Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). IX. Identification of two red quasars at z > 5.6

Nanako KATO, Yoshiki MATSUOKA, Masafusa ONOUE, Shuhei KOYAMA, Yoshiki TOBA, Masayuki AKIYAMA, Seiji FUJIMOTO, Masatoshi IMANISHI, Kazushi IWASAWA, Takuma IZUMI, Nobunari KASHIKAWA, Toshihiro KAWAGUCHI, Chien Hsiu LEE, Takeo MINEZAKI, Tohru NAGAO, Akatoki NOBORIGUCHI, Michael A. STRAUSS

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


We present the first discovery of dust-reddened quasars (red quasars) in the high-z universe (z > 5.6). This is a result from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which is based on the sensitive multi-band optical imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We identified four red quasar candidates from the 93 spectroscopically confirmed high-z quasars in the SHELLQs sample, based on detections in the Wide-field Infrared Survey Explorer (WISE) data at 3.4 and 4.6μm (rest-frame ∼5000-6500A° ). The amount of dust reddeningwas estimated with spectral energy distribution (SED) fits over optical andmidinfrared wavelengths. Two of the four candidates were found to be red quasars with dust reddening of E(B -V) > 0.1. The remaining SHELLQs quasars without individual WISE detections are significantly fainter in the WISE bands and bluer than the red quasars, although we did detect them in the W1 band in a stacked image. We also conducted the same SED fits for high-z optically-luminous quasars, but no red quasar was found. This demonstrates the power of Subaru HSC to discover high-z red quasars, which are fainter than the limiting magnitudes of past surveys in the rest-frame ultraviolet, due to dust extinction.

Original languageEnglish (US)
JournalPublications of the Astronomical Society of Japan
Issue number5
StatePublished - Oct 1 2020

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Early universe
  • Galaxies: High-redshift
  • Quasars: General


Dive into the research topics of 'Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). IX. Identification of two red quasars at z > 5.6'. Together they form a unique fingerprint.

Cite this