1. Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany.
2. Department of Astronomy, School of Science, University of Tokyo, Bunkyoku, Tokyo 113-0033, Japan.
3. Research Center for the Early Universe, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
4. Istituto Nazionale di Astrofisica–Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste, Italy.
5. Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA.