X-ray metal line emission from the hot circumgalactic medium: probing the effects of supermassive black hole feedback

TL;DR

This study uses advanced cosmological simulations to predict X-ray emission from the hot circumgalactic medium, revealing how supermassive black hole feedback influences its distribution and properties, and discusses prospects for observational testing.

Contribution

It compares three leading galaxy simulations to analyze the spatial and azimuthal distribution of X-ray metal line emission in the CGM, highlighting SMBH feedback effects.

Findings

Different simulations predict varying surface brightness profiles.

Star-forming galaxies are X-ray brighter than quiescent ones.

Anisotropic X-ray emission patterns suggest SMBH-driven outflows.

Abstract

We derive predictions from state-of-the-art cosmological galaxy simulations for the spatial distribution of the hot circumgalactic medium (CGM, ${\rm [0.1-1]R_{200c}}$) through its emission lines in the X-ray soft band ($[0.3-1.3]$ keV). In particular, we compare IllustrisTNG, EAGLE, and SIMBA and focus on galaxies with stellar mass $10^{10-11.6}\, \MSUN$ at $z=0$. The three simulation models return significantly different surface brightness radial profiles of prominent emission lines from ionized metals such as OVII(f), OVIII, and FeXVII as a function of galaxy mass. Likewise, the three simulations predict varying azimuthal distributions of line emission with respect to the galactic stellar planes, with IllustrisTNG predicting the strongest angular modulation of CGM physical properties at radial range ${\gtrsim0.3-0.5\,R_{200c}}$. This anisotropic signal is more prominent for higher-energy lines, where it can manifest as X-ray eROSITA-like bubbles. Despite different models of stellar and supermassive black hole (SMBH) feedback, the three simulations consistently predict a dichotomy between star-forming and quiescent galaxies at the Milky-Way and Andromeda mass range, where the former are X-ray brighter than the latter. This is a signature of SMBH-driven outflows, which are responsible for quenching star formation. Finally, we explore the prospect of testing these predictions with a microcalorimeter-based X-ray mission concept with a large field-of-view. Such a mission would probe the extended hot CGM via soft X-ray line emission, determine the physical properties of the CGM, including temperature, from the measurement of line ratios, and provide critical constraints on the efficiency and impact of SMBH feedback on the CGM.