Detection of Anisotropies in the Circumgalactic Medium of Disk Galaxies: Supermassive Black Hole Activity or Star Formation-driven Outflows?

TL;DR

This study analyzes X-ray emissions from the circumgalactic medium of 93 nearby galaxies, revealing anisotropies linked to star formation or black hole activity, and compares observations with simulations to understand bubble origins.

Contribution

It provides the first stacked X-ray analysis of CGM in a large galaxy sample, identifying anisotropies associated with star formation and black hole activity, and compares these with cosmological simulations.

Findings

Detected diffuse X-ray emission extending up to 14 kpc.

Found significant anisotropies along the galactic minor axis in high star formation galaxies.

Observed bubbles are smaller than those predicted by simulations, suggesting different driving mechanisms.

Abstract

Gamma and X-ray observatories have revealed spectacular structures in the emission of the tenuous hot gas surrounding the Milky Way (MW), known as the Fermi and eROSITA bubbles. Galaxy formation simulations suggest that MW-like bubbles could be ubiquitous, but their emission may be too faint to detect with today's instruments in individual external galaxies. In this paper, we present an analysis of stacked Chandra observations of 93 nearby galaxies. We detected soft, diffuse X-rays from the CGM, extending up to 14 kpc, with a luminosity of $(4.2\pm0.7)\times10^{39}$ erg/s in the $0.3-2$ keV band. To probe its spatial distribution, we constructed an azimuthal profile and found a significant enhancement along the galactic minor axis. When dividing our sample by stellar mass, central supermassive black hole mass, and star formation rate, we found that only high star formation rate galaxies exhibit significant anisotropies in the CGM emission. To investigate whether the observed anisotropies could be attributed to MW-like bubbles, we compared our results with TNG50 simulations. In these simulations, X-ray bubbles are strongly correlated with mass of the central supermassive black hole and typically extend to much larger, $\sim50$ kpc, scales. We conclude that the observed anisotropies are either caused by AGN-driven MW-like bubbles confined to smaller, $\sim10$ kpc, scales, or by star formation- or starburst-driven bubbles/outflows.