First Discoveries of z > 6 Quasars with the DECam Legacy Survey and UKIRT Hemisphere Survey

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractWe present the first discoveries from a survey of z6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg 2 of sky down to z AB ∼23.0, and UKIDSS and UHS will map the northern sky at 0<decl.<+60°, reaching J VEGA ∼19.6 (5-σ). The combination of these data sets allows us to discover quasars at redshift z7 and to conduct a complete census of the faint quasar population at z6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z6 quasars and one new z=6.63 quasar in our pilot spectroscopic observations. The two new z∼6 quasars are at z=6.07 and z=6.17 with absolute magnitudes at rest-frame wavelength 1450 Å being M 1450 =−25.83 and M 1450 =−25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z6. The new z=6.63 quasar has an absolute magnitude of M 1450 =−25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield ∼200 z∼6 quasars to z AB <21.5, ∼1000 z∼6 quasars to z AB <23, and ∼30 quasars at z>6.5 to J VEGA <19.5.

Quasar Photometric Redshifts and Candidate Selection: A New Algorithm Based on Optical and Mid-infrared Photometric Data

“…We also include some quasars, which are not in the SDSS DR7 or DR12 catalog. A high redshift quasar catalog with 437 z > 4.5 (called the BONUS high redshift sample) was constructed from the literature (Table 1 and Table 3 in Wang et al (2015) and references therein; Table 7 in Bañados et al (2016) and references therein; Jiang et al 2016;Yang et al 2017;Wang et al 2017). …”

“…The 5σ pointsource magnitude limits in g, r, and z will be roughly 24.7, 23.9, and 23.0 mag. With depths of 1.5 − 2.5 mag fainter than in the SDSS, the DELS will be useful in searching for fainter quasars than the SDSS spectroscopic quasars, and also high redshift quasars (Wang et al 2017). In this work, we use the three band (grz) photometry from the DECaLS DR3.…”

Inhomogeneous reionization models in cosmological hydrodynamical simulations

“…In fact, current Lyα forest measurements at z > 4 ( Viel et al 2013a;Iršič et al 2017;D'Aloisio et al 2018b) provide constraints on the power at the relevant scales (10 −3 > k > 10 −1 s km −1 , 10 −1 > k > 10 h/Mpc) and therefore may already tell us something about the effects of inhomogeneous reionization on the IGM at these redshifts. Moreover the past several years have seen a dramatic fivefold increase in the number of z 6 quasars from deep wide-field optical/IR surveys (Willott et al 2010;Bañados et al 2014;Venemans et al 2015b,a;Wang et al 2017). The ongoing spectroscopic follow-up of these objects (e.g.…”

Physical Properties of 15 Quasars at z ≳ 6.5

“…15 We do not consider the quasars VDES J0224-4711 (z 6.50 = ; Reed et al 2017), DELS J104819.09-010940.2 (z 6.63 = ; Wang et al 2017), and J1429-0104 (z 6.80; = Matsuoka et al 2017), which were reported during the final stages of the preparation of this manuscript.…”