High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
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DOI：
10.1086/527025
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发表时间：
2007-11
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通讯作者：
B. Siana;Maria del Carmen Polletta;H. Smith;C. Lonsdale;E. González-Solares;D. Farrah;T. Babbedge;M. Rowan‐Robinson;J. Surace;D. Shupe;F. Fang;A. Franceschini;S. Oliver
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作者：
B. Siana;Maria del Carmen Polletta;H. Smith;C. Lonsdale;E. González-Solares;D. Farrah;T. Babbedge;M. Rowan‐Robinson;J. Surace;D. Shupe;F. Fang;A. Franceschini;S. Oliver
我们使用一个简单的光学/红外（IR）测光选择高红移类星体，确定一个莱曼突破的光学测光，并需要一个红色的IR颜色，以区分类星体从共同的闯入者。在斯皮策广域河外红外线巡天（SWIRE）遗留巡天的ELAIS-N1（EN 1）和ELAIS-N2（EN 2）场中，搜索得到了100个z ≥ 3（U-脱落）类星体候选者，19 < r′ < 22，11.7 deg 2。选择z <3是可靠的，10个候选者的光谱追踪证实它们都是2.83 < z < 3.44的类星体。我们发现我们的z <4（g′-dropout）样本具有不可靠性和不完整性，但在3.50 < z < 3.89处存在7个先前未识别的类星体。详细的模拟表明，我们的z <3的完整性在3.0 < z < 3.5时为~80%-90%，明显优于SDSS在这些红移处的~30%-80%的完整性。由此得到的光度函数比SDSS弱2等，其暗端斜率为β = − 1.42 ± 0.15，与在较低红移时测得的值一致。因此，我们没有看到类星体光度函数的暗端斜率演化的证据。包括SDSS类星体样本在内，我们现在已经直接测量了类星体的空间密度，这些空间密度占z = 3的类星体紫外光度密度的70%。我们得到了类星体在z = 3.2，r = 4.8 × 10−13 s−1处的最大氢光电离速率，大约是通过对Lyα森林的研究推断出的总速率的一半。因此，恒星形成的星系和类星体必须贡献的光致电离的星系际介质中的H I在z 3。
We use a simple optical/infrared (IR) photometric selection of high-redshift QSOs that identifies a Lyman break in the optical photometry and requires a red IR color to distinguish QSOs from common interlopers. The search yields 100 z ∼ 3 (U-dropout) QSO candidates with 19 < r′ < 22 over 11.7 deg2 in the ELAIS-N1 (EN1) and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. The z ∼ 3 selection is reliable, with spectroscopic follow-up of 10 candidates confirming that they are all QSOs at 2.83 < z < 3.44. We find that our z ∼ 4 (g′-dropout) sample suffers from both unreliability and incompleteness but present seven previously unidentified QSOs at 3.50 < z < 3.89. Detailed simulations show our z ∼ 3 completeness to be ~80%-90% from 3.0 < z < 3.5, significantly better than the ~30%-80% completeness of the SDSS at these redshifts. The resulting luminosity function extends 2 mag fainter than SDSS and has a faint-end slope of β = − 1.42 ± 0.15, consistent with values measured at lower redshift. Therefore, we see no evidence for evolution of the faint-end slope of the QSO luminosity function. Including the SDSS QSO sample, we have now directly measured the space density of QSOs responsible for ~70% of the QSO UV luminosity density at z ∼ 3. We derive a maximum rate of H I photoionization from QSOs at z ∼ 3.2, Γ = 4.8 × 10−13 s−1, about half of the total rate inferred through studies of the Lyα forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of H I in the intergalactic medium at z ∼ 3.