Colloquium on Apr. 9, 2020

Exploring the tail end of reionization with Subaru/HSC

Speaker: Daichi Kashino (Department of Physics, ETH Zurich)

Venue: Video Conference

Time: 3:30 PM, Thursday, Apr. 9, 2020

Abstract: 

The connection between the IGM and galaxies at the end of cosmic reionization encodes information about the reionization process at earlier epochs.  A remarkable observational fact is that the Lya forest opacity is widely varying across quasar sightlines. Different possible scenarios accounting for the observed spatial variations in the HI optical depth predict different relations between the amount of residual neutral hydrogen and galaxy distribution.

To distinguish these models, we are carrying out galaxy surveys using Subaru/HSC at z~5-6 in the fields of z>6 bright quasars, whose Lyα forest spectra tell us about the neutral hydrogen structure along the sightlines. As the first remarkable result, we present evidence that a region of high effective Lyα optical depth at z~5.7 is associated with an underdensity of galaxies. This observation is consistent with scenarios in which large optical depth fluctuations arise due to fluctuations in the galaxy-dominant UV background, or due to residual neutral islands that are expected from reionization that ended at redshifts as low as z~5.5 or lower.