期刊
ASTROPHYSICAL JOURNAL
卷 675, 期 1, 页码 49-70出版社
IOP PUBLISHING LTD
DOI: 10.1086/527025
关键词
intergalactic medium; quasars : general
资金
- Science and Technology Facilities Council [ST/F005245/1, PP/C002229/1, ST/F001967/1] Funding Source: researchfish
- STFC [ST/F001967/1, ST/F005245/1] Funding Source: UKRI
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 similar to 3 ( U-dropout) QSO candidates with 19 < r ' < 22 over 11.7 deg(2) in the ELAIS-N1 (EN1) and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. The z similar to 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 similar to 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 similar to 3 completeness to be similar to 80%-90% from 3.0 < z < 3.5, significantly better than the similar to 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 beta = -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 similar to 70% of the QSO UV luminosity density at z similar to 3. We derive a maximum rate of H I photoionization from QSOs at z similar to 3.2, Gamma = 4.8 x 10(-13) s(-1), about half of the total rate inferred through studies of the Ly alpha forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of H I in the inter-galactic medium at z similar to 3.
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