Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level





Bret D. Lehmer

Committee Member

Julia Kennefick

Second Committee Member

Daniel Kennefick

Third Committee Member

Pradeep Kumar


accretion states, extragalactic astronomy, luminous infrared galaxies, ultraluminous X-ray sources, X-ray binaries


X-ray binary systems (XRBs) consist of a compact object component (e.g., black hole or neutron star) that accretes matter from a companion star. Although the extent to which XRBs contributed to the early heating of the intergalactic medium is still under investigation, it is estimated that XRBs dominated the X-ray radiation field before the reionization epoch. The study of XRB emission is therefore crucial to our understanding of the very early universe. Furthermore, studying the abundance and radial distribution of each XRB type within a galaxy can be revealing of the host galaxy’s local properties, structure, and evolution. XRB spectra can also be probed to understand the black holes (BHs) and neutron stars (NSs) they contain, which are often progenitors to more complex objects of astrophysical interest (e.g., gravitational-wave producing sources, millisecond pulsars, and short γ-ray bursts). Given their relationship to so many areas of astrophysics, XRB studies are vitally important to understanding the nature and history of the Universe. I utilize X-ray observations of nearby galaxies to study the nature, formation timescales, time evolution and accretion state demographics of XRB populations in various extragalactic environments.Chapter 1 investigates the nature of the ultraluminous X-ray source (ULX) M33 X-8. While unable to draw firm conclusions on the type of compact object (neutron star or black hole) in M33 X-8, we can rule out previously acceptable sub-Eddington accretion and pure advection-dominated disk models for X-8. Instead, we find the constraints are consistent with more recent models of super-Eddington accretion onto either a BH or NS. These results provide evidence for the existence of ULX systems undergoing super-Eddington accretion and will help to inform population synthesis models. Chapter 2 addresses recent observations of significant X-ray emission deficits from luminous infrared galaxies (LIRGs), the most extreme star-forming galaxies in the nearby Universe. Observations of NGC 7552, a relatively nearby LIRG with an X-ray emission ≈5 times lower than expected, provide key insight into the nature of X-ray emission in extreme star-forming environments. Our findings suggest the pairing of “bursty” star-formation histories with relatively young cluster ages predominantly drive the X-ray emission deficit in this galaxy. These results have broader implications for XRB formation timescales in LIRGs and other extreme star-forming environments. Chapter 3 presents a novel method for investigating XRB accretion state demographics in extragalactic environments. Recent innovative studies with the NuSTAR X-ray telescope have demonstrated the utility of hardness–intensity and hardness–hardness diagrams in differentiating between XRB accretion states in extragalactic environments. We show that XMM-Newton also has the ability to discriminate between XRB accretion states in other galaxies. We leverage the vast 22–year XMM-Newton archive of galaxy data, along with newly awarded XMM-Newton and NuSTAR data, to investigate XRB accretion behaviors in various environments.