Recent studies have shown that the number counts of convergence peaks N (κ) in weak lensing (WL) maps, expected from large forthcoming surveys, can be a useful probe of cosmology. We follow up on this finding, and use a suite of WL convergence maps, obtained from ray-tracing N-body simulations, to study (i) the physical origin of WL peaks with different heights, and (ii) whether the peaks contain information beyond the convergence power spectrum P . In agreement with earlier work, we find that high peaks (with amplitudes > ∼ 3.5σ, where σ is the r.m.s. of the convergence κ) are typically dominated by a single massive halo. In contrast, medium-height peaks (≈ 0.5 − 1.5σ) cannot be attributed to a single collapsed dark matter halo, and are instead created by the projection of multiple (typically, 4-8) halos along the line of sight, and by random galaxy shape noise. Nevertheless, these peaks dominate the sensitivity to the cosmological parameters w, σ8, and Ωm. We find that the peak height distribution and its dependence on cosmology differ significantly from predictions in a Gaussian random field. We directly compute the marginalized errors on w, σ8, and Ωm from the N (κ) + P combination, including redshift tomography with source galaxies at zs = 1 and zs = 2. We find that the N (κ) + P combination has approximately twice the cosmological sensitivity compared to P alone. These results demonstrate that N (κ) contains non-Gaussian information complementary to the power spectrum.PACS numbers: PACS codes: 95.36.+x, 98.65.Cw, 95.80.+p

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 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 > ∼ 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 < ∼ κ peak < ∼ 0.08), remain nearly unaffected. These peaks are created by a constellation of several halos with low masses (∼ 10 12 − 10 13 M ) and large angular offsets from the peak center ( > ∼ 0.5Rvir); 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 κ peak > ∼ 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 ( < 2000), and much smaller than the bias from the power spectrum on smaller scales ( > 2, 000). (iii) In the 3D parameter space (σ8, Ωm, 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.PACS numbers: PACS codes: 95.36.+x, 98.65.Cw, 95.80.+p

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