The hot circumgalactic medium in the eROSITA All-Sky Survey I. X-ray surface brightness profiles

Abstract

The circumgalactic medium (CGM) provides the material needed for galaxy formation and influences galaxy evolution. The hot ($T>10^{6}K$) CGM is poorly detected around galaxies with stellar masses ($M_{\ast }$) lower than $3\times 10^{11}{M}_{\odot }$ due to the low surface brightness. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of $z_{\mathrm{spec}}<0.2$ and stellar masses of $10.0<\log (M_{\ast }/M_{\odot })<11.5$ (85,222 galaxies) -- or halo masses of $11.5<\log (M_{200m}/M_{\odot })<14.0$ (125,512 galaxies). By stacking the X-ray emission around galaxies, masking the detected X-ray point sources and carefully modeling the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB), we obtain the X-ray emission from the hot CGM. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius ($R_{\mathrm{vir}}$). We used a ${\hat{I}}^2$ model to describe the X-ray surface brightness profile and found ${\hat{I}}^2=0.43_{-0.06}^{+0.10}(0.37_{-0.02}^{+0.04})$ for MW-mass (M31-mass) galaxies.We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of $\hat{I}›$CDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within $R_{\mathrm{vir}}$ to larger radii and found that within $\approx 3R_{\mathrm{vir}}$, the baryon budget is close to the $\hat{I}›$CDM cosmology prediction. Our results set a firm footing for the presence of the hot CGM around such galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.

Abstract abridged for arXiv submission, accepted by A&A