A multiwavelength analysis of M31's globular clusters and their low mass X-ray binaries

Abstract

A multiwavelength analysis of M31’s globular clusters and their low mass X-ray binaries by Mark B. Peacock Globular clusters (GCs) are dense groups of thousands to millions of stars. They are often very old systems with ages similar to those of their host galaxies and the early Universe. These clusters provide unique laboratories for astrophysical research and have been used by countless studies to improve our understanding of the Universe. In particular, they are ideal locations for studying stellar evolution and the formation and evolution of galaxies. They also provide unique locations for studying individual exotic objects, such as X-ray binaries. In this study, I investigate the properties of GCs in the nearby spiral galaxy, M31. This galaxy hosts the largest GC population in the Local Group. This, combined with its relative proximity to us, makes it an important bridge between studies of Galactic and extragalactic GCs. However, previous catalogues of these clusters have suffered from significant inhomogeneity and contamination from both stars and galaxies. In this contribution I present new, homogeneous, optical and near infra-red photometry of the M31 GC system. In addition to this, the structural parameters for over half of the known clusters are determined through fitting point spread function convolved King models to their density profiles. This photometry is used to remove significant contamination from non-cluster sources in previous cluster catalogues and to confirm a large population of young clusters in the M31 cluster system. Determining the properties of these clusters is very important in investigating both this, and other, GC systems. It is also of great benefit in investigating the exotic objects hosted by these clusters. I combine these data with archived XMM Newton observations, to study the low mass X-ray binaries (LMXBs) in M31’s clusters. LMXBs are known to be relatively common in GCs and, through studying the properties of the GCs which host them, it is possible to investigate the effects of cluster environment on the formation and evolution of these systems. From this work, I demonstrate that the presence of LMXBs is proportional to the stellar collision rate of a GC. This provides good observational evidence that these LMXBs are formed through dynamical interactions. These data are also used to consider the morphology of horizontal branch stars in M31’s GCs. Published GALEX ultraviolet observations of these clusters are used as a probe into their hot stellar populations. From this work, I propose a relationship between the core density of these clusters and their ultraviolet colour. This result suggests that the formation of (FUV bright) extreme horizontal branch stars may be enhanced in dense stellar environments through stellar interactions

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