The Infrared Medium-deep Survey. VII. Faint Quasars at z ∼ 5 in the ELAIS-N1 Field

• Published in: The Astrophysical journal Vol. 893; no. 1; pp. 45 - 57
• Main Authors: Shin, Suhyun, Im, Myungshin, Kim, Yongjung, Hyun, Minhee, Pak, Soojong, Jeon, Yiseul, Ji, Tae-Geun, Ahn, Hojae, Byeon, Seoyeon, Han, Jimin, Hwang, Sungyong, Kim, Sophia, Lim, Gu, Paek, Insu, Paek, Gregory S. H., Taak, Yoon Chan, Choi, Changsu, Hong, Jueun, Jun, Hyunsung David, Kim, Dohyeong, Kim, Duho, Kim, Minjin, Kim, Jae-Woo, Kim, Ji Hoon, Lee, Hye-In, Lee, Seong-Kook, Park, Won-Kee, Park, Woojin, Yoon, Yongmin
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-04-2020; IOP Publishing
• Subjects: Active galactic nuclei; Active galaxies; Astrophysics; Broadband; Density; Early universe; Infrared Space Observatory (ISO); Intergalactic media; Ionization; Luminosity; Near infrared astronomy; Observational astronomy; Polls & surveys; Quasars; Reionization; Sky surveys; Spectral energy distribution
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab7bde

The intergalactic medium (IGM) at z ∼ 5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with , but their number density is poorly constrained at z ∼ 5. In this paper, we present our survey of faint quasars at z ∼ 5 in the European Large-Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg2 and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find z ∼ 5 quasars through a two-step approach using the broadband color selection, and spectral energy distribution fitting with the medium-band information included. Adopting Bayesian information criterion, we identify 10 promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at z ∼ 5 and supporting the reliability of the quasar selection. Using the promising candidates, we derive the z ∼ 5 quasar luminosity function at −26 M1450 −23. The number density of faint z ∼ 5 quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at z ∼ 5.