Magnification effect on the detection of primordial non-Gaussianity from photometric surveys

We present forecast results for constraining the primordial non-Gaussianity from photometric surveys through a large-scale enhancement of the galaxy clustering amplitude. In photometric surveys, the distribution of observed galaxies at high redshifts suffers from the gravitational-lensing magnification, which systematically alters the number density for magnitude-limited galaxy samples. We estimate size of the systematic bias in the best-fit cosmological parameters caused by the magnification effect, particularly focusing on the primordial non-Gaussianity. For upcoming deep and/or wide photometric surveys like the Hyper Suprime-Cam, the Dark Energy Survey and the Large Synaptic Survey Telescope, the best-fit value of the non-Gaussian parameter, f(NL), obtained from the galaxy count data is highly biased, and the true values of f(NL) would typically go outside the 3-sigma error of the biased confidence region, if we ignore the magnification effect in the theoretical template of angular power spectrum. The additional information from cosmic shear data helps not only to improve the constraint, but also to reduce the systematic bias. As a result, the size of systematic bias on f(NL) would become small enough compared to the expected 1-sigma error for the Hyper Suprime-Cam and the Dark Energy Survey, but it would still be serious for deep surveys with z(m) greater than or similar to 1.5, like the Large Synaptic Survey Telescope. Tomographic technique improves the constraint on f(NL) by a factor of 2-3 compared to the one without tomography, but the systematic bias would increase.