On the polar decomposition of right linear operators in quaternionic Hilbert spaces

In this article we prove the existence of the polar decomposition for densely defined closed right linear operators in quaternionic Hilbert spaces: If $T$ is a densely defined closed right linear operator in a quaternionic Hilbert space $H$, then there exists a partial isometry $U_0$ such that $T=U_0\mathrm{\mid }T\mathrm{\mid }$. In fact $U_0$ is unique if $N(U_0)=N(T)$. In particular, if $H$ is separable and $U$ is a partial isometry with $T=U\mathrm{\mid }T\mathrm{\mid }$, then we prove that $U=U_0$ if and only if either $N(T)=\{0\}$ or $R(T{)}^{\mathrm{\perp }}=\{0\}$.