Outer space for untwisted automorphisms of right-angled Artin groups

For a right-angled Artin group A(Gamma), the untwisted outer automorphism group U(A(Gamma)) is the subgroup of Out. (A(Gamma)) generated by all of the Laurence-Servatius generators except twists (where a twist is an automorphism of the form v bar right arrow vw with vw = wv). We define a space Sigma(Gamma) on which U(A(Gamma)) acts properly and prove that Sigma(Gamma) is contractible, providing a geometric model for U(A(Gamma)) and its subgroups. We also propose a geometric model for all of Out. (A(Gamma)), defined by allowing more general markings and metrics on points of Sigma(Gamma)