The Hot Circum-Galactic Medium in the eROSITA All Sky Survey I. X-ray Surface Brightness Profiles

We apply a stacking technique to gain enough statistics to detect the hot CGM around galaxies. We use the X-ray data from the first four SRG/eROSITA all-sky surveys (eRASS:4). We discuss how the satellite galaxies could bias the stacking and carefully build the central galaxy samples based on the SDSS spectroscopic survey and halo-based group finder algorithm and isolated galaxy sample from the ninth data release of the DESI Legacy survey (LS DR9, photometric). We mask the detected X-ray point sources and carefully model the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB) to obtain the X-ray emission from the hot CGM. The X-ray surface brightness profiles are measured for log(M_*)>10.0 or log(M_ 200m)>11.5 central galaxies, and log(M_*)>9.5 isolated galaxies. We detect the X-ray emission around MW-mass (log(M_*)=10.5-11.0) and more massive central galaxies extending up to the virial radius (R_ vir). The signal-to-noise ratio of the extended emission around the MW-mass galaxy is about 8.1σ within R_ vir. We use the β model to describe the X-ray surface brightness profiles of the hot CGM. We obtain a central surface brightness of S_ X,0≈ 3.1×10^35 erg/s/kpc^2 and β≈0.42 for MW-mass galaxy. We estimate the baryon budget of the hot CGM and obtain a value lower than the Λ CDM cosmology predicted. Our results set a firm footing for the presence of a hot CGM around MW-mass and more massive central galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.