Constraints on the Hot Circumgalactic Medium around Nearby L* Galaxies from SRG/eROSITA All Sky Survey

TL;DR

This study uses SRG/eROSITA X-ray data to detect and analyze the hot circumgalactic medium around nearby L* galaxies, providing new constraints that align with cosmological simulations and inform galaxy evolution models.

Contribution

First systematic search of hot CGM around nearby L* galaxies using stacking of eROSITA X-ray data, revealing diffuse hot gas consistent with simulations.

Findings

Diffuse X-ray emission detected out to ~50 kpc

Spectral signatures indicate hot gas, not non-thermal processes

Hot gas distribution matches IllustrisTNG simulation predictions

Abstract

The circumgalactic medium (CGM) is a multi-phase, dynamic interface between galaxy and the intergalactic medium, providing crucial diagnostics of galaxy evolution. However, direct evidence for a hot (million-Kelvin) CGM around present-day L* galaxies remains elusive. Here, we present the first systematic search of the hot CGM around nearby (< 50 Mpc) L* galaxies, by stacking their X-ray images and spectra from the SRG/eROSITA all-sky survey. Significant diffuse X-ray emission is detected out to ~ 50 kpc, with spectral signatures consistent with a hot gas but arguing against a predominantly non-thermal origin. The radial distribution and total amount of the hot gas are in agreement with prediction by IllustrisTNG simulations. The constraints on the hot CGM derived in this study hold promise for calibrating key physical processes in next-generation cosmological simulations.