1. Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich , Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
2. Astronomy Department, University of Washington , Seattle, WA 98195, USA
3. Department of Astronomy and Astrophysics, University of California , 1156 High Street, Santa Cruz, CA 95064, USA