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Free keywords:
ACTIVE GALACTIC NUCLEI; GALAXY GROUP FINDER; KILO-DEGREE SURVEY;
STAR-FORMING GALAXIES; LARGE-SCALE STRUCTURE; LAMBDA-CDM UNIVERSE; DATA
RELEASE; PHOTOMETRIC REDSHIFTS; XMM-NEWTON; BARYON BUDGETAstronomy & Astrophysics; galaxies: general; galaxies: halos; galaxies: statistics; X-rays:
galaxies;
Abstract:
Context. 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-*) lower than 3 x 10(11) M-circle dot due to the low surface brightness. Aims. We aim to detect the X-ray emission from the hot CGM around Milky Way-mass (MW-mass, log(M-*/M-circle dot) = 10.5 - 11.0) and M31-mass (log(M-*/M-circle dot) = 11.0 - 11.25) galaxies, in addition to measuring the X-ray surface brightness profile of the hot CGM. Methods. We applied a stacking technique to gain enough statistics to detect the hot CGM. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). We discussed how the satellite galaxies could bias the stacking and the method we used to carefully build the central galaxy samples. Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of z(spec) < 0.2 and stellar masses of 10.0 < log(M-*/M-circle dot) < 11.5 (85 222 galaxies) - or halo masses of 11.5 < log(M-200m/M-circle dot) < 14.0 (125,512 galaxies). By stacking the X-ray emission around galaxies, we obtained the mean X-ray surface brightness profiles. We masked the detected X-ray point sources and carefully modeled 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. Results. We measured the X-ray surface brightness profiles for central galaxies of log(M-*/M-circle dot) > 10.0 or log(M-200m/M-circle dot) > 11.5. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius (R-vir). The signal-to-noise ratio (S/N) of the extended emission around MW-mass (M31-mass) galaxy is about 3.1 sigma (4.7 sigma) within R-vir. We used a beta model to describe the X-ray surface brightness profile of the hot CGM (S-X,S- CGM). We obtained a central surface brightness of log(S-X,S-0[erg s(-1) kpc(-2)]) = 36.7(-0.4)(+1.4) (37.1(-0.4)(+1.5)) and beta = 0.43(-0.06)(+0.10) (0.37(-0.02)(+0.04)) for MW-mass (M31-mass) galaxies. For galaxies with log(M-200m/M-circle dot) > 12.5, the extended X-ray emission is detected with S/N > 2.8 sigma and the S-X,S- CGM can be described by a beta model with beta approximate to 0.4 and log(S-X,S-0[erg s(-1) kpc(-2)]) > 37.2. We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of Lambda CDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within R-vir to larger radii and found that within approximate to 3R(vir), the baryon budget is close to the Lambda CDM cosmology prediction. Conclusions. We measured the extended X-ray emission from representative populations of central galaxies around and above MW-mass out to R-vir. 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.
