Scale-dependent halo bias and the squeezed limit bispectrum in the presence of radiation
Abstract
We investigate the gravitational effect of large-scale radiation perturbations on small-scale structure formation. In addition to making the growth of matter perturbations scale dependent, the free-streaming of radiation also affects the coupling between structure formation at small and large scales. We study this using Separate Universe N-body simulations to compute the (isotropized) squeezed-limit matter bispectrum and the linear halo bias. Our results show that the scale dependence in the growth of long-wavelength matter perturbations, caused by radiation, translates into these quantities acquiring a non-trivial scale-dependence at k 0.05 Mpc-1. In a universe with radiation composed of cosmic microwave background photons and three species of massless neutrinos, the bias of halos with b = 2 at high k will decrease by 0.29\%,\ 0.45\% and 0.8\% between k = 0.05 Mpc-1 and k = 0.0005 Mpc-1 at redshifts z=0,\ 1, and 3 respectively. For objects with b1, these differences approach 0.43\%,\ 0.68\% and 1.2\% respectively.