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

Barnett, R.; Warren, S. J.; Mortlock, D. J.; Cuby, J. -G.; Conselice, C.; Hewett, P. C.; Willott, C. J.; Auricchio, N.; Balaguera-Antolinez, A.; Baldi, M.; Bardelli, S.; Bellagamba, F.; Bender, R.; Biviano, A.; Bonino, D.; Bozzo, E.; Branchini, E.; Brescia, M.; Brinchmann, J.; Burigana, C.; Camera, S.; Capobianco, V.; Carbone, C.; Carretero, J.; Carvalho, C. S.; Castander, F. J.; Castellano, M.; Cavuoti, S.; Cimatti, A.; Cledassou, R.; Congedo, G.; Conversi, L.; Copin, Y.; Corcione, L.; Coupon, J.; Courtois, H. M.; Cropper, M.; Da Silva, A.; Duncan, C. A. J.; Dusini, S.; Ealet, A.; Farrens, S.; Fosalba, P.; Fotopoulou, S.; Fourmanoit, N.; Frailis, M.; Fumana, M.; Galeotta, S.; Garilli, B.; Gillard, W.; Gillis, B. R.; Gracia-Carpio, J.; Grupp, F.; Hoekstra, H.; Hormuth, F.; Israel, H.; Jahnke, K.; Kermiche, S.; Kilbinger, M.; Kirkpatrick, C. C.; Kitching, T.; Kohley, R.; Kubik, B.; Kunz, M.; Kurki-Suonio, H.; Laureijs, R.; Ligori, S.; Lilje, P. B.; Lloro, I.; Maiorano, E.; Mansutti, O.; Marggraf, O.; Martinet, N.; Marulli, F.; Massey, R.; Mauri, N.; Medinaceli, E.; Mei, S.; Mellier, Y.; Metcalf, R. B.; Metge, J. J.; Meylan, G.; Moresco, M.; Moscardini, L.; Munari, E.; Neissner, C.; Niemi, S. M.; Nutma, T.; Padilla, C.; Paltani, S.; Pasian, F.; Paykari, P.; Percival, W. J.; Pettorino, V.; Polenta, G.; Poncet, M.; Pozzetti, L.; Raison, F.; Renzi, A.; Rhodes, J.; Rix, H. -W.; Romelli, E.; Roncarelli, M.; Rossetti, E.; Saglia, R.; Sapone, D.; Scaramella, R.; Schneider, P.; Scottez, V.; Secroun, A.; Serrano, S.; Sirri, G.; Stanco, L.; Sureau, F.; Tallada-Crespi, P.; Tavagnacco, D.; Taylor, A. N.; Tenti, M.; Tereno, I.; Toledo-Moreo, R.; Torradeflot, F.; Valenziano, L.; Vassallo, T.; Wang, Y.; Zacchei, A.; Zamorani, G.; Zoubian, J.; Zucca, E.

doi:10.1051/0004-6361/201936427

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; φ) with redshift, φâ 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 to JAB ∼ 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 ∼25 quasars beyond the current record of z = 7.5, including ∼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, 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 at JAB ∼ 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 1σ uncertainty of 0.07.