The imprint of neutrinos on clustering in redshift-space

Abstract

(abridged) We investigate the signatures left by the cosmic neutrino background on the clustering of matter, CDM+baryons and halos in redshift-space using a set of more than 1000 N-body and hydrodynamical simulations with massless and massive neutrinos. We find that the effect neutrinos induce on the clustering of CDM+baryons in redshift-space on small scales is almost entirely due to the change in $\ddot{I}{ƒ}_8$. Neutrinos imprint a characteristic signature in the quadrupole of the matter (CDM+baryons+neutrinos) field on small scales, that can be used to disentangle the effect of $\ddot{I}{ƒ}_8$ and $M_{\hat{I}}½$. We show that the effect of neutrinos on the clustering of halos is very different, on all scales, to the one induced by $\ddot{I}{ƒ}_8$. We find that the effects of neutrinos of the growth rate of CDM+baryons ranges from $\sim 0.3\%$ to $2\%$ on scales $k\in [0.01,0.5]h{\mathrm{Mpc}}^{-1}$ for neutrinos with masses $M_{\hat{I}}½⩽0.15$ eV. We compute the bias between the momentum of halos and the momentum of CDM+baryon and find it to be 1 on large scales for all models with massless and massive neutrinos considered. This point towards a velocity bias between halos and total matter on large scales that it is important to account for in order to extract unbiased neutrino information from velocity/momentum surveys such as kSZ observations. We show that baryonic effects can affect the clustering of matter and CDM+baryons in redshift-space by up to a few percent down to $k=0.5h{\mathrm{Mpc}}^{-1}$. We find that hydrodynamics and astrophysical processes, as implemented in our simulations, only distort the relative effect that neutrinos induce on the anisotropic clustering of matter, CDM+baryons and halos in redshift-space by less than $1\%$. Thus, the effect of neutrinos in the fully non-linear regime can be written as a transfer function with very weak dependence on astrophysics.

19 pages, 12 figures