Wednesday

Early star-forming galaxies at redshifts z>6 in the epoch of cosmic reionization are at the frontier of observability with the current instrumentation and represent the progenitors of present-day galaxies. The galaxy stellar mass function (GSMF) at z~6-9 is therefore a robust and crucial tool to study the build-up of stellar mass in the Universe and provides the tightest constraints on cosmological simulations. The observation of a decline in galaxy number density towards very low masses, i.e. a turnover at the very low-mass end of the GSMF, is of particular interest to constrain the evolution of the underlying dark matter halos in numerical simulations: The drop in number density of galaxies at high-redshifts provides strong constraints on the characteristic halo mass scale at which stellar feedback (supernovae and winds from massive stars) can suppress star formation.
I will present our recent work on the low-mass end of the GSMF at z=6-7 and the tentative detection of a downward turnover on the low-mass end using the gravitational magnification of the Hubble Frontier Fields clusters. I will then discuss these results regarding strong lensing and SED-fitting uncertainties in order to assess what is believable in the resulting mass function when considering these uncertainties.