The Low Surface Brightness Extent of the Fornax Cluster

We have used a large format CCD camera to survey the nearby Fornax clusterand its immediate environment for low luminosity low surface brightnessgalaxies. Recent observations indicate that these are the most dark matterdominated galaxies known and so they are likely to be a good tracer of the darkmatter in clusters. We have identified large numbers of these galaxiesconsistent with a steep faint end slope of the luminosity function (alpha~ -2)down to MB ~ -12. These galaxies contribute almost the same amount to the totalcluster light as the brighter galaxies and they have a spatial extent that issome four times larger. They satisfy two of the important predictions of N-bodyhierarchical simulations of structure formation using dark halos. Theluminosity (mass ?) function is steep and the mass distribution is moreextended than that defined by the brighter galaxies. We also find a largeconcentration of low surface brightness galaxies around the nearby galaxyNGC1291.Comment: 16 pages, 6 figure