E. Zackrisson, A. Zitrin, M. Trenti, C. -E. Rydberg, L. Guaita, D. Schaerer, T. Broadhurst, G. Ostlin, T. Strom
Small galaxies consisting entirely of population III (pop III) stars may form at high redshifts, and could constitute one of the best probes of such stars. Here, we explore the prospects of detecting gravitationally lensed pop III galaxies behind the galaxy cluster J0717.5+3745 (J0717) with both the Hubble Space Telescope (HST) and the upcoming James Webb Space Telescope (JWST). By projecting simulated catalogs of pop III galaxies at z~7-15 through the cluster magnification maps, we estimate the lensed number counts as a function of flux detection threshold. We find that the ongoing HST survey CLASH, targeting a total of 25 galaxy clusters including J0717, potentially could detect a small number of pop III galaxies with intrinsic luminosities a factor of ~5 lower than those detectable in the deepest current HST images of unlensed fields. The situation for JWST is similar - relatively short JWST exposures of J0717 should be able to detect population III galaxies with intrinsic luminosities a factor of a few lower than those detectable even in ultra-deep JWST observations of unlensed fields, and in just a fraction of the exposure time spent on the latter. Galaxies in which as little at ~1e-3 of the baryons within the host halo have turned into pop III stars can in principle be detected this way. We also argue that the galaxy luminosity function at z=7-10 can be used to place upper limits on the typical star formation efficiencies of pop III galaxies, and present the constraints derived from current luminosity function measurements.
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http://arxiv.org/abs/1204.0517
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