Stuart Wyithe (Melbourne University)

Suppression of Dwarf Galaxy Formation by Cosmic Reionization - Stuart Wyithe colloquium

ATNF Marsfield Lecture Theatre

Abstract

Observations of the highest redshift quasars suggest that hydrogen in the inter-galactic medium was reionized at a redshift prior to z=6. Following reionization, fluctuations in the distribution of galaxies contributed to a scatter in the ionizing background, and hence in the ionization fraction of cosmic hydrogen on scales of tens of Mpc, as observed along the lines of sight to the earliest known quasars. Theoretical simulations predict that the formation of dwarf galaxies should have been suppressed after cosmic hydrogen was reionized, leading to a drop in the cosmic star formation rate. In this talk I present evidence for this suppression. I will show that the post-reionization galaxies which produced most of the ionizing radiation at a redshift z~5.5, must have had a mass in excess of ~1010 solar masses or else the aforementioned scatter would have been smaller than observed. This limiting mass is two orders of magnitude larger than the galaxy mass that is thought to have dominated the reionization of cosmic hydrogen.