The Fornax Cluster Spectroscopic Survey ( FCSS ) project utilises the Two-degree field ( 2dF ) multi-object spectrograph on the Anglo-Australian Telescope .
Its aim is to obtain spectra for a complete sample of all 14000 objects with 16.5 \leq b _ { j } \leq 19.7 irrespective of their morphology in a 12 deg ^ { 2 } area centred on the Fornax Cluster .
A sample of 24 Fornax Cluster members has been identified from the first 2dF field ( 3.1 deg ^ { 2 } in area ) to be completed .
This is the first complete sample of cluster objects of known distance with well defined selection limits .
19 of the galaxies ( with –15.8 < M _ { B } < –12.7 ) appear to be conventional dwarf elliptical ( dE ) or dwarf S0 ( dS0 ) galaxies .
The other 5 objects ( with –13.6 < M _ { B } < –11.3 ) are those galaxies which we described in Drinkwater et al .
( 2000b ) and labelled ‘ Ultra-Compact Dwarfs ’ ( UCDs ) .
A major result is that the conventional dwarfs all have scale-sizes \alpha \ga 3 arcsec ( \simeq 300 pc ) .
This apparent minimum scale size implies an equivalent minimum luminosity for a dwarf of a given surface brightness .
This produces a limit on their distribution in the magnitude-surface brightness plane , such that we do not observe dEs with high surface-brightnesses but faint absolute magnitudes .
Above this observed minimum scale-size of 3 arcsec , the dEs and dS0s fill the whole area of the magnitude–surface brightness plane sampled by our selection limits .
The observed correlation between magnitude and surface brightness noted by several recent studies of brighter galaxies is not seen with our fainter cluster sample .
A comparison of our results with the Fornax Cluster Catalog ( FCC ) of Ferguson illustrates that attempts to determine cluster membership solely on the basis of observed morphology can produce significant errors .
The FCC identified 17 of the 24 FCSS sample ( i.e 71 per cent ) as being ‘ cluster ’ members , in particular missing all 5 of the UCDs .
The FCC also suffers from significant contamination : within the FCSS ’ s field and selection limits , 23 per cent of those objects described as cluster members by the FCC are shown by the FCSS to be background objects .