Oral Presentation

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

Author(s): Suhyun Shin (SNU), Myungshin Im (SNU) and CEOU team

Presenter: SUHYUN Shin (Seoul National University)

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 -26 < M1450 < -23, 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/nearinfrared
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.