The thermal and gravitational energy densities in the large-scale structure of the Universe
Abstract
As cosmic structures form, matter density fluctuations collapse gravitationally and baryonic matter is shock-heated and thermalized. We therefore expect a connection between the mean gravitational potential energy density of collapsed halos, W halo, and the mean thermal energy density of baryons, th. These quantities can be obtained using two fundamentally different estimates: we compute W halo using the theoretical framework of the halo model which is driven by dark matter statistics, and measure th using the Sunyaev-Zeldovich (SZ) effect which probes the mean thermal pressure of baryons. First, we derive that, at the present time, about 90% of W halo originates from massive halos with M>1013\,M. Then, using our measurements of the SZ background, we find that th accounts for about 80% of the kinetic energy of the baryons available for pressure in halos at z 0.5. This constrains the amount of non-thermal pressure, e.g., due to bulk and turbulent gas motion sourced by mass accretion, to be about non-th 0.4× 10-8 at z=0.