Chandra survey of nearby highly inclined disk galaxies -- V: emission structure and origin of galactic coronae

TL;DR

This study analyzes the morphology of X-ray coronae around nearby disk galaxies to understand their origins, revealing two components influenced by star formation activity and cool-hot gas interactions.

Contribution

It introduces model-independent vertical scale parameters and correlates them with galaxy properties to distinguish hot gas outflows from cool gas interactions.

Findings

Weak negative correlation between vertical scale and star formation rate.

Strong negative correlation of emission concentration with star formation rate.

Evidence for two components: hot gas outflows and cool gas interactions.

Abstract

The origin of the extended soft X-ray emission around nearby highly inclined disk galaxies (often called as X-ray corona) remains uncertain. The emission could arise from volume-filling hot gas and/or its interaction with cool gas. Morphological properties of the X-ray emission can provide additional information to distinguish these different origins. We define model-independent parameters H50, H75, and H95 - vertical scales that enclose 50%, 75%, and 95% of the total flux of the emission, respectively. We study the correlation of these parameters with galaxy properties inferred from infrared observations of a sample of nearby highly inclined disk galaxies with high-quality Chandra data. We find weak negative correlations between H50or H75and the surface star formation rate (ISFR) and no correlation for H95. However, we detect strong, negative correlations of the vertical concentration of the emission, defined as H50/H95 or H75/H95, with ISFR. Our findings suggest that the X-ray emission around disk galaxies is likely comprised of two components: the extended, weak emission, characterized by H95, is influenced by the outflowing hot gas entrained in star formation driven winds, whereas the strong emission close to the disk which is often rich in cool gas characterized by H50 or H75, is largely impacted by cool-hot gas interaction.