Formation of massive Population III galaxies through photoionization feedback: a possible explanation for CR 7
Monthly Notices of the Royal Astronomical Society: Letters
We explore the formation of massive high-redshift Population III (Pop III) galaxies through photoionization feedback. We consider dark matter halos formed from progenitors that have undergone no star formation as a result of early reionization and photoevaporation caused by a nearby galaxy. Once such a halo reaches ≈ 10^9 M_, corresponding to the Jeans mass of the photoheated intergalactic medium (IGM) at z≈ 7, pristine gas is able to collapse into the halo, potentially producing a massive Pop
... II starburst. We suggest that this scenario may explain the recent observation of strong He II 1640 Å line emission in CR7, which is consistent with ∼ 10^7 M_ of young Pop III stars. Such a large mass of Pop III stars is unlikely without the photoionization feedback scenario, because star formation is expected to inject metals into halos above the atomic cooling threshold (∼ 10^8 M_ at z ≈ 7). We use merger trees to analytically estimate the abundance of observable Pop III galaxies formed through this channel, and find a number density of ≈ 10^-7 Mpc^-3 at z=6.6 (the redshift of CR7). This is approximately a factor of ten lower than the density of Lyα emitters as bright as CR7.