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 HSC, DES and LSST, the best-fit value of
the non-Gaussian parameter, fNL, obtained from the galaxy count data is highly
biased, and the true values of fNL 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 fNL would
become small enough compared to the expected 1-sigma error for HSC and DES, but
it would be still serious for deep surveys with z_m > 1.5, like LSST.
Tomographic technique improves the constraint on fNL by a factor of 2-3
compared to the one without tomography, but the systematic bias would increase.
