Standard modules of affine Hecke algebras

Let $G$ be a connected reductive group defined and split over a non-archimedean local field $F$. We give a new geometric proof of a special case of a recent theorem of Solleveld. Namely, we show that the class of standard Iwahori-spherical $G(F)$-representations, a notion a priori dependent on the coefficient field being the complex numbers, is actually defined over $\overline{{\mathbb{Q}}_{\mathrm{\ell }}}$. An unpublished theorem of Clozel, proven with global techniques, says that the class of essentially square-integrable representations is also defined over $\overline{{\mathbb{Q}}_{\mathrm{\ell }}}$. As an application of our main result, we give a local proof of this theorem for inner forms of ${\mathrm{G}\mathrm{L}}_n$, as well as showing that standard representations of these groups are defined over $\overline{{\mathbb{Q}}_{\mathrm{\ell }}}$.