The z ~ 3 QSO Luminosity Function with SWIRE

Abstract

We use a simple optical/infrared photometric selection of high redshift QSOs which identifies a Lyman Break in the optical and requires a red IRAC color to distinguish QSOs from common interlopers. We find 100 U-dropout (z ~ 3) QSO candidates with r′ < 22 within 11.2 deg^2 in the ELAIS-N1 & ELAIS-N2 fields in the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. Spectroscopy of 10 candidates shows that they are all QSOs with 2.83 < z < 3.44. We use detailed simulations which incorporate variations in QSO SEDs, IGM transmission and imaging depth to derive a completeness of 85- 90% between 3.0 < z < 3.4. The resulting luminosity function is two magnitudes fainter than SDSS and, when combined with those data, gives a faint end slope β = 1.62±0.18, consistent with measurements at z < 2 and steeper than initial measurements at the same redshift.