The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z\sim 5$ in the ELAIS-N1 Field

Abstract

The intergalactic medium (IGM) at $z\sim$ 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 $-26\lesssim M_{1450}\lesssim -23$, but their number density is poorly constrained at $z\sim 5$. In this paper, we present our survey of faint quasars at $z\sim 5$ in the European Large-Area {\it ISO} Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg${}^2$ 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 $z\sim 5$ quasars through a two-step approach using the broadband color selection, and SED fitting with the medium-band information included. Adopting Bayesian information criterion, we identify ten promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at $z\sim 5$ and supporting the reliability of the quasar selection. Using the promising candidates, we derive the $z\sim 5$ quasar luminosity function at $-26\lesssim M_{1450}\lesssim -23$. The number density of faint $z\sim 5$ 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 $z\sim 5$

16 pages, 9 figures, 4 tables. Accepted for publication in ApJ

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Cited by in corpus (13)

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• On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5
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• The rapid transition from star-formation to AGN dominated rest-frame UV light at z ~ 4
• Pure Density Evolution of the Ultraviolet Quasar Luminosity Function at $2\lesssim z\lesssim 6$
• Eddington Ratios of Dust-obscured Quasars at $z\lesssim 1$: Evidence Supporting Dust-obscured Quasars as Young Quasars
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• Candidate z ~ 2.5 Lyman Continuum Sources in the GOODS Fields
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• Medium-band observation of the neutrino emitting blazar, TXS 0506+056
• The quasar luminosity function at $z\sim 5$ via deep learning and Bayesian information criterion
• High-$z$ Universe probed via Lensing by QSOs (HULQ) II. Deep GMOS spectroscopy of a QSO lens candidate
• The impact of black hole feedback on the UV luminosity and stellar mass assembly of high-redshift galaxies