the high peaks and the power spectra are in different directions. Thissuggests the possibility of "self-calibration": the combination of peak countsand power spectrum can simultaneously constrain baryonic physics andcosmological parameters.

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