Dissertation: X-ray Populations in The Local Group: Insights with Hubble and Chandra

(Cassiopeia – Autumn/l’automne 2016)

neven vulic

by Neven Vulic
Thesis defended on June 21, 2016
University of Maryland, College Park
Thesis advisors: Dr. Pauline Barmby and Dr. Sarah C. Gallagher

Abstract
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. An investigation of 1566 H II regions found that neither radius nor H-alpha luminosity was a predictor of an H II region hosting an X-ray source. To study the faintest X-ray sources a stacking analysis of star clusters and H II regions was completed. Non-detections throughout resulted in upper limits of ~10×1032 erg/s. I produced the most sensitive Chandra X-ray point source catalogue of M31, detecting 795 X-ray sources in an area of ~0.6 deg2, to a limiting unabsorbed 0.5-8.0 keV luminosity of ~10×1034 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. A Spearman Rank test between the RGB star density and metallicity [Fe/H] confirmed the data could not have been drawn from a random distribution.

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