Exploring the thermal energy contents of the intergalactic mediumwith the Sunyaev–Zeldovich effect

Abstract

We examine the thermal energy contents of the intergalactic medium (IGM) over three orders of magnitude in both mass density and gas temperature using thermal Sunyaev–Zeldovich effect (tSZE). The analysis is based on Planck tSZE map and the cosmic density field, reconstructed in the Sloan Digital Sky Survey Data Release 7 volume and sampled on a grid of cubic cells of |$(1\, h^{-1}{\rm Mpc})^3$|⁠, together with a matched filter technique employed to maximize the signal to noise. Our results show that the pressure–density relation of the IGM is roughly a power law given by an adiabatic equation of state, with an indication of steepening at densities higher than about 10 times the mean density of the Universe. The implied average gas temperature is |$\sim$|104 K in regions of mean density, |$\rho _{\rm m} \sim {\overline{\rho }}_{\rm m}$|⁠, increasing to about |$10^5\, {\rm K}$| for |$\rho _{\rm m} \sim 10\, {\overline{\rho }}_{\rm m}$|⁠, and to |$\gt$|106 K for |$\rho _{\rm m} \sim 100\, {\overline{\rho }}_{\rm m}$|⁠. At a given density, the thermal energy content of the IGM is also found to be higher in regions of stronger tidal fields, likely due to shock heating by the formation of large-scale structure and/or feedback from galaxies and active galactic nuclei. A comparison of the results with hydrodynamic simulations suggests that the current data can already provide interesting constraints on galaxy formation.