1. CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
2. School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China
3. Department of Physics, University of Connecticut, Storrs, CT 06269, USA
4. Department of Astronomy, Xiamen University, Xiamen, Fujian 361005, China