The large area KX quasar catalogue: I. Analysis of the photometric
  redshift selection and the complete quasar catalogue
  The results of a large area, ~600 deg^2, K-band flux-limited spectroscopic
survey for luminous quasars are presented. The survey utilises the UKIRT
Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) in regions of sky
within the Sloan Digital Sky Survey (SDSS) footprint. The K-band excess (KX) of
all quasars with respect to Galactic stars is exploited in combination with a
photometric redshift/classification scheme to identify quasar candidates for
spectroscopic follow-up observations. The data contained within this
investigation will be able to provide new constraints on the fraction of
luminous quasars reddened by dust with E(B-V)<=0.5 mag. The spectroscopic
sample is defined using the K-band, 14.0<=K<=16.6, and SDSS i-band limits of
i=19.5, 19.7 and 22.0 over sky areas of 287, 150 and 196 deg^2, respectively.
The survey includes >3200 known quasars from the SDSS and more than 250
additional confirmed quasars from the KX-selection. A well-defined sub-sample
of quasars in the redshift interval 1.0<=z<=3.5 includes 1152 objects from the
SDSS and 172 additional KX-selected quasars. The quasar selection is >95 per
cent complete with respect to known SDSS quasars and >95 per cent efficient,
largely independent of redshift and i-band magnitude. The properties of the new
KX-selected quasars confirm the known redshift-dependent effectiveness of the
SDSS quasar selection and provide a sample of luminous quasars experiencing
intermediate levels of extinction by dust. The catalogue represents an
important step towards the assembly of a well-defined sample of luminous
quasars that may be used to investigate the properties of quasars experiencing
intermediate levels of dust extinction within their host galaxies or due
intervening absorption line systems.
