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We present discovery imaging and spectroscopy for nine new z ∼ 6 quasars found in the Canada–France High-z Quasar Survey (CFHQS) bringing the total number of CFHQS quasars to 19. By combining the CFHQS with the more luminous Sloan Digital Sky Survey sample, we are able to derive the quasar luminosity function from a sample of 40 quasars at redshifts 5.74 < z < 6.42. Our binned luminosity function shows a slightly lower normalization and flatter slope than found in previous work. The binned data also suggest a break in the luminosity function at M1450 ≈ −25. A double power-law maximum likelihood fit to the data is consistent with the binned results. The luminosity function is strongly constrained (1σ uncertainty <0.1 dex) over the range −27.5 < M1450 < −24.7. The best-fit parameters are Φ(M*1450) = 1.14 × 10−8 Mpc−3 mag−1, break magnitude M*1450 = −25.13, and bright end slope β = −2.81. However, the covariance between β and M*1450 prevents strong constraints being placed on either parameter. For a break magnitude in the range −26 < M*1450 < −24, we find −3.8 < β < −2.3 at 95% confidence. We calculate the z = 6 quasar intergalactic ionizing flux and show it is between 20 and 100 times lower than that necessary for reionization. Finally, we use the luminosity function to predict how many higher redshift quasars may be discovered in future near-IR imaging surveys.
Willott et al. (Mon,) studied this question.