The Faint End of the Qso Luminosity Function At

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 using multicolor selection criteria (the Lyman break technique) and spectroscopic followup. We find that the faintend slope of the luminosity function is βl = 1.24± 0.07 (Φ ∝ L l), flatter than the value of βl = 1.64 ± 0.18 measured at lower redshift. The integrated rest 1450Å UV luminosity of z = 3 QSOs is only 50% of most previous estimates, and is 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 Hz. This estimate, which we regard as an upper limit, remains consistent with rough estimates of J912 based on the Lyman α forest “proximity effect.” Based, in part, on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation. Packard Fellow