Probing the fluctuating ultraviolet background using the Hubble Frontier Fields

Abstract

In recent years, the rise in the number of Lyman Break Galaxies detected at high redshifts z ≥ 6 has opened up the possibility of understanding early galaxy formation physics in great detail. In particular, the faint-end slope (α) of the ultraviolet luminosity function (UV LF) of these galaxies is a potential probe of feedback effects that suppress star formation in low-mass haloes. In this work, we propose a proof-of-concept calculation for constraining the fluctuating UV background during reionization by constraining α in different volumes of the Universe. Because of patchy reionization, different volumes will experience different amount of photoheating which should lead to a scatter in the measured α. Our approach is based on a simple model of the UV LF that is a scaled version of the halo mass function combined with an exponential suppression in the galaxy luminosity at the faint end because of UV feedback. Although current data are not sufficient to constrain α in different fields, we expect that, in the near future, observations of the six-lensed Hubble Frontier Fields with the James Webb Space Telescope will offer an ideal test of our concept.