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We describe a new, deep photographic survey of the Virgo Cluster which uses multiple exposures on Tech Pan film with the United Kingdom Schmidt Telescope to probe the dwarf population to fainter surface brightness limits than previous surveys. We have identified galaxies having sizes (≥ 3 arcsec scale length) and surface brightnesses (≤ 24.5 R mag arcsec−2) characteristic of those expected for dwarf spheroidal galaxies in the cluster. The survey is providing substantial samples of extremely low luminosity galaxies outside the environment of the Local Group and nearby groups for the first time. An initial study of two small areas has found dwarf spheroidal candidates in large numbers (500 deg−2) which indicate a steep, continuously rising luminosity function at low luminosities.

Recent studies have demonstrated that many galaxy clusters have luminosity functions (LFs) which are steep at the faint end. However, it is equally clear that not all clusters have identical LFs. In this paper we explore whether the variation in LF shape correlates with other cluster or environmental properties.

We report on a new survey for low surface brightness galaxies using Kodak Tech Pan 4415 film on the UKST, and demonstrate the advantages of this film over conventional IIIa plates when searching for faint, extended objects. Recent experiments with films of the Virgo cluster have shown that the noise per pixel in deep exposures is only 0.7 % of sky, enabling known objects to be traced out to an isophote around 27 Rµ. In addition, a preliminary survey has revealed several new galaxies with central surface brightnesses around 24 Rµ. With the digital coaddition of several films, we expect to be able to measure objects out to the 28 Rµ isophote and detect galaxies with central surface brightnesses as faint as ∼ 25 Rµ, i.e. below 3 % of sky.