The hot circumgalactic medium in the eROSITA All-Sky Survey

III. Star-forming and quiescent galaxies

¹ Max-Planck-Institut für extraterrestrische Physik (MPE), Gießenbachstraße 1, D-85748 Garching bei München, Germany
² INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy
³ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁴ Center for Space Sciences and Technology, University of Maryland, 1000 Hilltop Circle, Baltimore, MD 21250, USA
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ European Southern Observatory, Karl Schwarzschildstrasse 2, D-85748 Garching bei München, Germany
⁷ Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
⁸ School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China
⁹ Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany

^⋆ Corresponding author; yizhang@mpe.mpg.de

Received: 17 September 2024
Accepted: 27 November 2024

Abstract

Aims The galaxy population shows a characteristic bimodal distribution based on the star formation activity and is sorted into star-forming or quiescent. These two subpopulations have a tendency to be located in different mass halos. The circumgalactic medium (CGM), as the gas repository for star formation, might contain the answer to the mystery of the formation of such bimodality. Here we consider the bimodality of the galaxy population and study the difference between the properties of the hot CGM around star-forming and quiescent galaxies.

Methods. We used the X-ray data from the first four SRG/eROSITA all-sky surveys (eRASS:4). We selected central star-forming and quiescent galaxies from the Sloan Digital Sky Survey DR7 with stellar mass 10.0 < log(M_*/M_⊙) < 11.5 or halo mass 11.5 < log(M_200 m/M_⊙) < 14.0 within spectroscopic redshift z_spec < 0.2, and we built approximately volume-limited galaxy samples. We stacked the X-ray emission around star-forming and quiescent galaxies, respectively. We masked detected point sources and carefully modeled the X-ray emission from unresolved active galaxy nuclei (AGN) and X-ray binaries (XRB) to detect the X-ray emission from the hot CGM. We measured the X-ray surface brightness (S_X, CGM) profiles and integrated the X-ray emission from hot CGM within R_500c (L_X, CGM) to provide the scaling relations between L_X, CGM and galaxies’ stellar or halo mass.

Results. We detect extended X-ray emission from the hot CGM around star-forming galaxies with log(M_*/M_⊙) > 11.0 and quiescent galaxies with log(M_*/M_⊙) > 10.5, extending out to R_500c. The S_X, CGM profile of quiescent galaxies follows a β model with β ≈ 0.4, where β quantifies the slope of the profile. Star-forming galaxies with median stellar masses log(M_*, med/M_⊙) = 10.7, 11.1, 11.3 have L_X, CGM ≈ 0.8,  2.3,  4.0 × 10⁴⁰ erg/s, while for quiescent galaxies with log(M_*, med/M_⊙) = 10.8, 11.1, 11.4, L_X, CGM ≈ 1.1,  6.2,  30 × 10⁴⁰ erg/s. Notably, quiescent galaxies with log(M_*, med/M_⊙) > 11.0 exhibit brighter hot CGM than their star-forming counterparts. In halo mass bins, we detect similar X-ray emission around star-forming and quiescent galaxies with log(M_200 m/M_⊙) > 12.5, suggesting that galaxies in the same mass dark matter halos host equally bright hot CGM. We emphasize that the observed L_X, CGM − M_500c relations of star-forming and quiescent galaxies are sensitive to the stellar-to-halo mass relation (SHMR). A comparison with cosmological hydrodynamical simulations (EAGLE, TNG100, and SIMBA) reveals varying degrees of agreement, contingent on the simulation and the specific stellar or halo mass ranges considered.

Conclusions. Either selected in stellar mass or halo mass, the star-forming galaxies do not host brighter stacked X-ray emission from the hot CGM than their quiescent counterparts at the same mass range. The result provides useful constraints on the extent of feedback’s impacts as a mechanism for quenching star formation as implemented in current cosmological simulations.