| It has become increasingly clear that there is an inherent link between the growth of a galaxy's super massive-black hole and the formation of stars that comprise its bulge. Since QSOs are the manifestation of rapid black hole growth, proper measurement of the QSO luminosity function (QLF) and its evolution with redshift are vitally important for constraining galaxy formation models. At low redshift (z < 2.2), recent surveys have provided accurate measurements of the QLF from the brightest known QSOs to luminosities below typical L* galaxies. At high redshift however, only the bright end of the QLF has been measured and suffers from significant selection effects. The SWIRE Legacy Survey, with its wide-area, deep optical and infrared data can, for the first time, accurately measure the luminosity function of faint QSOs at high redshift.;We present a new QSO template, spanning the ultraviolet to the mid-infrared. We then present optical/IR color criteria for efficient selection of QSOs at 2.8 < z 4.8. The completeness of the resulting sample is assessed through simulations of the QSO SEDs and line-of-sight variations in the intergalactic medium (IGM). Spectroscopic redshifts for 20 objects are presented, including 17 previously unknown high redshift QSOs with 2.8 < z < 3.9. The sample reliability of our z ∼ 3 sample is nearly ∼ 100% while the z ∼ 4 sample suffers from contamination, with a reliability of ∼ 70%.;We measure the luminosity function at z ∼ 3.2 with 102 QSOs (r' < 22) in our first 11.2 deg2 analyzed. Our resulting luminosity function has smaller errors and requires smaller completeness corrections than previous surveys. We fit a faint end slope, beta = -1.45, consistent with recent measurements at low redshift and ruling out preliminary measurements indicating a shallower faint end slope at high redshift. Therefore, within our measurement errors, the faint end slope has not changed significantly from z ∼ 3.5 to the present. Furthermore, our measured QSO space densities are lower, by a factor ∼ 2, than earlier studies, indicating that the epoch of peak QSO space densities is at lower redshift than the previously determined value of z * ∼ 2.75. |
