The Faint End of the QSO Luminosity Function at z = 3

We present the first measurement of the faint end of the QSO luminosity function at z = 3. The QSOs, which range from M1450 = -21 to M1450 = -27, were discovered in 17 fields totaling 0.43 deg 2 using multicolor selection criteria (the Lyman break technique) and spectroscopic follow-up. We find that the faint-end slope of the luminosity function is βl = 1.24 ± 0.07 (Φ ∝ L), flatter than the value of βl = 1.64 ± 0.18 measured at lower redshift. The integrated rest 1450 Å UV luminosity of z = 3 QSOs is only 50% of most previous estimates and only ≃8% of that produced by Lyman break galaxies at the same redshifts. Assuming that ionizing photons from faint QSOs are as successful in escaping their host galaxies as bright QSOs, we estimate the total contribution of QSOs to the ionizing flux J912 at z ~ 3, J912 ≃ 2.4 × 10-22 ergs s-1 cm-2 Hz-1. This estimate, which we regard as an upper limit, remains consistent with rough estimates of J912 based on the Lyα forest "proximity effect."