Monday 22 June at 3:30pm

Jonathan Davies - Univ of Wales, Cardiff

"Dwarf Galaxies in the local universe"

ABSTRACT:"We have developed a technique to search for Low Surface Brightness Galaxies (LSBGs) in the local Universe using APM scan data of UK Schmidt photgraphic plates. We optimised our selection criteria by surveying the known LSBGs in the Fornax Cluster. The galaxies we detect are brighter than 20 B mag, have scale sizes greater that 3 arcseconds and central surface brightness fainter than 22.5 mag/square arcseconds. In total 2435 LSBGs were detected over an area of 2187 sq deg. The survey covers the Fornax Cluster, the NGC 1400, Sculptor and Dorado Groups and the field in between. We have estimated the background contamination by modelling the background population, by using a limited redshift sample and by comparing our Fornax data with previous observations. The results indicate a contamination of about 0.5 galaxies per sq deg. The number density of Fornax LSBGs drops exponentially with radius from the cluster centre with a scale length of 1.25 deg, while the bright galaxies have a scale length ~3 times shorter. A correlation analysis of the sample indicates that our galaxies are much more strongly clustered than the general faint population (at the same magnitude limit) but less so than the bright nearby RC3 galaxies (by a factor of ~3) hence we deduce that the LSBGs are associated with the bright galaxies, but distributed over larger scales. We have compared our observations with a fading model explanation of the faint galaxy number counts. This model predicts ~1.7 galaxies per sq deg while we detect ~0.4 per sq deg. Either the fading models are incorrect or there is strong differential fading between clusters and the field."