DES J0454-4448: discovery of the first luminous z ≥ 6 quasar from the Dark Energy Survey

Abstract : We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the z_AB, Y_AB = 20.2, 20.2 (M₁₄₅₀ = -26.5) quasar DES J0454-4448 with a redshift of z = 6.09±0.02 based on the onset of the Ly α forest and an H I near zone size of 4.1_{-1.2}^{+1.1} proper Mpc. The quasar was selected as an i-band drop out with i-z = 2.46 and z_AB < 21.5 from an area of ∼300 deg². It is the brightest of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i-z and z-Y colours. The quasar is detected by WISE and has W1_AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z_AB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ∼ 6. DES when completed will have imaged ∼5000 deg² to Y_AB = 23.0 (5σ point source) and we expect to discover 50-100 new quasars with z > 6 including 3-10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.