The 2dF QSO Redshift Survey -- I. The optical luminosity function of quasi-stellar objects

We present a determination of the optical luminosity function of quasi-stellar objects (QSOs) and its cosmological evolution with redshift for a sample of over 6000 QSOs identified primarily from the first observations of the 2dF QSO Redshift Survey (2QZ). For QSOs with 226 , M B , 223 and 0X35 , z , 2X3Y we find that pure luminosity evolution (PLE) models provide an acceptable fit to the observed redshift dependence of the luminosity function (LF). The LF is best fitted by a two-power-law function of the form FL B G L B aL * B a L B aL * B b 21 X Exponential luminosity evolution models, both as a function of look-back time, L * B z L * B 0 e k 1 t Y and as a general second-order polynomial, L * B z G 10 k 1 zk 2 z 2 Y were found to provide acceptable fits to the data set comprising the 2QZ and the Large Bright Quasar Survey. Exponential evolution with look-back time is preferred for q 0 0X05Y while the polynomial evolution model is preferred for q 0 0X5X The shape and evolution of the LF at low redshifts z , 0X5 and/or high luminosities, not currently well sampled by the 2QZ survey, may show departures from pure luminosity evolution, but the results presented here show that, over a significant range of redshift, PLE is a good description of QSO evolution.