Extended Hot Halos Around Isolated Galaxies Observed in the ROSAT All-Sky Survey

TL;DR

This study detects and characterizes hot X-ray emitting gas halos around isolated galaxies, providing constraints on their luminosity, extent, and mass, with implications for galaxy evolution and gas accretion.

Contribution

It presents the first systematic analysis of hot gas halos around isolated galaxies using ROSAT data, quantifying their luminosity, extent, and mass.

Findings

Detected X-ray emission in all galaxy subsamples with high confidence.

Found evidence for extended hot gas emission around most subsamples.

Estimated hot gas mass of about 4 billion solar masses within 50 kpc.

Abstract

We place general constraints on the luminosity and mass of hot X-ray emitting gas residing in extended "hot halos" around nearby massive galaxies. We examine stacked images of 2165 galaxies from the 2MASS Very Isolated Galaxy Catalog (2MVIG), as well as subsets of this sample based on galaxy morphology and K-band luminosity. We detect X-ray emission at high confidence (ranging up to nearly 10\sigma) for each subsample of galaxies. The average L_X within 50 kpc is 1.0\pm0.1 (statistical) \pm0.2 (systematic) x10^40 erg/s, although the early-type galaxies are more than twice as luminous as the late-type galaxies. Using a spatial analysis, we also find evidence for extended emission around five out of seven subsamples (the full sample, the luminous galaxies, early-type galaxies, luminous late-type galaxies, and luminous early-type galaxies) at 92.7%, 99.3%, 89.3%, 98.7%, and 92.1% confidence, respectively. Several additional lines of evidence also support this conclusion and suggest that about 1/2 of the total emission is extended, and about 1/3 of the extended emission comes from hot gas. For the sample of luminous galaxies, which has the strongest evidence for extended emission, the average hot gas mass is 4x10^9 Msun within 50 kpc and the implied accretion rate is 0.4 Msun/yr.