Detecting gravitationally lensed population III galaxies with the Hubble Space Telescope and the James Webb Space Telescope

摘要

Small galaxies consisting entirely of population III (pop III) stars may format high redshifts, and could constitute one of the best probes of such stars.Here, we explore the prospects of detecting gravitationally lensed pop IIIgalaxies behind the galaxy cluster J0717.5+3745 (J0717) with both the HubbleSpace Telescope (HST) and the upcoming James Webb Space Telescope (JWST). Byprojecting simulated catalogs of pop III galaxies at z~7-15 through the J0717magnification maps, we estimate the lensed number counts as a function of fluxdetection threshold. We find that the ongoing HST survey CLASH, targeting atotal of 25 galaxy clusters including J0717, potentially could detect a smallnumber of pop III galaxies if ~1% of the baryons in these systems have beenconverted into pop III stars. Using JWST exposures of J0717, this limit can bepushed to ~0.1% of the baryons. Ultra-deep JWST observations of unlensed fieldsare predicted to do somewhat worse, but will be able to probe pop III galaxieswith luminosities intermediate between those detectable in HST/CLASH and inJWST observations of J0717. We also explain how current measurements of thegalaxy luminosity function at z=7-10 can be used to constrain pop III galaxymodels with very high star formation efficiencies (~10% of the baryonsconverted into pop III stars).