The Infrared Medium-deep Survey. IX. Discovery of Two New $zsim6$ Quasars and Space Density down to $M_{1450}sim-23.5$ mag

Kavli Affiliate: Linhua Jiang

| First 5 Authors: Yongjung Kim, Myungshin Im, Yiseul Jeon, Minjin Kim, Linhua Jiang

| Summary:

We present the result of the Infrared Medium-deep Survey (IMS) $zsim6$
quasar survey, using the combination of the IMS near-infrared images and the
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) optical images. The
traditional color-selection method results in 25 quasar candidates over $86$
deg$^{2}$. We introduce the corrected Akaike Information Criterion (AICc) with
the high-redshift quasar and late-type star models to prioritize the candidates
efficiently. Among the color-selected candidates, seven plausible candidates
finally passed the AICc selection of which three are known quasars at $zsim6$.
The follow-up spectroscopic observations for the remaining four candidates were
carried out, and we confirmed that two out of four are $zsim6$ quasars. With
this complete sample, we revisited the quasar space density at $zsim6$ down to
$M_{1450}sim-23.5$ mag. Our result supports the low quasar space density at
the luminosity where the quasar’s ultraviolet ionizing emissivity peaks,
favoring a minor contribution of quasars to the cosmic reionization.

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