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Studies of the high-redshift rest-frame ultraviolet (UV) luminosity functions(LFs) have typically treated the star-forming galaxy and active galactic nuclei(AGN) populations separately, as they have different survey depth and arearequirements. However, the recent advent of wide-area deep ground-based imagingsurveys now probe volumes large enough to discover AGNs, at depths sensitiveenough for fainter star-forming galaxies, bridging these two populations. Usingresults from such surveys as observational constraints, we present amethodology to jointly empirically model the evolution of the rest-UVluminosity functions at z=3-9. We assume both populations have a LFwell-described by a double power law modified to allow a flattening at thefaint-end, and that all LF parameters evolve smoothly with redshift. Thisprovides a good fit to the observations, and makes predictions to volumedensities and redshifts not yet observed. We find that the volume density ofbright (M_UV = -28) AGNs rises by five orders of magnitude from z=9 to z=3,while modestly bright (M_UV = -21) galaxies rise by only two orders ofmagnitude across the same epoch. The observed bright-end flattening of the z=9LF is unlikely to be due to AGN, and rather is due to a shallowing of thebright-end slope, implying reduced feedback in bright galaxies at early times.Integrating our LFs we find that the intrinsic ionizing emissivity is dominatedby galaxies at all z > 3, and this result holds even after applying a notionalescape fraction. We compare our AGN LFs to predictions based on differentblack-hole seeding models, finding decent agreement on average, but that allmodels are unable to predict the observed abundance of bright AGNs. We makepredictions for the upcoming Euclid and Roman observatories, showing that theirrespective wide-area surveys should be capable of discovering AGNs to z ~ 8.

On the Co-Evolution of the AGN and Star-Forming Galaxy Ultraviolet Luminosity Functions at 3 < z < 9