Measuring the Reionization History with Quasar Damping Wings

The Lyman-alpha damping wing from neutral hydrogen in the intergalactic medium is predicted to be a key signature of the reionization epoch in the spectra of high-redshift quasars. There are substantial challenges in measuring and interpreting this signal, however: the intrinsic (i.e. unabsorbed) spectrum of the quasar near its Lyman-alpha line is unknown, and the impact of neutral gas on the spectrum depends on the large-scale structure of reionization, the small-scale distribution of baryons, and the age of the quasar. We have developed a Principal Component Analysis-based machine-learning approach to predict the intrinsic quasar spectrum, and have combined semi-numerical simulations of reionization with 1D radiative transfer through hydrodynamical simulations to predict the full range of proximity zone and damping wing morphologies. Using a Bayesian statistical formalism we can then translate an observed quasar spectrum into joint constraints on the neutral fraction and the quasar lifetime. I will demonstrate the application of these methods to the highest redshift quasars known, and discuss the potential for existing quasar spectra to constrain the reionization history between redshift 6 and 7 and the growth of the first supermassive black holes.

Speaker: Fred Davies, UC Santa Barbara