The 2dF QSO Redshift Survey - III. The input catalogue

The 2dF QSO Redshift Survey (2QZ) has obtained redshifts for in excess of 23000 QSOs selected by their u', b_J, r colours using the 2-degree Field (2dF) facility at the Anglo-Australian Telescope (AAT). In this paper, we describe the creation of the input catalogue from UK Schmidt photographic plates. All the plate materials used are described along with the techniques developed for flat-fielding variations in the photometric response of photographic emulsions. The selection criteria used for the survey are defined and their rationale discussed. Finally, several simple astrometric and photometric tests are performed. These demonstrate that, over the majority of the parameter space covered by this survey (18.25 < b_J<= 20.85, 0.3 <~z<~ 2.2), the pairwise rms error in the astrometry is 0.4 arcsec (implying independent position errors of ~0.3 arcsec) with no evidence of systematic errors greater than 0.3 arcsec. The photometry is found to be better than 0.15 mag rms over most of the survey and is at worst ~=0.2 mag rms. The completeness with respect to previous QSO surveys is at least 90 per cent. All photometric and astrometric data for the catalogue are now publicly available. We also make available the full u', b_J, r catalogue of three million 16 <~b_J<~ 22 stellar sources from which the 2QZ catalogue was derived. Both this and the 2QZ input catalogue are available from http://www.2dfquasar.org/.