Caract\`eres automorphes d'un groupe r\'eductif

Let $G$ be a reductive group defined over a number field. Denote $Z(\widehat{G})$ the center of the dual group. Langlands has defined some homomorphism from some cohomology group of $Z(\widehat{G})$ into the group of automorphic characters of $G$. We prove that it is bijective.