Cosmological Studies from Tomographic Weak Lensing Peak Abundances and Impacts of Photo-z Errors

Abstract

Abstract Weak lensing peak abundance analyses have been applied in different surveys and demonstrated to be a powerful statistic in extracting cosmological information complementary to cosmic shear two-point correlation studies. Future large surveys with high number densities of galaxies will enable tomographic peak analyses. Focusing on high peaks, we investigate quantitatively how the tomographic redshift binning can enhance the cosmological gains. We also perform detailed studies about the degradation of cosmological information due to photometric redshift (photo-z) errors. We show that for surveys with a number density of galaxies of ∼40 arcmin−2, a median redshift of ∼1, and a survey area of ∼15,000 deg2, the four-bin tomographic peak analyses can reduce the error contours of (Ωm, σ 8) by a factor of 5 compared to 2D peak analyses in the ideal case of the photo-z error being absent. More redshift bins can hardly lead to significantly better constraints. The photo-z error model here is parameterized by z bias and σ ph and the fiducial values of z bias = 0.003 and σ ph = 0.02 are taken. We find that using tomographic peak analyses can constrain the photo-z errors simultaneously with cosmological parameters. For four-bin analyses, we can obtain σ(z bias)/z bias ∼ 10% and σ(σ ph)/σ ph ∼ 5% without assuming priors on them. Accordingly, the cosmological constraints on Ωm and σ 8 degrade by factors of ∼2.2 and ∼1.8, respectively, with respect to zero uncertainties on photo-z parameters. We find that the uncertainty of z bias plays a more significant role in degrading the cosmological constraints than that of σ ph.