The Las Campanas/AAT Rich Cluster Survey I: Precision and Reliability of the Photometric Catalogue

Abstract

The Las Campanas Observatory and Anglo--Australian Telescope Rich Cluster Survey (LARCS) is a panoramic imaging and spectroscopic survey of an X-ray luminosity-selected sample of 21 clusters of galaxies at 0.07<z<0.16. CCD imaging was obtained in B and R of typically 2-degree wide regions centred on the 21 clusters, and the galaxy sample selected from the imaging is being used for an on-going spectroscopic survey of the clusters with the 2dF spectrograph on the Anglo-Australian Telescope. This paper presents the reduction of the imaging data and the photometric analysis used in the survey. Based on an overlapping area of 12.3 square degrees, we compare the CCD-based LARCS catalogue with the photographic-based galaxy catalogue used for the input to the 2dF Galaxy Redshift Survey (2dFGRS) from the APM, to the completeness of the GRS/APM catalogue, b_J=19.45. This comparison confirms the reliability of the photometry across our mosaics and between the clusters in our survey. This comparison also provides useful information about the properties of the GRS/APM. The stellar contamination in the GRS/APM galaxy catalogue is confirmed to be around 5-10 percent, as originally estimated. However, using the superior sensitivity and spatial resolution in the LARCS survey, we find evidence for four distinct populations of galaxies that are systematically omitted from the GRS/APM catalogue. The characteristics of the `missing' galaxy populations are described, reasons for their absence examined and the impact they will have on the conclusions drawn from the 2dF Galaxy Redshift Survey are discussed.