A Spitzer Space Telescope Atlas of omega Centauri: The Stellar Population, Mass Loss, and the Intracluster Medium

TL;DR

This study uses Spitzer imaging to analyze stellar mass loss and the intracluster medium in omega Centauri, revealing dust production by evolved stars and faint diffuse emissions possibly indicating escaping intracluster material.

Contribution

First comprehensive infrared survey of omega Centauri linking stellar mass loss to intracluster medium properties at low metallicity.

Findings

Approximately 140 cluster members show 24 micron excess indicating dust.

Estimated mass loss rate is 2.9-4.2 x 10^(-7) solar masses per year.

Detected faint diffuse emission regions possibly representing escaping intracluster dust.

Abstract

We present a Spitzer Space Telescope imaging survey of the most massive Galactic globular cluster, omega Centauri, and investigate stellar mass loss at low metallicity and the intracluster medium (ICM). The survey covers approximately 3.2x the cluster half-mass radius at 3.6, 4.5, 5.8, 8, and 24 microns, resulting in a catalog of over 40,000 point-sources in the cluster. Approximately 140 cluster members ranging 1.5 dex in metallicity show a red excess at 24 microns, indicative of circumstellar dust. If all of the dusty sources are experiencing mass loss, the cumulative rate of loss is estimated at 2.9 - 4.2 x 10^(-7) solar masses per year, 63% -- 66% of which is supplied by three asymptotic giant branch stars at the tip of the Red Giant Branch (RGB). There is little evidence for strong mass loss lower on the RGB. If this material had remained in the cluster center, its dust component (> 1 x 10^(-4) solar masses) would be detectable in our 24 and 70 micron images. While no dust cloud located at the center of omega Cen is apparent, we do see four regions of very faint, diffuse emission beyond two half-mass radii at 24 microns. It is unclear whether these dust clouds are foreground emission or are associated with omega Cen. In the latter case, these clouds may be the ICM in the process of escaping from the cluster.