Automorphic realization of residual Galois representations

We show that it is possible in rather general situations to obtain a finite-dimensional modular representation p of the Galois group of a number field F as a constituent of one of the modular Galois representations attached to automorphic representations of a general linear group over F, provided one works "potentially." The proof is based on a close study of the monodromy of the Dwork family of Calabi-Yau hypersurfaces; this in turn makes use of properties of rigid local systems and the classification of irreducible subgroups of finite classical groups with certain sorts of generators.