It is a well known fact that galaxies are biased tracers of the distribution of matter in the Universe. The galaxy bias is usually factored as a function of redshift and scale, and approximated as being scale-independent on large, linear scales. In cosmologies with massive neutrinos, the galaxy bias defined with respect to the total matter field (cold dark matter, baryons, and non-relativistic neutrinos) also depends on the sum of the neutrino masses Mν, and becomes scale-dependent even on large scales. This effect has been usually neglected given the sensitivity of current surveys. However, it becomes a severe systematic for future surveys aiming to provide the first detection of non-zero Mν. The effect can be corrected for by defining the bias with respect to the density field of cold dark matter and baryons, rather than the total matter field. In this work, we provide a simple prescription for correctly mitigating the neutrino-induced scale-dependent bias effect in a practical way. We clarify a number of subtleties regarding how to properly implement this correction in the presence of redshift-space distortions and non-linear evolution of perturbations. We perform a Markov Chain Monte Carlo analysis on simulated galaxy clustering data that match the expected sensitivity of the Euclid survey. We find that the neutrino-induced scale-dependent bias can lead to important shifts in both the inferred mean value of Mν, as well as its uncertainty, and provide an analytical explanation for the magnitude of the shifts. We show how these shifts propagate to the inferred values of other cosmological parameters correlated with Mν, such as the cold dark matter physical density Ωcdm h2 and the scalar spectral index ns. In conclusion, we find that correctly accounting for the neutrino-induced scale-dependent bias will be of crucial importance for future galaxy clustering analyses. We encourage the cosmology community to correctly account for this effect using the simple prescription we present in our work. The tools necessary to easily correct for the neutrino-induced scale-dependent bias will be made publicly available in an upcoming release of the Boltzmann solver CLASS.
Journal of Cosmology and Astroparticle Physics
- Pub Date:
- September 2018
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- High Energy Physics - Phenomenology
- 12 pages, 2 figures, abstract abridged. Version accepted for publication in JCAP. The busy reader should skip to Sec. IID, V, and the figures. A "Note added" between conclusions and acknowledgements explains our choice of title