Precision reconstruction of the cold dark matter-neutrino relative velocity.

Abstract

Neutrinos occur in great number throughout the Universe, yet remain poorly understood due to their weak interactions with other matter. In particular, individual neutrino masses remain an elusive property for particle physicists and cosmologists abound. Recently, it has been proposed that individual neutrino masses may be constrained from observations of neutrino wakes that result from the relative flow between cold dark matter (CDM) and neutrinos. The only required knowledge for such a detection is the relative velocity field between CDM and neutrinos. However, since neither CDM nor neutrinos are directly observable, their relative flow must be obtained by indirect means. We modify the cosmology code, CUBEP3M, to simulate neutrino N-body particles alongside CDM. We find the result that the relative velocity field can be obtained accurately by applying linear transformations to the halo density field. Assuming prior knowledge of the halo bias, we find that the reconstructed relative velocities are highly correlated with the simulated ones, with correlation coefficients of 0.94, 0.93, 0.92 and 0.88 for neutrinos of mass 0.05, 0.1, 0.2 and 0.4 eV, respectively. We confirm that the relative velocity field reconstructed from large-scale structure observations, such as galaxy or 21 cm surveys, can be accurate in direction and, with appropriate scaling, magnitude.