The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe

TL;DR

This paper presents a large sample of over 100 high-redshift quasars identified using the Pan-STARRS1 survey, significantly expanding the known population and enabling statistical studies of the early universe.

Contribution

It extends previous quasar selection methods to the Pan-STARRS1 survey, discovering 63 new quasars at z>5.6, nearly doubling the known sample at these redshifts.

Findings

Sample includes 124 quasars at 5.6<z<6.7 with diverse properties.

Composite spectra reveal variety in emission line features.

Sample spans a factor of ~20 in luminosity.

Abstract

Luminous quasars at z>5.6 can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far these studies have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare and therefore wide-field surveys are required to identify them and multiwavelength data are needed to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for z~6 quasars presented in Banados et al. (2014) using the Pan-STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range 5.6<z<6.7 that satisfy our selection criteria. Seventy-seven of these quasars have been discovered with PS1, and 63 of them are newly identified in this paper. We present composite spectra of the PS1 distant quasar sample. This sample spans a factor of ~20 in luminosity and shows a variety of emission line properties. The number of quasars at z>5.6 presented in this work almost double the quasars previously known at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.