Abstract
Abstract We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 [O iii] emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg2, surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Lyα emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ1240 emission and resembles that of lower-z narrow-line quasars, the small Lyα width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.
Highlights
Quasars in the high-z universe25 have been used as an unique probe into early cosmic history
The progress of cosmic reionization can be measured from H I absorption imprinted on the rest-frame ultraviolet (UV) spectrum of a high-z quasar; this absorption is very sensitive to the neutral fraction of the foreground intergalactic medium (IGM; Gunn & Peterson 1965; Fan et al 2006)
With this luminosity function (LF) shape, we predict that quasars are responsible for less than 10% of the ionizing photons that are necessary to keep the IGM fully ionized at z = 6
Summary
Quasars in the high-z universe have been used as an unique probe into early cosmic history. Matsuoka et al (2016, 2018a, 2018b, 2019) have already reported the discovery of 65 high-z quasars, along with 24 high-z luminous galaxies, 6 [O III] emitters at z ∼ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects include many low-luminosity quasars with redshifts up to z = 7.07, objects that have been difficult to find in past shallower surveys. We refer to z-band magnitudes with the AB subscript (“zAB”), while redshift z appears without a subscript
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