Euclidpreparation

Abstract

We provide predictions of the yield of 7 < z < 9 quasars from theEuclidwide survey, updating the calculation presented in theEuclidRed Book in several ways. We account for revisions to theEuclidnear-infrared filter wavelengths; we adopt steeper rates of decline of the quasar luminosity function (QLF; Φ) with redshift, Φ ∝ 10k(z − 6),k = −0.72, and a further steeper rate of decline,k = −0.92; we use better models of the contaminating populations (MLT dwarfs and compact early-type galaxies); and we make use of an improved Bayesian selection method, compared to the colour cuts used for the Red Book calculation, allowing the identification of fainter quasars, down toJAB ∼ 23. Quasars atz > 8 may be selected fromEuclidOYJHphotometry alone, but selection over the redshift interval 7 < z < 8 is greatly improved by the addition ofz-band data from, e.g., Pan-STARRS and LSST. We calculate predicted quasar yields for the assumed values of the rate of decline of the QLF beyondz = 6. If the decline of the QLF accelerates beyondz = 6, withk = −0.92,Euclidshould nevertheless find over 100 quasars with 7.0 < z < 7.5, and ∼25 quasars beyond the current record ofz = 7.5, including ∼8 beyondz = 8.0. The firstEuclidquasars atz > 7.5 should be found in the DR1 data release, expected in 2024. It will be possible to determine the bright-end slope of the QLF, 7 < z < 8,M1450 < −25, using 8 m class telescopes to confirm candidates, but follow-up with JWST or E-ELT will be required to measure the faint-end slope. Contamination of the candidate lists is predicted to be modest even atJAB ∼ 23. The precision with whichkcan be determined over 7 < z < 8 depends on the value ofk, but assumingk = −0.72 it can be measured to a 1σuncertainty of 0.07.