Linhua Jiang, Ian D. McGreer, Xiaohui Fan, Fuyan Bian, Zheng Cai, Benjamin Clément, Ran Wang, Zhou Fan

Research output: Contribution to journalArticle

32 Scopus citations


We present the discovery of eight quasars at z ∼ 6 identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg2 (more than one-fourth of the total footprint). These overlap regions provide a unique data set that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i-band dropout objects in the SDSS imaging database. We then carried out a series of follow-up observations in the optical and near-IR to improve photometry, remove contaminants, and identify quasars. The eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude (|b| > 30°). These quasars span a redshift range of 5.86 < z < 6.06 and a flux range of 19.3 < zAB < 20.6 mag. Five of them are fainter than zAB = 20 mag, the typical magnitude limit of z ∼ 6 quasars used for the SDSS single-epoch images. In addition, we recover eight previously known quasars at z ∼ 6 that are located in the overlap regions. These results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and they provide guidance to a future systematic survey over all SDSS imaging regions with repeat observations.

Original languageEnglish (US)
Article number188
JournalAstronomical Journal
Issue number6
StatePublished - Jun 1 2015


  • cosmology: observations
  • quasars: emission lines
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Jiang, L., McGreer, I. D., Fan, X., Bian, F., Cai, Z., Clément, B., Wang, R., & Fan, Z. (2015). DISCOVERY OF EIGHT z ∼ 6 QUASARS IN THE SLOAN DIGITAL SKY SURVEY OVERLAP REGIONS. Astronomical Journal, 149(6), [188].