Hidden Galaxies in the Fornax Cluster

We are using the Multibeam 21-cm receiver on the Parkes Radio Telescope combined with the optical Two-degree-Field (2dF) spectrograph of the Angle-Australian Telescope to obtain the first complete spectroscopic sample of the Fornax cluster. In the optical, the survey is unique in that all objects ("stars" and "galaxies") within our magnitude limits (16.(m)5 less than or equal to B-J less than or equal to 19.(m)7) are measured, producing the most complete survey of cluster members, irrespective of surface-brightness. We have detected two new classes of high surface-brightness dwarf galaxy in the cluster. With 2dF we have discovered a population of very low luminosity (Mg approximate to -12(m)) objects which are unresolved from the ground and may be the stripped nuclei of dwarf galaxies; they are unlike any known galaxies. In a survey of the brighter (16.(m)5 less than or equal to B-J less than or equal to 18.(m)0) galaxies with the FLAIR-II spectrograph, we have found a number of new high surface-brightness dwarf galaxies. We show that the fraction of star-forming dwarf galaxies in the cluster is about 30%, about twice that implied by earlier morphological classifications. By using a new "basket weave" scanning pattern, our radio observations have a greatly improved sensitivity compared to the standard Multibeam survey by using a new "basket weave" scanning pattern. Our initial analysis shows that we are detecting new cluster members with HI masses of order 10(8) M-circle dot and HI mass-to-light ratios of 1-2 M-circle dot/L-circle dot.