Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 $\le$ z $\le$ 7.0

TL;DR

This paper reports the discovery of 35 new high-redshift quasars and luminous galaxies using Subaru's Hyper Suprime-Cam, expanding the known sample and revealing diverse spectral features indicative of complex quasar-galaxy systems.

Contribution

It presents the tenth SHELLQs paper, adding 28 quasars and 7 galaxies at z=5.7-7.0, and discusses unique spectral properties of a subset with narrow Ly alpha emission.

Findings

Discovered 28 quasars and 7 luminous galaxies at z=5.7-7.0.

Identified a subset with narrow Ly alpha emission, possibly indicating quasar-star-forming galaxy composites.

Expanded the high-z quasar sample to 93 objects, enhancing understanding of early universe objects.

Abstract

We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 $\le$ z $\le$ 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 multi-band 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 Ly alpha 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 Ly alpha width may suggest a significant contribution from the host galaxies. Thus these objects may be composites of quasars and star-forming galaxies.