Doctor of Philosophy
Dr. Pauline Barmby
Dr. Sarah C. Gallagher
X-ray observations provide a unique perspective on the most energetic processes in the Universe. In particular, Low-mass X-ray binaries (LMXBs) found in globular clusters have been shown to depend on the mass, radius, and metallicity of the cluster. This thesis focuses on the impact environmental parameters have on X-ray sources and the underlying physical explanations for them.
I studied the X-ray binary population in M31 using 1 Ms of Chandra ACIS data and 6-filter photometry from the Panchromatic Hubble Andromeda Treasury Survey. From a sample of 83 star clusters we found the brightest and most compact star clusters preferentially hosted an X-ray source. %A logistic regression analysis showed that the F475W magnitude had the strongest correlation followed by the effective radius, while the (F475W-F814W) colour, a probe of metallicity, was not statistically significant. An investigation of 1566 HII regions found that neither radius nor H-alpha luminosity was a predictor of an HII region hosting an X-ray source.
I produced the most sensitive Chandra X-ray point source catalogue of M31, detecting \num\ X-ray sources in an area of ~0.6 degrees squared to a limiting unabsorbed 0.5-8.0 keV luminosity of 10E34 erg/s. The flatter completeness-corrected X-ray luminosity function of the bulge compared to the disk, consistent with previous work, indicated a lack of bright high-mass X-ray binaries in the disk and an aging population of LMXBs in the bulge. I also investigated the origin of the relationship between the metallicity of 109 Galactic globular clusters and LMXB formation by studying the number density of red giant branch (RGB) stars. Spearman and Kendall Rank tests between the RGB star density and metallicity [Fe/H] confirmed the data could not have been drawn from a random distribution.
Vulic, Neven, "X-ray Populations in The Local Group: Insights with Hubble & Chandra" (2016). Electronic Thesis and Dissertation Repository. 3802.