Session B06: Cecilia Payne-Gaposchkin Thesis Prize

Live

Low mass galaxies have provided some of the best constraints we have on the nature of dark matter. In my thesis, I used innovative methods and instrumentation as well as original observations to discover such faint galaxies in the nearby universe and study their dark matter content. I characterized various aspects of the intriguing population of the so-called Ultra Diffuse Galaxies in group and cluster environments. Ultra Diffuse Galaxies hold the promise of new constraints on low mass galaxy dynamics, as their spatial extent and often significant globular cluster populations provide probes on spatial scales where dark matter should dominate the kinematics. Using Keck and Hubble Space Telescope observations, I provided the strongest evidence yet for the existence of a class of galaxies that lack dark matter. I also worked on the construction, software design, and operations of the Dragonfly Telescope which was designed to image large and extremely faint structures in the night sky. I designed and am leading the Dragonfly Wide Field Survey, a comprehensive survey of the low surface brightness Universe. This innovative and field-leading new survey provides unique constraints on the census and properties of dwarf galaxies beyond our local galactic neighborhood.   

Live

Models for black hole formation from stellar evolution robustly predict the existence of a pair-instability supernova mass gap in the range $\sim50$--$120\,M_\odot$. The binary black holes of LIGO-Virgo's first two observing runs supported this prediction, showing evidence for a dearth of component black hole masses above $45\,M_\odot$. Meanwhile, among the 30+ new observations from the third observing run, there are several black holes that appear to sit above the $45\,M_\odot$ limit. I will discuss how these unexpectedly massive black holes fit into our understanding of the binary black hole population. The data are consistent with several scenarios, including a mass distribution that evolves with redshift and the possibility that the most massive binary black hole, GW190521, straddles the mass gap, containing an intermediate-mass black hole with mass above $120\,M_\odot$.   

Live

Fast radio bursts (FRBs) are millisecond extragalactic radio transients of elusive origin that were first discovered in 2007. Some FRBs repeat and some apparently do not, even after hundreds of hours of follow-up observations. In order to unravel the origin of FRBs we have to detect a large population of them, ideally with one instrument. In my thesis, I have shown how to set up a real-time survey for FRBs with a novel telescope that does exactly that: the CHIME/FRB experiment. I have contributed significantly to the development of the hardware systems, the real-time and offline data pipelines. I show how to automatically associate events detected by CHIME/FRB with known sources of radio transients. We have detected 18 new repeating sources of FRBs and I characterize their burst morphologies, in order to understand better how they are emitted and how their signal has propagated through the interstellar medium. Finally, I show how to differentiate between one-off FRBs and repeating sources by way of their burst morphologies. I confirm that repeater bursts, on average, have larger widths and I show, for the first time, that repeater bursts, on average, are narrower in bandwidth.