Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope

TL;DR

This paper combines Planck and Hubble data to refine the timeline of cosmic reionization, showing that high-redshift star-forming galaxies likely drove the process, with implications for future astronomical observations.

Contribution

It provides a joint analysis of CMB and galaxy data to constrain reionization history, reducing the need for very early galaxies and supporting galaxy-driven reionization.

Findings

Reionization occurred mainly between redshifts 6 and 10.

Star-forming galaxies are the primary sources of reionization.

The optical depth tau is consistent with a reionization timeline within z~6 to 10.

Abstract

We discuss new constraints on the epoch of cosmic reionization and test the assumption that most of the ionizing photons responsible arose from high redshift star-forming galaxies. Good progress has been made in charting the end of reionization through spectroscopic studies of z~6-8 QSOs, gamma-ray bursts and galaxies expected to host Lyman-alpha emission. However, the most stringent constraints on its duration have come from the integrated optical depth, tau, of Thomson scattering to the cosmic microwave background. Using the latest data on the abundance and luminosity distribution of distant galaxies from Hubble Space Telescope imaging, we simultaneously match the reduced value tau=0.066 +/- 0.012 recently reported by the Planck collaboration and the evolving neutrality of the intergalactic medium with a reionization history within 6 <~ z <~ 10, thereby reducing the requirement for a significant population of very high redshift (z>>10) galaxies. Our analysis strengthens the conclusion that star-forming galaxies dominated the reionization process and has important implications for upcoming 21cm experiments and searches for early galaxies with James Webb Space Telescope.