Identifying the Reionization Redshift from the Cosmic Star Formation Rate

Abstract

We show that the cosmic star formation rate per comoving volume should exhibit a distinct drop around the reionization redshift, when the H II regions in the intergalactic medium around individual ionizing sources Ðrst overlapped. The drop results from the increase in the temperature of the inter-galactic medium as it was photoionized, and the consequent suppression of the formation of low-mass galaxies. We show quantitatively that the detection of this drop, which is marked by a corresponding fall in the number counts of faint galaxies, should become feasible over the coming decade with the Next Generation Space T elescope.