Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 7.0

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 deg 2 , surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Ly α emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ 1240 emission and resembles that of lower- z narrow-line quasars, the small Ly α width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.