Semi-Analytic Galaxy Formation in Massive Neutrino Cosmologies

The constraints on neutrino masses led to the revision of their cosmological role, since the existence of a cosmological neutrino background is a clear prediction of the standard cosmological model. In this paper, we study the impact of such background on the spatial distribution of both Dark Matter (DM) and galaxies, by coupling $N$-body numerical simulations with semi-analytic models (SAMs) of galaxy formation. Cosmological simulations including massive neutrinos predict a slower evolution of DM perturbations with respect to the $Λ$CDM runs with the same initial conditions and a suppression on the matter power spectrum on small and intermediate scales, thus impacting on the predicted properties of galaxy populations. We explicitly show that most of these deviations are driven by the different $σ_8$ predicted for cosmologies including a massive neutrino background. We conclude that independent estimates of $σ_8$ are needed, in order to unambiguously characterise the effect of this background on the growth of structures. Galaxy properties alone are a weak tracer of deviations with respect to the $Λ$CDM run, but their combination with the overall matter distribution at all scales allows to disentangle between different cosmological models. Moreover, these deviations go on opposite direction with respect to competing models like modified gravity, thus weakening any detectable cosmological signal. Given the ubiquitous presence of a neutrino background, these effects have to be taken into account in future missions aimed at constraining the properties of the "Dark" components of the Universe.

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