The Low Mass X-ray Binary - Globular Cluster Link and its Implications

TL;DR

This paper explores the strong link between low mass X-ray binaries and globular clusters, highlighting the influence of metallicity and the implications for galaxy formation theories.

Contribution

It provides new evidence of metallicity variations within metal-rich globular clusters and discusses the reliability of correlations between cluster properties and LMXB presence.

Findings

LMXBs are predominantly found in metal-rich globular clusters.

There is no clear correlation between LMXBs and cluster age.

Metallicity variations within the metal-rich peak are supported by LMXB distribution patterns.

Abstract

Studies of nearby elliptical and S0 galaxies reveal that roughly half of the low mass X-ray binaries (LMXBs), which are luminous tracers of accreting neutron star or black hole systems, are in clusters. There is a surprising tendency of LMXBs to be preferentially associated with metal-rich globular clusters (GCs), with metal-rich GCs hosting three times as many LMXBs as metal-poor ones. There is no convincing evidence of a correlation with GC age so far. In some galaxies the LMXB formation rate varies with GC color even within the metal-rich peak of the typical bimodal cluster metallicity distribution. This provides some of the strongest evidence to date that there are metallicity variations within the metal-rich GC peak, as is expected in hierarchical galaxy formation scenarios. We also note that apparent correlations between the interaction rates in GCs and LMXB frequency may not be reliable because of the uncertainties in some GC parameters. We argue in fact that there are considerable uncertainties in the integrated properties of even the Milky Way clusters that are often overlooked.