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

TL;DR

This study combines X-ray and SZ observations of massive galaxies to constrain the density, temperature, and mass of the hot circumgalactic medium, revealing a shallow density profile and significant baryonic content.

Contribution

It provides the first combined X-ray and SZ analysis of the hot CGM in a large galaxy sample, constraining its density profile and baryonic mass fraction.

Findings

Hot CGM profile ∝ r^{-1.2}, shallower than NFW.

Hot CGM contains 4-30% of galactic baryons within virial radius.

Mass of hot CGM comparable to or exceeding other CGM phases.

Abstract

We use observations of stacked X-ray luminosity and Sunyaev-Zel'dovich (SZ) signal from a cosmological sample of $\sim 80,000$ and $104,000$ massive galaxies, respectively, with $ 10^{12.6}\lesssim M_{500} \lesssim 10^{13} M_{\odot}$ and mean redshift, \={z} $\sim$ 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 ($n_e \propto r^{-3\beta}$) as well as a hydrostatic hot halo model, with the gas assumed to be isothermal in both cases. The datasets are best described by the mean hot CGM profile $\propto r^{-1.2}$, which is shallower than an NFW profile. For halo virial mass $\sim 10^{12}$ - $10^{13} M_{\odot}$, the hot CGM contains $\sim$ 20 - 30\% of galactic baryonic mass for the power-law model and 4 - 11\% for the hydrostatic halo model, within the virial radii. For the power-law model, the hot CGM profile broadly agrees with 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.