The hot circumgalactic medium in stacked X-rays: observations vs simulations

TL;DR

This study compares observed and simulated X-ray emissions from the circumgalactic medium to evaluate and improve models of active galactic nuclei feedback in galaxy formation simulations.

Contribution

It introduces synthetic eROSITA observations from EAGLE and SIMBA simulations and assesses their agreement with actual observations across various galaxy properties.

Findings

SIMBA better matches observed surface brightness profiles than EAGLE.

Differences in X-ray emission are mainly due to density variations at small radii.

Temperature and metallicity differences influence emission at larger radii.

Abstract

Current cosmological simulations rely on active galactic nuclei (AGN) feedback to quench star formation and match observed stellar mass distributions, but models for AGN feedback are poorly constrained. The circumgalactic medium (CGM) provides a valuable laboratory to study this process, as its metallicity, temperature, and density distributions are directly shaped by AGN activity. Recent observations from the eROSITA instrument provide constraints on the CGM through measurements of extended soft X-ray emission. In this work, we generate synthetic eROSITA observations from the EAGLE and SIMBA cosmological simulations and compare them to observations of galaxies stacked by stellar mass, halo mass, and star-formation rate. SIMBA outperforms EAGLE in matching observed surface brightness profiles, but neither simulation achieves consistent agreement with observations across the full range of galaxy properties we studied. We find that variations in CGM X-ray emission between simulations are primarily driven by density differences at $R \lesssim 0.2 R_{200c} $, and temperature and metallicity changes at larger radii. These results highlight the need for further refinement of AGN feedback models in cosmological simulations and demonstrate the power of stacked X-ray observations as a tool for constraining feedback physics.