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Discovery of 16 new z ∼ 5.5 quasars: filling in the redshift gap of quasar color selection

Yang, Jinyi; Fan, Xiaohui; Wu, Xue-Bing; Wang, Feige; Bian, Fuyan; Yang, Qian; McGreer, Ian D.; Yi, Weimin; Jiang, Linhua; Green, Richard; Yue, Minghao; Wang, Shu; Li, Zefeng; Ding, Jiani; Dye, Simon; Lawrence, Andy

Discovery of 16 new z ∼ 5.5 quasars: filling in the redshift gap of quasar color selection Thumbnail


Jinyi Yang

Xiaohui Fan

Xue-Bing Wu

Feige Wang

Fuyan Bian

Qian Yang

Ian D. McGreer

Weimin Yi

Linhua Jiang

Richard Green

Minghao Yue

Shu Wang

Zefeng Li

Jiani Ding

Associate Professor

Andy Lawrence


We present initial results from the first systematic survey of luminous z ∼ 5.5 quasars. Quasars at z ∼ 5.5, the post-reionization epoch, are crucial tools to explore the evolution of intergalactic medium, quasar evolution, and the early super-massive black hole growth. However, it has been very challenging to select quasars at redshifts 5.3 ≤ z ≤ 5.7 using conventional color selections, due to their similar optical colors to late-type stars, especially M dwarfs, resulting in a glaring redshift gap in quasar redshift distributions. We develop a new selection technique for z ∼ 5.5 quasars based on optical, near-IR, and mid-IR photometric data from Sloan Digital Sky Survey (SDSS), UKIRT InfraRed Deep Sky Surveys—Large Area Survey (ULAS), VISTA Hemisphere Survey (VHS), and Wide Field Infrared Survey Explorer. From our pilot observations in the SDSS-ULAS/VHS area, we have discovered 15 new quasars at 5.3 ≤ z ≤ 5.7 and 6 new lower redshift quasars, with SDSS z band magnitude brighter than 20.5. Including other two z ∼ 5.5 quasars already published in our previous work, we now construct a uniform quasar sample at 5.3 ≤ z ≤ 5.7, with 17 quasars in a ∼4800 square degree survey area. For further application in a larger survey area, we apply our selection pipeline to do a test selection by using the new wide field J-band photometric data from a preliminary version of the UKIRT Hemisphere Survey (UHS). We successfully discover the first UHS selected z ∼ 5.5 quasar.


Yang, J., Fan, X., Wu, X., Wang, F., Bian, F., Yang, Q., …Lawrence, A. (2017). Discovery of 16 new z ∼ 5.5 quasars: filling in the redshift gap of quasar color selection. Astronomical Journal, 153(4), 184.

Journal Article Type Article
Acceptance Date Mar 6, 2017
Online Publication Date Mar 30, 2017
Publication Date Mar 30, 2017
Deposit Date Apr 27, 2017
Publicly Available Date Apr 27, 2017
Journal Astronomical Journal
Print ISSN 0004-6256
Electronic ISSN 1538-3881
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 153
Issue 4
Pages 184
Keywords Galaxies: active; Galaxies: high-redshift; Quasars: emission lines; Quasars: general
Public URL
Publisher URL
Additional Information Journal title: The Astronomical Journal; Article type: paper; Article title: Discovery of 16 Newz∼ 5.5 Quasars: Filling in the Redshift Gap of Quasar Color Selection; Copyright information: © 2017. The American Astronomical Society. All rights reserved.; Date received: 2016-10-23; Date accepted: 2017-03-06; Online publication date: 2017-03-30


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