The Extremely Luminous Quasar Survey in the Sloan Digital Sky Survey Footprint. II. The North Galactic Cap Sample

Abstract

We present the North Galactic Cap sample of the Extremely Luminous Quasar Survey (ELQS-N), which targets quasars with M 1450 < −27 at 2.8 ≤ z < 5 in an area of ∼ 7600 deg 2 of the Sloan Digital Sky Survey (SDSS) footprint with 90°< RA < 270°. Based on a near-infrared/infrared JKW2 color cut, the ELQS selection efficiently uses random forest methods to classify quasars and to estimate photometric redshifts; this scheme overcomes some of the difficulties of pure optical quasar selection at z ≈ 3. As a result, we retain a completeness of > 70% over z ∼ 3.0 − 5.0 at m i 17.5, limited toward fainter magnitudes by the depth of the Two Micron All Sky Survey (2MASS). The presented quasar catalog consists of a total of 270 objects, of which 39 are newly identified in this work with spectroscopy obtained at the Vatican Advanced Technology Telescope and the MMT 6.5 m telescope. In addition to the high completeness, which allowed us to discover new quasars in the already well-surveyed SDSS North Galactic Cap, the efficiency of our selection is relatively high at ∼ 79%. Using 120 objects of this quasar sample we are able to extend the previously measured optical quasar luminosity function (QLF) by one magnitude toward the bright end at 2.8 ≤ z ≤ 4.5. A first analysis of the QLF suggests a relatively steep bright-end slope of β ≈ −4 for this sample. This result contrasts with previous results in the same redshift range, which find a much flatter slope around β ∼ −2.5, but agrees with recent measurements of the bright-end slope at lower and higher redshifts. Our results constrain the bright-end slope at z = 2.8 − 4.5 to β < −2.94 with a 99% confidence.

On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5

“…Also at very bright magnitudes (M 1450 ≤ −27), Schindler et al (2018Schindler et al ( , 2019 find an increase of ∼36% to the number density of QSOs at 3 < z < 5 with respect to the previous results based on 1 The issues of a too early HeII reionization and the high IGM temperature caused by the hard AGN radiation will be discussed in Section 5.…”

Exploring Reionization-era Quasars. III. Discovery of 16 Quasars at 6.4 ≲ z ≲ 6.9 with DESI Legacy Imaging Surveys and the UKIRT Hemisphere Survey and Quasar Luminosity Function at z ∼ 6.7

“…Our least-squares fitting gives Φ * =(3.17±0.85)×10 −9 Mpc −3 mag −1 and β=−2.54± 0.29. At lower redshifts (z5), the QLF has a very steep brightend slope β−3 and a flat faint-end slope α∼−2.0 to −1.5 (e.g., Richards et al 2006;McGreer et al 2013;Yang et al 2016;Schindler et al 2018 2.41 0.08 0.10 at M 1450 −29.0, which is similar to the single power-law fitting at −29.10 M 1450 −24.3 by Jiang et al (2016). We measured the single power-law QLF slope to be β=−2.35±0.22 at z=6.7 using a sample of quasars with −27.6<M 1450 < −25.5.…”

Exploring Reionization-Era Quasars III: Discovery of 16 Quasars at $6.4\lesssim z \lesssim 6.9$ with DESI Legacy Imaging Surveys and UKIRT Hemisphere Survey and Quasar Luminosity Function at $z\sim6.7$

“…At lower redshifts (z 5), the QLF has a very steep bright-end slope β ≤ −3 and a flat faint-end slope α ∼ −2.0 − −1.5 (e.g. Richards et al 2006;McGreer et al 2013;Yang et al 2016;Schindler et al 2018). Jiang et al (2016) measured a slightly flatter bright-end slope of β = −2.8 ± 0.2 at z ∼ 6 with SDSS quasars brighter than M 1450 = −25.3 (also see Willott et al 2010).…”