1. South-Western Institute for Astronomy Research, Yunnan University , Kunming 650500, China
2. Department of Physics , University of Helsinki, Gustaf Hällströmin katu 2, FI-00014, Finland
3. Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS) , Daejeon 34126, Korea
4. Shanghai Astronomical Observatory, Chinese Academy of Sciences , Shanghai 200030, China
5. Department of Physics and Astronomy, University of Southern California , Los Angeles, CA 90089, USA