Upper limits on the mass and luminosity of Population III-dominated galaxies

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We here derive upper limits on the mass and luminosity of Population III (POPIII) dominated proto-galaxies based on the collapse of primordial gas under the effect of angular momentum loss via Lyα radiation drag and the gas accretion onto a galactic centre. Our model predicts that POPIII-dominated galaxies at z 7 are hosted by haloes with M halo 1.5 × 10⁸ - 1.1 × 10⁹ M, that they have Lyα luminosities of L Lyα 3.0 × 10⁴² - 2.1 × 10⁴³ erg/s, stellar mass of M star 0.8 × 10⁵ - 2.5 × 10⁶ M, and outflowing gas with velocities V out 40 km/s due to Lyα radiation pressure. We show that the POPIII galaxy candidate CR7 violates the derived limits on stellar mass and Lyα luminosity and thus is unlikely to be a POPIII galaxy. POPIII-dominated galaxies at z 7 have HeII line emission that is 1- 3 orders of magnitude lower then that of Lyα, they have high Lyα equivalent width of > 300 Å and should be found close to bright star forming galaxies. The HeII 1640 Å line is in comfortable reach of next generation telescopes, like the JWST or TMT.