X-ray and SZ constraints on the properties of hot CGM

Abstract

We use observations of stacked X-ray luminosity and Sunyaev-Zel'dovich (SZ) signal from a cosmological sample of ~80 000 and 104 000 massive galaxies, respectively, with 1012.6 ≲ M500 ≲ 1013 M⊙ and mean redshift, z ~ 0.1-0.14 to constrain the hot circumgalactic medium (CGM) density and temperature. The X-ray luminosities constrain the density and hot CGM mass, while the SZ signal helps in breaking the density-temperature degeneracy. We consider a simple power-law density distribution (ne ∝ r-3β) as well as a hydrostatic hot halo model, with the gas assumed to be isothermal in both cases. The data sets are best described by the mean hot CGM profile ∝ r-1.2, which is shallower than an NFW profile. For halo virial mass ~1012-1013 M⊙, the hot CGM contains ~ 20-30 per cent of galactic baryonic mass for the power-law model and 4-11 per cent for the hydrostatic halo model, within the virial radii. For the power-law model, the hot CGM profile broadly agrees with the observations of the Milky Way. The mean hot CGM mass is comparable to or larger than the mass contained in other phases of the CGM for L* galaxies.