The 2dF-SDSS LRG and QSO Survey: the QSO luminosity function at
  0.4<z<2.6
  We present the QSO luminosity function of the completed 2dF-SDSS LRG and QSO
(2SLAQ) survey, based on QSOs photometrically selected from Sloan Digital Sky
Survey imaging data and then observed spectroscopically using the 2dF
instrument on the Anglo-Australian Telescope. We analyse 10637 QSOs in the
redshift range 0.4<z<2.6 to a g-band flux limit of 21.85 (extinction corrected)
and an absolute continuum magnitude of Mg(z=2)<-21.5. This sample covers an
area of 191.9 deg^2.
  The binned QSO luminosity function agrees with that of the brighter SDSS main
QSO sample, but extends ~2.5 mags fainter, clearly showing the flattening of
the luminosity function towards faint absolute magnitudes. 2SLAQ finds an
excess of QSOs compared to the 2dF QSO Redshift Survey at g>20.0, as found
previously by Richards et al. (2005). The luminosity function is consistent
with other previous, much smaller, samples produced to the depth of 2SLAQ.
  By combining the 2SLAQ and SDSS QSO samples we produce a QSO luminosity
function with an unprecedented combination of precision and dynamic range. With
this we are able to accurately constrain both the bright and faint ends of the
QSO LF. While the overall trends seen in the evolution of the QSO LF appear
similar to pure luminosity evolution, the data show very significant departures
from such a model. Most notably we see clear evidence that the number density
of faint QSOs peaks at lower redshift than bright QSOs: QSOs with Mg>-23 have
space densities which peak at z<1, while QSOs at Mg<-26 peak at z>2. By fitting
simple luminosity function models in narrow Mg intervals we find that this
downsizing is significant at the 99.98 per cent level (abridged).
