The Infrared Medium-deep Survey. VI. Discovery of Faint Quasars at $z\sim5$ with a Medium-band-based Approach

• Main Authors: Kim, Yongjung, Im, Myungshin, Jeon, Yiseul, Kim, Minjin, Pak, Soojong, Taak, Yoon Chan, Choi, Changsu, Hong, Jueun, Hyun, Minhee, Ji, Tae-Geun, Jun, Hyunsung David, Karouzos, Marios, Kim, Dohyeong, Kim, Duho, Kim, Jae-Woo, Kim, Ji Hoon, Lee, Hye-In, Lee, Seong-Kook, Park, Won-Kee, Yoon, Yongmin, Byeon, Seoyeon, Hwang, Sungyong, Kim, Joonho, Kim, Sophia, Lim, Gu, Paek, Insu, Park, Woojin, Shin, Suhyun
• Format: Journal Article
• Language: English
• Published: 21-11-2018
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.1811.08606

The faint quasars with $M_{1450}>-24$ mag are known to hold the key to the
determination of the ultraviolet emissivity for the cosmic re-ionization. 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 $z\sim5$ faint quasar survey
with the Infrared Medium-deep Survey (IMS), which covers $\sim100$ deg$^{2}$
areas in $J$-band to the depths of $J_{\rm AB}\sim23$ 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 $z\sim5$,
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 quasars selection. We derived photometric redshifts from the
medium-band data, and find that they have high accuracies of $\langle|\Delta
z|/(1+z)\rangle=0.016$. The medium-band-based approach allows us to rule out
many of the interlopers that contaminate $\gtrsim20~\%$ of the
broad-band-selected quasar candidates. These results suggest that the
medium-band-based approach is a powerful way to identify $z\sim5$ 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 re-ionization
history.