Galaxy clusters as cosmological probes: the impact of baryonic physics. (arXiv:1210.4117v1 [astro-ph.CO])

Galaxy clusters as cosmological probes: the impact of baryonic physics. (arXiv:1210.4117v1 [astro-ph.CO]):
The halo mass function from N-body simulations of collisionless matter is
generally used to retrieve cosmological parameters from observed counts of
galaxy clusters. This neglects the observational fact that the baryonic mass
fraction in clusters is a random variable that, on average, increases with the
total mass. Considering a mock catalog that includes tens of thousands of
galaxy clusters, as expected from the forthcoming generation of surveys, we
show that the effect of a varying baryonic mass fraction will be observable
with high statistical significance. The net effect is a change in the overall
normalization of the cluster mass function and a milder modification of its
shape. Our results indicate the absolute necessity of taking into account
baryonic corrections to the mass function if one wants to obtain unbiased
estimates of the cosmological parameters from data of this quality. We
introduce the formalism necessary to accomplish this goal. Our discussion is
based on the conditional probability of finding a given value of the baryonic
mass fraction for clusters of fixed total mass. Finally, we show that combining
information from the cluster counts with measurements of the baryonic mass
fraction in a small subsample of clusters (including only a few tens of
objects) will nearly optimally constrain the cosmological parameters.