Obscured Growth in the age of Roman and Massively Multiplexed Spectroscopic Facilities

Most bulge-dominated galaxies host black holes with masses that tightly correlate with the masses of their bulges. This may indicate that the black holes may regulate galaxy growth or vice versa or grow in lockstep. The quest to understand how, when, and where those black holes formed motivates much of extragalactic astronomy. Here we focus on a population of galaxies with active black holes in their nuclei (active galactic nuclei or AGN) that are fully or partially hidden by dust and gas: the emission from the broad-line region is either completely or partially obscured with a visual extinction of 1 or above. Though not yet precise, this limit appears to be the point at which the populations of AGN may evolve differently. Several X-ray through Radio imaging missions are geared to detect on the order of 10^5 obscured AGN. To realize the full scientific potential of these surveys, we must examine those objects using spectroscopic techniques to study their reddening properties, star-formation histories, and excitation conditions. With Roman's WFI-grism and massively multiplexed ground facilities we can efficiently measure ionized and hot molecular gas emission lines, probing star formation, AGN feedback, and gas flows in and between galaxies and the circum-galactic medium. Machine learning algorithms have immense potential at all stages of such work, from achieving superior sky subtraction for NIR ground spectra to classifying host morphologies in querying simulations. These key studies will shed light on the role of black holes in galaxy evolution during the epoch of peak growth activity.