Detection of cosmic magnification via galaxy shear-galaxy number density correlation from HSC survey data

Abstract

We propose a novel method to detect cosmic magnification signals by cross-correlating foreground convergence fields constructed from galaxy shear measurements with background galaxy positional distributions---namely, shear-number density correlation. We apply it to the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey data. With 27 nonindependent data points and their full covariance, ${\ensuremath{\chi}}_{0}^{2}\ensuremath{\approx}34.1$ and ${\ensuremath{\chi}}_{T}^{2}\ensuremath{\approx}24.0$ with respect to the null and the cosmological model with the parameters from HSC shear correlation analyses in Hamana et al. [Publ. Astron. Soc. Jpn. 72, 16 (2020)], respectively. The Bayes factor of the two is ${\mathrm{log}}_{10}{B}_{T0}\ensuremath{\approx}2.2$ assuming equal model probabilities of null and HSC cosmology, showing a clear detection of the magnification signals. Theoretically, the ratio of the shear-number density and shear-shear correlations can provide a constraint on the effective multiplicative shear bias $\overline{m}$ using internal data themselves. We demonstrate the idea with the signals from our HSC-SSP mock simulations and rescale the statistical uncertainties to a survey of $15000\text{ }\text{ }{\mathrm{deg}}^{2}$. For two-bin analyses with background galaxies brighter than ${m}_{\mathrm{lim}}=23$, the combined analyses lead to a forecasted constraint of $\ensuremath{\sigma}(\overline{m})\ensuremath{\sim}0.032$, 2.3 times tighter than that found when using the shear-shear correlation alone. Correspondingly, $\ensuremath{\sigma}({S}_{8})$ with ${S}_{8}={\ensuremath{\sigma}}_{8}({\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}/0.3{)}^{0.5}$ is tightened by $\ensuremath{\sim}2.1$ times. Importantly, the joint constraint on $\overline{m}$ is nearly independent of cosmological parameters. Our study therefore points to the importance of including the shear-number density correlation in weak lensing analyses, which can provide valuable consistency tests of observational data, and thus to solidify the derived cosmological constraints.

Topics & Concepts