Faint Extended X-ray Sources: A new Large Area Survey

We have searched for extended X-ray sources in the ROSAT PSPC archive using the Voronoi Tesslation and Percolation algorithm (VTP). This algorithm detects all significant sources regardless of shape or size, and is particularly suited to finding low surface brightness extended sources which could be missed or wrongly interpreted by other algorithms. In an initial 13 sq deg (66 fields) we have found 22 sources with detected flux $>$7x10$^{-14}$ erg cm$^{-2}$ s$^{-1}$ (0.5-2 keV) and sizes of 1 to 5 arcmin. Optically, they range from a single bright nearby galaxy which has been resolved, an Abell cluster which is revealed to have two (probably merging) components, and groups and clusters of galaxies at estimated redshifts beyond z$=$0.4. This work is part of an ongoing survey with the aims of (a) measuring the low luminosity ($<$10$^{44}$ erg s$^{-1}$), high redshift (z$>$0.2) X-ray luminosity function of clusters, and (b) investigating cluster morphologies and unusual systems (eg `fossil' groups).