High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function

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 deg^2 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 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 7 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 two magnitudes 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 ~70% of the QSO UV luminosity density at z~3. We derive a maximum rate of HI photoionization from QSOs at z~3.2, Gamma = 4.8x10^-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 HI in the intergalactic medium at z~3.

Accepted for publication in ApJ. emulateapj format. 23 pages, 17 figures

References in corpus (5)

• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
• The Direct Detection of Lyman-Continuum Emission from Star-forming Galaxies at z~3
• New Constraints on the Lyman Continuum Escape Fraction at z~1.3
• The VVDS type-1 AGN sample: The faint end of the luminosity function
• The Luminosity Function of high-redshift QSOs - A combined analysis of GOODS and SDSS

Cited by in corpus (20)

• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• The first ultraviolet quasar stacked spectrum at z=2.4 from WFC3
• Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
• Quasars Are Not Light-Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution
• The Subaru high-z quasar survey: discovery of faint z~6 quasars
• High redshift quasars in the COSMOS survey: the space density of z>3 X-ray selected QSOs
• Luminosity Function from dedicated SDSS-III and MMT data of quasars in 0.7<z<4.0 selected with a new approach
• The History and Morphology of Helium Reionization
• Triggering Active Galactic Nuclei in Hierarchical Galaxy Formation: Disk instability vs. Interactions
• Massive black hole evolution models confronting the n-Hz amplitude of the stochastic gravitational wave background
• Quasar UV luminosity function evolution up to z=8
• Second Data Release of the COSMOS Lyman-alpha Mapping and Tomographic Observation: The First 3D Maps of the Detailed Cosmic Web at 2.05<z<2.55
• Fluctuations in the Ionizing Background During and After Helium Reionization
• Galaxy fields of LISA massive black hole mergers in a simulated Universe
• Obscured and powerful AGN and starburst activities at z~3.5
• The Assembly of Black Hole Mass and Luminosity Functions of High-redshift Quasars via Multiple Accretion Episodes
• Properties and merger signatures of galaxies hosting LISA coalescing massive black hole binaries
• Revisiting the Completeness and the Luminosity Function in High-Redshift Low-Luminosity Quasar Surveys
• Optical Selection of Faint AGN in the COSMOS Field
• Strong Lensing by Subhalos in the Dwarf-Galaxy Mass Range II: Detection Probabilities