The fundamental plane of gamma-ray globular clusters

Abstract

We have investigated the properties of a group of γ-ray-emitting globular clusters (GCs) that have recently been uncovered in our Galaxy. By correlating the observed γ-ray luminosity Lγwith various cluster properties, we probe the origin of the high-energy photons from these GCs. We report that Lγis positively correlated with the encounter rate Ãc and the metallicity [Fe/H], which places an intimate link between the γ-ray emission and the millisecond-pulsar population. We also find a tendency that Lγincreases with the energy densities of the soft photon at the cluster location. Furthermore, the two-dimensional regression analysis suggests that Lγ, soft-photon densities, and Ãc/[Fe/H] possibly span fundamental planes; this finding could potentially provide better predictions for the γ-ray properties of GCs. © 2011 The American Astronomical Society. All rights reserved.