Detection of Hot Gas in Galaxy Groups via the Sunyaev-Zel'dovich Effect

Abstract

Motivated by the observed shortfall of baryons in the local universe, we investigate the ability of high resolution cosmic microwave background (CMB) experiments to detect hot gas in the outer regions of nearby group halos. We construct hot gas models with the gas in hydrostatic equilibrium with the dark matter and described by a polytropic equation of state. We also consider models that add entropy to the gas in line with constraints from X-ray observations. We calculate the thermal Sunyaev-Zel'dovich (SZ) signal in these halos and compare it to the anticipated sensitivities of forthcoming SZ survey experiments such as ACT, PLANCK and SPT. Using a multi-frequency Wiener filter we derive SZ detectability limits as a function of halo mass and redshift in the presence of galactic and extragalactic foregrounds and the CMB. We find that group-sized halos with virial masses below 1e14 M_solar can be detected at z < 0.05 with the threshold mass dropping to 3-4e13 M_solar at z < 0.01. The SZ distortion of nearby group-sized halos can thus be mapped out to the virial radius by these CMB experiments, beyond the sensitivity limits of X-ray observations. These measurements will provide a unique probe of hot gas in the outer regions of group halos, shedding insight into the local census of baryons and the injection of entropy into the intragroup medium from non-gravitational feedback.