Event

The recent observation of CR7 (Sobral et al. 2015), the brightest Lyman-alpha emitter at z~7, could be the first detection of Pop III stars (i.e. stars formed from primordial/extremely metal-poor gas). CR7 has strong He II 1640 angstrom line emission and no detected metal lines, as predicted for Pop III stars. However, the He II line luminosity corresponds to ~10^7 solar masses of Pop III stars, and such a large Pop III star cluster is generally be expected to be metal-enriched from previous star formation. I will discuss a formation channel for massive Pop III galaxies, based on photoionization feedback, which may explain how CR7 could consist of such a large mass of Pop III stars not yet polluted by metals.

Additionally, I will discuss constraints on the properties of Pop III stars that can be inferred from the cosmic microwave background optical depth measured by Planck.