Quasars in a Neutral Universe: Chronicling the History of Reionization, Enrichment, and Black Hole Growth

ongoing

How the first luminous sources reionized diffuse baryons in the intergalactic medium (IGM) is one of the most fundamental open questions in cosmology. The latest CMB constraints suggest reionization occurred at z ~ 7-8, within the realm of the highest redshift quasars known. The overarching impetus of this proposal is that Euclid's imminent discovery of scores of bright quasar beacons in a neutral universe, combined with the exquisite sensitivity of JWST, will enable a set of qualitatively new absorption spectroscopy experiments. Abundant neutral hydrogen in the IGM imprints a distinct damping wing signature on quasar spectra, which we will exploit to obtain the best constraints on the timing of reionization to date. These same spectra provide a glimpse of baryonic structure prior to reionization, which we will use to determine whether X-rays emitted by primeval black holes during cosmic dawn pre-heated the IGM, and constrain the properties of the underlying dark matter. The quasar's own ionizing radiation powers a cosmological-scale HII region encoding its radiative history, which we propose to map in absorption to answer the enigmatic question of how supermassive black holes grew to 10^9 M_sun just 800 Myr after the Big Bang. The same massive stars which reionized the IGM inevitably exploded in supernovae polluting the Universe with metals. These metals, if they reside in the neutral IGM, manifest as a forest of low-ionization absorbers, which we will use to constrain early IGM enrichment, and trace the history and topology of reionization with cosmic time. By conducting end-to-end analyses encompassing observations, theoretical modeling, state-of-the-art simulations, and Bayesian inference, we will elevate the quantitative study of reionization to be on the same solid methodological and statistical footing as other precision cosmological measurements. The PI is uniquely positioned to achieve these goals and has a proven track record for this type of synergy.