Eigenfunction expansions of ultradifferentiable functions and ultradistributions

In this paper we give a global characterisation of classes of ultradifferentiable functions and corresponding ultradistributions on a compact manifold X X . The characterisation is given in terms of the eigenfunction expansion of an elliptic operator on X X . This extends the result for analytic functions on compact manifolds by Seeley in 1969, and the characterisation of Gevrey functions and Gevrey ultradistributions on compact Lie groups and homogeneous spaces by the authors (2014).