The Infrared Medium-deep Survey. VI. Discovery of Faint Quasars at z ∼ 5 with a Medium-band-based Approach

Yongjung Kim, Myungshin Im, Yiseul Jeon, Minjin Kim, Soojong Pak, Yoon Chan Taak, Changsu Choi, Jueun Hong, Minhee Hyun, Tae Geun Ji, Hyunsung David Jun, Marios Karouzos, Dohyeong Kim, Duho Kim, Jae Woo Kim, Ji Hoon Kim, Hye In Lee, Seong Kook Lee, Won Kee Park, Yongmin YoonSeoyeon Byeon, Sungyong Hwang, Joonho Kim, Sophia Kim, Gu Lim, Insu Paek, Woojin Park, Suhyun Shin

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21 Scopus citations

Abstract

The faint quasars with M 1450 > -24 mag are known to hold the key to the determination of the ultraviolet emissivity for the cosmic reionization. But only a few have been identified so far because of the limitations on the survey data. Here we present the first results of the z ∼ 5 faint quasar survey with the Infrared Medium-deep Survey (IMS), which covers ∼100 deg2 areas in J band to the depths of J AB ∼ 23 mag. To improve selection methods, the medium-band follow-up imaging has been carried out using the SED camera for QUasars in Early uNiverse (SQUEAN) on the Otto Struve 2.1 m Telescope. The optical spectra of the candidates were obtained with 8 m class telescopes. We newly discovered 10 quasars with -25 < M 1450 < -23 at z ∼ 5, among which three have been missed in a previous survey using the same optical data over the same area, implying the necessity for improvements in high-redshift faint quasar selection. We derived photometric redshifts from the medium-band data and found that they have high accuracies of . The medium-band-based approach allows us to rule out many of the interlopers that contaminate ≳20% of the broadband-selected quasar candidates. These results suggest that the medium-band-based approach is a powerful way to identify z ∼ 5 quasars and measure their redshifts at high accuracy (1%-2%). It is also a cost-effective way to understand the contribution of quasars to the cosmic reionization history.

Original languageEnglish
Article number86
JournalAstrophysical Journal
Volume870
Issue number2
DOIs
StatePublished - 10 Jan 2019

Keywords

  • cosmology: observations
  • galaxies: active
  • galaxies: high-redshift
  • quasars: supermassive black holes
  • surveys

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