A Wide-Area View of Reionization and Massive Galaxy Formation

Abstract

Our understanding of the epoch of hydrogen reionization and galaxies present during the first billion years of cosmic history has advanced tremendously over the past two decades. Spectra of quasars and high-redshift galaxies reveal that reionization was well underway by z∼7 and was largely complete by z∼6 while extremely deep imaging surveys with the Hubble Space Telescope have delivered samples of nearly 1000 z≳7 galaxies. However, several questions remain regarding both the structure of reionization (i.e. the characteristics of large intergalatic HII regions formed during this process) as well as the physical properties z≳7 galaxies. In this dissertation, I focus on demonstrating how wide-area (≳square degree) datasets can help address these questions by probing scales relevant for the largest ionized bubbles, as well as providing large samples of luminous z≳7 galaxies that can be characterized in detail with existing facilities. Utilizing a large sample of UV-bright z≃7 galaxies identified over >2 square degrees, I find that such systems commonly exhibit strong rest-optical ([OIII]+Hβ) nebular line emission with a significant fraction likely highly efficient ionizing agents given their extreme optical line emission. I then present results from a large MMT/Binospec campaign, finding no strong evolution in the Lyman-alpha equivalent width distribution among UV-bright galaxies between z∼6−7, suggesting UV-bright z∼7 galaxies may often occupy large ionized bubbles. Subsequent ultra-deep Binospec follow up revealed a large-scale spectroscopic overdensity at z=6.8 likely associated with a very large (R ≳ 3 physical Mpc) ionized bubble. Combining the Binospec data with results from a large ALMA program, I find that extremely UV-luminous z≃7 galaxies commonly possess both large Lyα velocity offsets and line widths, helping explain how their Lyα emission is so easily visible through a partially neutral IGM. I then report the photometric identification and subsequent ALMA confirmation of a UV-bright z=6.853 galaxy harboring an extremely luminous highly-obscured radio-loud AGN as well as an intense dust-obscured starburst. Finally, I discuss how upcoming surveys can be used to better understand early supermassive black hole growth and the characteristics of the largest ionized bubbles formed during reionization.