The Pan-STARRS1 z>5.6 quasar survey II: Discovery of 55 Quasars at 5.6<z<6.5

TL;DR

This paper reports the discovery and spectroscopic confirmation of 55 quasars at redshifts 5.6 to 6.5 from Pan-STARRS1 and VIKING surveys, providing valuable data for understanding early universe structures and black holes.

Contribution

It presents a large, diverse sample of high-redshift quasars, including rare types, and offers the first measurement of the z~6 quasar luminosity function from Pan-STARRS1.

Findings

55 quasars confirmed at 5.6<z<6.5

Discovery of rare quasar types including blazar candidate and gravitational lens

First measurement of the z~6 quasar luminosity function

Abstract

The identification of bright quasars at z>6 enables detailed studies of supermassive black holes, massive galaxies, structure formation, and the state of the intergalactic medium within the first billion years after the Big Bang. We present the spectroscopic confirmation of 55 quasars at redshifts 5.6<z<6.5 and UV magnitudes -24.5<M1450<-28.5 identified in the optical Pan-STARRS1 and near-IR VIKING surveys (48 and 7, respectively). Five of these quasars have been independently discovered in other studies. The quasar sample shows an extensive range of physical properties, including 17 objects with weak emission lines, ten broad absorption line quasars, and five with strong radio emission (radio-loud quasars). There are also a few notable sources in the sample, including a blazar candidate at z=6.23, a likely gravitationally lensed quasar at z=6.41, and a z=5.84 quasar in the outskirts of the nearby (D~3 Mpc) spiral galaxy M81. The blazar candidate remains undetected in NOEMA observations of the [CII] and underlying emission, implying a star-formation rate <30-70 Msun/yr. A significant fraction of the quasars presented here lies at the foundation of the first measurement of the z~6 quasar luminosity function from Pan-STARRS1 (introduced in a companion paper). The quasars presented here will enable further studies of the high-redshift quasar population with current and future facilities.