Clues to Globular Cluster Evolution from Multiwavelength Observations of Extragalactic Systems

TL;DR

This study investigates globular cluster systems in nearby galaxies across multiple wavelengths, revealing a strong link between low mass X-ray binaries and cluster metallicity, and highlighting potential observational biases affecting previous correlations.

Contribution

It provides new evidence of metallicity's role in LMXB presence within GCs and discusses the importance of accounting for systematic errors in color distribution analyses.

Findings

LMXBs are present in about half of the GCs.

Metal-rich GCs host three times more LMXBs than metal-poor ones.

Potential observational biases may affect previously reported GC correlations.

Abstract

We present a study of the globular cluster (GC) systems of nearby elliptical and S0 galaxies at a variety of wavelengths from the X-ray to the infrared. Our analysis shows that roughly half of the low mass X-ray binaries (LMXBs), that are the luminous tracers of accreting neutron star or black hole systems, are in clusters. There is a surprisingly strong correlation between the LMXB frequency and the metallicity of the GCs, with metal-rich GCs hosting three times as many LMXBs as metal-poor ones, and no convincing evidence of a correlation with GC age so far. In some of the galaxies the LMXB formation rate varies with GC color even within the red peak of the typical bimodal cluster color distribution, providing some of the strongest evidence to date that there are metallicity variations within the metal-rich GC peak as is expected in a hierarchical galaxy formation scenario. We also note that any analysis of subtler variations in GC color distributions must carefully account for both statistical and systematic errors. We caution that some published GC correlations, such as the apparent 'blue-tilt' or mass-metallicity effect might not have a physical origin and may be caused by systematic observational biases.