Do dark matter halos explain lensing peaks?

We have investigated a recently proposed halo-based model, Camelus, for predicting weak-lensing peak counts, and compared its results over a collection of 162 cosmologies with those from N-body simulations. While counts from both models agree for peaks with S/N > 1 (where S/N is the ratio of the peak height to the r.m.s. shape noise), we find ≈ 50% fewer counts for peaks near S/N = 0 and significantly higher counts in the negative S/N tail. Adding shape noise reduces the differences to within 20% for all cosmologies. We also found larger covariances that are more sensitive to cosmological parameters. As a result, credibility regions in the {Ωm, σ8} are ≈ 30% larger. Even though the credible contours are commensurate, each model draws its predictive power from different types of peaks. Low peaks, especially those with 2 < S/N < 3, convey important cosmological information in N-body data, as shown in [1, 2], but Camelus constrains cosmology almost exclusively from high significance peaks (S/N > 3). Our results confirm the importance of using a cosmology-dependent covariance with at least a 14% improvement in parameter constraints. We identified the covariance estimation as the main driver behind differences in inference, and suggest possible ways to make Camelus even more useful as a highly accurate peak count emulator.