Peking University April 25，2017: On April 12, the website AAS Nova highlighted recent research led by Yang Jinyi, PhD student at the Department of Astronomy, Peking University. His research article Discovery of 16 New z ~ 5.5 Quasars: Filling in the Redshift Gap of Quasar Color Selection was published earlier on March 30 by the Astronomical Journal (AJ).
Artist’s impression of a distant quasar [ESO]
A quasar is an active galactic nucleus of very high luminosity. It consists of a supermassive black hole surrounded by an orbiting accretion disk of gas and emits powerful energy. High redshift ( z > 5) quasars are important tracers to study the early universe. However, they are difficult to detect. One of the problems is contamination. Quasars at this distance are the same color in commonly used optical bands as cool M-dwarf stars. In order to avoid this contamination, surveys searching for quasars have often just cut out that entire section of the color space. Although more than 300,000 quasars are now known, only ~290 quasars are at z > 5. In the distribution of quasar redshift, there is an obvious gap of known quasars at 5.3 < z < 5.7, due to their similar optical colors to that of late-type stars. Only ~30 known quasars have been found in this redshift gap over a wide magnitude range.
The team, instructed by Professor Wu Xuebing and Professor Fan Xiaohui, has been working on exploring the gap caused by the same colors of z ~ 5.5 quasar and late-type stars in broad optical bands, they have recently developed a new selection technique for z ~ 5.5 quasars based on optical, near-IR, and mid-IR photometric data and built the first sample of quasars at 5.3 ≤ z ≤ 5.7. Using the new selection pipeline, the team has discovered a total of 21 new quasars from their main candidate sample, with 15 new quasars in the redshift range of 5.3 ≤ z ≤ 5.7, which nearly doubles the number of known quasars at z ~ 5.5. The selection function shows a high completeness at M1450< -26 , which can be expected to provide a sample of new z ~ 5.5 quasars for measurement of quasar luminosity function at this redshift gap and exploration of the evolution of intergalactic medium and early super-massive black hole growth.
The research was supported by National Natural Science Foundation of China (NNSF), Ministry of Science and Technology and Chinese Academy of Sciences.
Figure 2 (Left): Distribution of all previously known quasars and the newly discovered quasars[AJ]
Figure 2 (Right): Distribution of our newly discovered quasars[AJ]
The American Astronomical Society (AAS) is the major organization of professional astronomers in North America.
The Astronomical Journal (AJ) publishes original astronomical research, with an emphasis on significant scientific results derived from observations, including descriptions of data capture, surveys, analysis techniques and astronomical interpretation.
AAS Nova highlights results published in the AAS's peer-reviewed journals.
The European Southern Observatory (ESO) is the foremost intergovernmental astronomy organization in Europe
Written by: Li Xiaotong
Edited by: Wang Yuqing／Gan Zhonghao