Lower Redshift Analogues of the Sources of Reionization

TL;DR

This paper explores faint z~3 Lyman alpha emitters with extended emission regions as potential analogues to early universe sources of reionization, highlighting their properties that could facilitate ionizing photon escape.

Contribution

It identifies and discusses faint, interacting galaxies at z~3 as analogues to reionization sources, emphasizing their potential for higher ionizing photon escape fractions.

Findings

Faint z~3 Lyman alpha emitters show asymmetric, extended emission regions.

These galaxies exhibit features conducive to ionizing radiation escape.

Interactions and mergers at higher redshift may enhance reionization contributions.

Abstract

Known populations of QSOs appear to fall short of producing the ionizing flux required for re-ionizing the universe. The alternative, galaxies as sources of ionizing photons, suffers from the problem that known types of galaxies are almost completely opaque to ionizing photons. For reionization to happen, either large numbers of (largely undiscovered) sources are required, or the known populations of galaxies need to have had a much larger escape fraction for ionizing radiation in the past. We discuss recent discoveries of faint z~3 Lyman alpha emitters with asymmetric, extended Lyman alpha emission regions, which apparently are related to interacting galaxies. The unusually shaped line profiles and the underlying stellar populations of these objects suggest the presence of damaged gaseous halos, infall of gas, tidal or stripped stellar features and young populations of hot stars, that would all be conducive to the release of ionizing radiation. As galaxy interactions and mergers increase with redshift, these effects can only become more important at earlier times, and so these interacting z~3 objects may be late, lower redshift analogues of the sources of reionization.