摘要：This is the fourth paper in a series of publications aiming at discovering quasars at the epoch of reionization. In this paper, we expand our search for z∼7 quasars to the footprint of the Dark Energy Survey (DES) Data Release One (DR1), covering ∼5000deg 2 of a new area. We select z∼7 quasar candidates using deep optical, near-infrared (near-IR) and mid-infrared (mid-IR) photometric data from the DES DR1, the VISTA Hemisphere Survey, the VISTA Kilo-degree Infrared Galaxy survey, the UKIRT InfraRed Deep Sky Surveys—Large Area Survey (ULAS), and the unblurred coadds from the Wide-field Infrared Survey Explore (WISE) images (unWISE). The inclusion of DES and unWISE photometry allows the search to reach ∼1mag fainter, comparing to our z 6.5 quasar survey in the northern sky. We report the initial discovery and spectroscopic confirmation of six new luminous quasars at z>6.4, including an object at z=7.02, the fourth quasar yet known at z>7, from a small fraction of candidates observed thus far. Based on the recent measurement of z∼6.7 quasar luminosity function using the quasar sample from our survey in the northern sky, we estimate that there will be 55 quasars at z>6.5 at M 1450 <−24.5 in the full DES footprint.
