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 $k\lesssim 0.05$ 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 $b\gg 1$, these differences approach $0.43\%,0.68\%$ and $1.2\%$ respectively.

11 pages, 13 figures

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Cited by in corpus (1)

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