학술논문
High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
Document Type
Article
Author
Source
The Astrophysical Journal; March 2008, Vol. 675 Issue: 1 p49-70, 22p
Subject
Language
ISSN
0004637X; 15384357
Abstract
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 
b = [?] 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, 
G = 4.8 x 10[?]13 s[?]1, about half of the total rate inferred through studies of the Lya forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of H I in the intergalactic medium at 
z [?] 3.
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 b = [?] 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, G = 4.8 x 10[?]13 s[?]1, about half of the total rate inferred through studies of the Lya forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of H I in the intergalactic medium at z [?] 3.