The Hot Gas Halos of Galaxies in Groups

TL;DR

This study uses Chandra X-ray observations to analyze hot gas halos around galaxies in groups, revealing that many retain their hot gas despite environmental stripping processes, with implications for galaxy evolution.

Contribution

It provides the first comprehensive analysis of hot gas halos in group galaxies, showing their prevalence and resilience compared to cluster and field environments.

Findings

~80% of L_K > L_star galaxies have hot gas halos

Higher fraction of bright galaxies in groups retain hot gas compared to clusters

Evidence of ongoing gas stripping via ram pressure and tidal forces

Abstract

We use Chandra observations of 13 nearby groups of galaxies to investigate the hot gas content of their member galaxies. We find that a large fraction of near-IR bright, early-type galaxies in groups have extended X-ray emission, indicating that they retain significant hot gas halos even in these dense environments. In particular, we detect hot gas halos in ~80% of L_K > L_star galaxies. We do not find a significant difference in the L_K-L_X relation for detected group and cluster early-type galaxies. However, we detect X-ray emission from a significantly higher fraction of galaxies brighter than L_star in groups compared to clusters, indicating that a larger fraction of galaxies in clusters experience significant stripping of their hot gas. In addition, group and cluster galaxies appear to be X-ray faint compared to field galaxies, though a Chandra based field sample is needed to confirm this result. The near-IR bright late-types galaxies in clusters and groups appear to follow the L_K-L_X relation for early-type galaxies, while near-IR fainter late-type galaxies are significantly more X-ray luminous than this relation likely due to star formation. Finally, we find individual examples of ongoing gas stripping of group galaxies. One galaxy shows a 40-50 kpc X-ray tail, and two merging galaxy systems show tidal bridges/tails of X-ray emission. Therefore, stripping of hot galactic gas through both ram pressure and tidal forces does occur in groups and clusters, but the frequency or efficiency of such events must be moderate enough to allow hot gas halos in a large fraction of bright galaxies to survive even in group and cluster cores.