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

Abstract

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

Cosmological constraints from weak lensing peak statistics with Canada-France-Hawaii Telescope Stripe 82 Survey

“…This shows the capability to constrain the structural parameters of massive structures together with cosmological parameters from weak lensing peak statistics. With much improved data from future surveys, performing simultaneous constraints on the structural and cosmological parameters can potentially allow us to extract important astrophysical effects on the structural evolution of the mass distribution of halos (e.g., Yang et al 2013). Meanwhile, it can also avoid the possible bias on cosmological parameter constraints resulting from the pre-assumption about the halo structures in predicting the cosmological dependence of weak lensing peak abundances.…”

“…Besides cosmological parameter constraints, weak lensing peak statistics may also possibly provide constraints on the density profile of dark matter halos because massive dark matter halos are the sources of true weak lensing peaks with high signalto-noise ratios (e.g., Yang et al 2013). In our theoretical model of F10, the dependence of the peak abundances on the density profile of dark matter halos is explicit.…”

“…Therefore, in principle, weak lensing peak abundances should reflect the underlying mass function of dark matter halos weighted by the lensing efficiency kernel (e.g., Hamana et al 2004). In practice, however, the correspondence between weak lensing peaks and the massive dark matter halos is influenced by various effects, such as the noise from the intrinsic ellipticities of source galaxies, the projection effect of large-scale structures, and the hierarchical mass distribution of dark matter halos (e.g., van Waerbeke 2000; Tang & Fan 2005;Hamana et al 2012;Yang et al 2013). Thus, it is not straightforward to predict the cosmology dependence of weak lensing peak abundances.…”

A new model to predict weak-lensing peak counts

“…Although we have chosen NFW profiles for the density of DM halos, using any halo profile model for which the projected mass is known is of course possible, such as triaxial halos or profiles offered by baryonic feedback (Yang et al 2013). In addition, our prediction model is completely independent of the method by which peaks are extracted from the WL data.…”

Sample variance in weak lensing: How many simulations are required?

“…In an era where cosmology is data driven, accurate numerical simulations of shear fields are becoming important for several reasons, including assessing baryonic effects [9][10][11][12][13][14], the utility of non-Gaussian statistics [15][16][17][18][19][20][21][22][23] and various systematic effects [24][25][26][27].…”