Comparison of the large-scale clustering in the APM and the EDSGC galaxy surveys

Clustering statistics are compared for the Automatic Plate Machine (APM) and the Edinburgh/Durham Southern Galaxy Catalogue (EDSGC) angular galaxy surveys. Both surveys were independently constructed from scans of the same adjacent UK IIIa-J Schmidt photographic plates with the APM and COSMOS microdensitometers, respectively. The comparison of these catalogues is a rare practical opportunity to study systematic errors, which cannot be achieved via simulations or theoretical methods. On intermediate scales, 0.degrees 1 < theta < 0.degrees 5, we find good agreement for the cumulants or reduced moments of counts in cells up to sixth order. On larger scales there is a small disagreement owing to edge effects in the EDSGC, which covers a smaller area. On smaller scales, we find a significant disagreement which can only be attributed to differences in the construction of the surveys. Visual inspection of nine high-density regions reveals that a likely reason is the dissimilar deblending of crowded fields. The overall agreement of the APM and EDSGC surveys is encouraging, and shows that the results for intermediate scales should be fairly robust. On the other hand, the systematic deviations found at small scales are significant in a regime where comparison with theory and simulations is possible. This is an important fact to bear in mind when planning the construction of future digitized galaxy catalogues.