A Fredholm determinant identity and the convergence of moments for random Young tableaux

We obtain an identity between Fredholm determinants of two kinds of operato rs, one acting on functions on the unit circle and the other acting on func tions on a subset of the integers. This identity is a generalization of an identity between a Toeplitz determinant and a Fredholm determinant that has appeared in the random permutation context. Using this identity, we prove, in particular, convergence of moments for arbitrary rows of a random Young diagram under Plancherel measure.