We present the first measurement of the faint end of the QSO luminosity function at z = 3. The QSOs, which range from M_(1450) = -21 to M_(1450) = -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 β_l = 1.24 +- 0.07 (Φ ∝ L~(-β_l)), flatter than the value of β_l = 1.64 +- 0.18 measured at lower redshift. The integrated rest 1450 A UV luminosity of z = 3 QSOs is only 50% of most previous estimates and only approx= 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 J_(912) at z ～ 3, J_(912) approx= 2.4 x 10~(-22) ergs s~(-1) cm~(-2) Hz~(-1). This estimate, which we regard as an upper limit, remains consistent with rough estimates of J_(912) based on the Lyα forest "proximity effect."
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机译：我们提出了在z = 3时对QSO光度函数微弱末端的首次测量。在17个场中发现了QSO，范围从M_（1450）= -21到M_（1450）= -27，总计0.43度2.使用多色选择标准（Lyman断裂技术）和分光镜随访。我们发现，亮度函数的微弱末端斜率是β_1= 1.24 +-0.07（ΦL L〜（-β_1）），比在较低红移下测得的β_1= 1.64±0.18的值平坦。 z = 3 QSO的剩余1450 A UV积分仅是以前估计的50％，而在相同的红移下，只有Lyman断裂星系产生的8％。假设来自微弱QSO的电离光子能够像明亮的QSO一样成功地逃离它们的宿主星系，我们估计QSO在z〜3时对电离通量J_（912）的总贡献，J_（912）大约为2.4 x 10〜（ -22）ergs s〜（-1）cm〜（-2）Hz〜（-1）。我们认为这是一个上限，但与基于Lyα森林的“邻近效应”对J_（912）的粗略估计保持一致。
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