Ultra-faint high-redshift galaxies in the Frontier Fields

Abstract

By combining cosmological simulations with Frontier Field (FF) project lens models, we find that, in the most optimistic case, galaxies as faint as m ≈ 33-34 (AB magnitude at 1.6 μm) can be detected in the Frontier Fields. Such faint galaxies are hosted by dark matter haloes of mass ~10⁹ M_⊙ and dominate the ionizing photon budget over currently observed bright galaxies, thus allowing for the first time the investigation of the dominant reionization sources. In addition, the observed number of these galaxies can be used to constrain the role of feedback in suppressing star formation in small haloes: for example, if galaxy formation is suppressed in haloes with circular velocity v_c < 50 km s^-1, galaxies fainter than m = 31 should not be detected in the FFs.