Metal-free galaxy candidates discovered in CLASH

The first metals in the universe are expected to form in population III stars - primordial stars consisting entirely of hydrogen and helium. However, these stars have so far remained elusive. Simulations indicate that galaxies consisting exclusively, or almost exclusively, of population III stars may form at z>6, and such galaxies may provide one of the best probes of the properties of the population III star formation mode. By fitting Yggdrasil model spectra to multiband photometry data, we have identified four population III galaxy candidates in the Cluster Lensing and Supernova survey with Hubble (CLASH). We rule out alternative mundane galaxies and low redshift interlopers through similar fits to catalogs of spectra from more mundane objects. If confirmed through spectroscopy, this would constitute the first detection of the "missing link" between the early pristine universe and the metal-enriched universe.