An automated search for nearby low-surface-brightness galaxies - II. The discussion

An automated search for low-surface-brightness (LSB) galaxies over 2187 deg (2) of sky produced 2435 galaxies. The technique, calibration, background c ontamination, models of the galaxy populations, survey and catalogue were d iscussed in Paper I. In this paper we present an analysis of our results. T he number density of Fornax LSB galaxies drops exponentially with radius fr om the cluster centre with a scalelength of 1.25 degrees while the bright g alaxies have a scalelength of 0.48 degrees. Spectroscopic observations in t he Fornax region reveal that two LSB galaxies are at approximately the same redshift as the Fornax cluster, yet they are six bright galaxy scalelength s from the cluster centre. A correlation analysis of the sample indicates t hat our galaxies are much more strongly clustered (A(omega) = 0.82) than th e general faint population (at the same magnitude limit) but less so than t he bright nearby RC3 galaxies (A(omega) = 2.23) sampled within the same vol ume. This implies that LSB galaxies are associated with bright galaxies, bu t distributed over a larger scale. We have compared our observations with a fading model of the faint galaxy number counts. This model predicts approx imate to 60 galaxies per field while we detect on average 13. Either the fa ding models are incorrect or there is strong differential fading between cl usters and field. The luminosity function of the Fornax cluster has a slope of alpha = -1.58 +/- 0.6. The total luminosity of the Fornax cluster is do minated by bright galaxies with a LSB-to-bright luminosity ratio of 0.02 wh ile the field has a ratio of 0.03.