Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 Quasars and Luminous Galaxies at 5.7 < z < 6.8

Abstract

We present spectroscopic identification of 32 new quasars and luminous galaxies discovered at 5.7 < z < 6.8. This is the second in a series of papers presenting the results of 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 photometric candidates were selected by a Bayesian probabilistic algorithm, and then observed with spectrographs on the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous paper, we have now identified 64 HSC sources over about 430 deg2, which include 33 high-z quasars, 14 high-z luminous galaxies, 2 [O III] emitters at z ~ 0.8, and 15 Galactic brown dwarfs. The new quasars have considerably lower luminosity (M1450 ~ -25 to -22 mag) than most of the previously known high-z quasars. Several of these quasars have luminous (> 10^(43) erg/s) and narrow (< 500 km/s) Ly alpha lines, and also a possible mini broad absorption line system of N V 1240 in the composite spectrum, which clearly separate them from typical quasars. On the other hand, the high-z galaxies have extremely high luminosity (M1450 ~ -24 to -22 mag) compared to other galaxies found at similar redshift. With the discovery of these new classes of objects, we are opening up new parameter spaces in the high-z Universe. Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ~ 6, are ongoing.

Accepted for publication in PASJ (HSC special issue); minor revisions made since ver. 1 and 2

References in corpus (28)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• A luminous quasar at a redshift of z = 7.085
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• The Hyper Suprime-Cam SSP Survey: Overview and Survey Design
• Observational constraints on Cosmic Reionization
• An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
• First Data Release of the Hyper Suprime-Cam Subaru Strategic Program
• Weak Gravitational Lensing with COSMOS: Galaxy Selection and Shape Measurements
• The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
• Super-Critical Growth of Massive Black Holes from Stellar-Mass Seeds
• Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV Luminosity Functions at $z\sim 4-7$ Derived with the Half-Million Dropouts on the 100 deg${}^2$ Sky
• A Survey of z~6 Quasars in the SDSS Deep Stripe: I. a Flux-Limited Sample at z_{AB}<21
• An optically-selected cluster catalog at redshift 0.1<z<1.1 from the Hyper Suprime-Cam Subaru Strategic Program S16A data
• The identification of z-dropouts in Pan-STARRS1: three quasars at 6.5<z<6.7
• Initial mass function of intermediate mass black hole seeds
• SILVERRUSH. III. Deep Optical and Near-Infrared Spectroscopy for Lya and UV-Nebular Lines of Bright Lya Emitters at z=6-7
• Discovery of eight z ~ 6 quasars from Pan-STARRS1
• Eight new luminous z > 6 quasars selected via SED model fitting of VISTA, WISE and Dark Energy Survey Year 1 Observations
• Six more quasars at redshift 6 discovered by the Canada-France High-z Quasar Survey
• The Subaru high-z quasar survey: discovery of faint z~6 quasars
• A population of high-redshift type-2 quasars-I. Selection Criteria and Optical Spectra
• First Discoveries of z>6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey
• Two bright z > 6 quasars from VST ATLAS and a new method of optical plus mid-infra-red colour selection
• Discovery of Eight z ~ 6 Quasars in the Sloan Digital Sky Survey Overlap Regions
• Discovering extremely compact and metal-poor, star-forming dwarf galaxies out to z ~ 0.9 in the VIMOS Ultra-Deep Survey
• Photometric brown-dwarf classification. I. A method to identify and accurately classify large samples of brown dwarfs without spectroscopy

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