  Ultra-high-energy cosmic rays, accelerated hadrons that can exceed energies
of $10^{20}$ eV, are the highest-energy particles ever observed. While the
sources producing UHECRs are still unknown, the Pierre Auger Observatory has
detected a large-scale dipole anisotropy in the arrival directions of cosmic
rays above 8 EeV. In this work, we explore whether resolved gamma-ray sources
can reproduce the Auger dipole. We use various Fermi Large Area Telescope
catalogs as sources of cosmic rays in CRPropa simulations. We find that in all
cases, the simulated dipole has an amplitude significantly larger than that
measured by Auger, even when considering large extragalactic magnetic field
strengths and optimistic source weighting schemes. Our result implies that the
resolved gamma-ray sources are insufficient to account for the population of
sources producing the highest-energy cosmic rays, and there must exist a
population of UHECR sources that lack gamma-ray emission or are unresolved by
the current-generation gamma-ray telescopes.
