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 similar to 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 Lya emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N V.1240 emission and resembles that of lower-z narrow-line quasars, the small Lya width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.