Quasars from a complete spectroscopic survey

With the advent of multi-fibre spectrographs such as the 'Two-Degree Field' (2dF) instrument at the Angle-Australian Telescope, quasar surveys that ar e free of any preselection of candidates and any biases this implies have b ecome possible for the first time. The first of these is that which is bein g undertaken as part of the Fornax Spectroscopic Survey, a survey of the ar ea around the Fornax Cluster of galaxies, and aims to obtain the spectra of all objects in the magnitude range 16.5 < b(j) < 19.7. To date, 3679 objec ts in the central pi -deg(2) area have been successfully identified from th eir spectral characteristics. Of these, 71 are found to be quasars, 61 with redshifts 0.3 < z < 2.2 and 10 with redshifts z > 2.2. Using this complete quasar sample, a new determination of quasar number counts is made, enabli ng an independent check of existing quasars surveys. Cumulative counts per square degree at a magnitude limit of b(j) < 19.5 are found to be 11.5 +/- 2.2 for 0.3 < z < 2.2, 2.22 +/- 0.93 for z > 2.2 and 13.7 +/- 3.1 for z > 0 .3. Given the likely detection of extra quasars in the Fornax survey, we make a more detailed examination of existing quasar selection techniques. First, looking at the use of a stellar criterion, four of the 71 quasars are 'non- stellar' on the basis of the automated plate measuring facility (APM) b(j) classification, however inspection shows all are consistent with stellar, b ut misclassified due to image confusion. Examining the ultraviolet excess a nd multicolour selection techniques, for the selection criteria investigate d, ultraviolet excess would find 69 +/- 6 per cent of our 0.3 < z < 2.2 qua sars and only 50(-18)(+14), per cent of our z > 2.2 quasars, while the comp leteness level for multicolour selection is found to be 90(-4)(+3) per cent for 0.3 < z < 2.2 quasars and 80(-12)(+14) per cent for z > 2.2 quasars. T he extra quasars detected by our all-object survey thus have unusually red star-like colours, and this appears to be a result of the continuum shape r ather than any emission features. An intrinsic dust extinction model may, a t least partly, account for the red colours.