Spectroscopy of Reionization-Era Analogs at z ~ 1 - 3: Implications for Early Star Forming Sources

The reionization of intergalactic hydrogen contains important clues to the history of cosmic structure formation. Galaxies in the reionization-era are found to present prominent rest-frame optical emission lines, as expected for galaxies experiencing rapidly rising star formation histories. Our knowledge of the physical properties of this population is limited, making it challenging to understand the role of star forming galaxies played in reionization and interpret the spectra emerging at z > 6. To address this shortcoming, I have conducted a large spectroscopic survey targeting rest-frame UV and optical emission lines in extreme [OIII] emitting galaxies at z ~ 1 - 3. In this thesis, I present four projects, constraining the nature of early star forming galaxies by studying the spectral properties of reionization-era analogs. First, I present the results identifying rest-frame optical emission lines in 227 extreme [OIII] emitters. By quantifying the ionizing production efficiency and [OIII]/[OII] ratio, I find that the most extreme [OIII] emitters are the most effective ionizing agents. Second, I present the results identifying rest-frame UV emission lines in extreme [OIII] emitters. I show that the intense CIII] and CIV emission seen at z > 6 are not entirely driven by a shift toward larger [OIII] EW, but may also be driven by a shift toward lower metallicities at earlier times. Third, using the Lyman-alpha EWs measured for extreme [OIII] emitters, I discuss the implications for Lyman-alpha visibility at z > 7 and the contribution of extreme [OIII] emitters to reionization. Fourth, I explore potential hidden older stellar population and gas properties of the most extreme [OIII] emitters. Finally, I conclude my thesis by exploring the upcoming spectroscopic studies of reionization-era galaxies with JWST. My results of reionization-era analogs at z ~ 1 - 3 will provide an empirical baseline for comparison with future z > 6 results