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

* Corresponding author
6 SEN - Sénescence et stabilité génomique
DBG - Département Biologie des Génomes
35 Continental Dynamics Laboratory [CAGS Beijing]
CAGS - Institute of Geology [CAGS Beijing]
Abstract : 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, $\Phi$ ∝ 10$^{k(z−6)}$, $k$ = −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 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 to $J_{AB}$ $\sim$23. 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. If the decline of the QLF accelerates beyond z = 6, with $k$ = −0.92, Euclid should nevertheless find over 100 quasars with 7.0 <  z <  7.5, and $\sim$25 quasars beyond the current record of z = 7.5, including $\sim$8 beyond z = 8.0. The first Euclid quasars at z >  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, $M_{1450}$ <  −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 at $J_{AB}$$\sim$ 23. The precision with which k can be determined over 7 <  z <  8 depends on the value of $k$, but assuming k = −0.72 it can be measured to a 1$\sigma$ uncertainty of 0.07.
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Cited literature [115 references]

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R. Barnett, S. J. Warren, D. J. Mortlock, J.-G. Cuby, C. Conselice, et al.. Euclid preparation: V. Predicted yield of redshift 7 < z < 9 quasars from the wide survey. Astronomy and Astrophysics - A&A, EDP Sciences, 2019, 631, pp.A85. ⟨10.1051/0004-6361/201936427⟩. ⟨cea-02334278⟩

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