A search for Population III galaxies in CLASH. I. Singly-imaged
  candidates at high redshift
  Population III galaxies are predicted to exist at high redshifts and may be
rendered sufficiently bright for detection with current telescopes when
gravitationally lensed by a foreground galaxy cluster. Population III galaxies
that exhibit strong Lya emission should furthermore be identifiable from
broadband photometry because of their unusual colors. Here, we report on a
search for such objects at z > 6 in the imaging data from the Cluster Lensing
And Supernova survey with Hubble (CLASH), covering 25 galaxy clusters in 16
filters. Our selection algorithm returns five singly-imaged candidates with
Lya-like color signatures, for which ground-based spectroscopy with current
8-10 m class telescopes should be able to test the predicted strength of the
Lya line. None of these five objects have been included in previous CLASH
compilations of high-redshift galaxy candidates. However, when large grids of
spectral synthesis models are applied to the study of these objects, we find
that only two of these candidates are significantly better fitted by Population
III models than by more mundane, low-metallicity stellar populations.
