Euclid preparation: V. Predicted yield of redshift 7<z<9 quasars from the wide survey

Understand

We provide predictions of the yield of $7<z<9$ quasars from the Euclid wide survey, updating the calculation presented in the Euclid Red Book in several ways.

• We account for revisions to the Euclid near-infrared filter wavelengths; we adopt steeper rates of decline of the quasar luminosity function (QLF; $\Phi$) with redshift, $\Phi\propto10^{k(z-6)}$, $k=-0.72$, 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 use an improved Bayesian selection method, compared to the colour cuts used for the Red Book calculation, allowing the identification of fainter quasars, down to $J_{AB}\sim23$.
• Quasars at $z>8$ may be selected from Euclid $OYJH$ photometry alone, but selection over the redshift interval $7<z<8$ is greatly improved by the addition of $z$-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 beyond $z=6$.