COMPARISON OF THE LARGE-SCALE CLUSTERING IN THE APM AND THE EDSGC GALAXY SURVEYS

Clustering statistics are compared for the Automatic Plate Machine (AP M) 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 A PM and COSMOS microdensitometers, respectively. The comparison of thes e catalogues is a rare practical opportunity to study systematic error s, 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 t o sixth order. On larger scales there is a small disagreement owing to edge effects in the EDSGC, which covers a smaller area. On smaller sc ales, we find a significant disagreement which can only be attributed to differences in the construction of the surveys. Visual inspection o f nine high-density regions reveals that a likely reason is the dissim ilar deblending of crowded fields. The overall agreement of the APM an d EDSGC surveys is encouraging, and shows that the results for interme diate scales should be fairly robust. On the other hand, the systemati c deviations found at small scales are significant in a regime where c omparison with theory and simulations is possible. This is an importan t fact to bear in mind when planning the construction of future digiti zed galaxy catalogues.