2.2. Projected Surveys
The first quantitative discussions of comic inhomogeneity came through a study, mainly by Peebles and his collaborators (see LSSU), of various catalogues of the positions of galaxies on the sky. The famous 1.8 power law behaviour of the correlation function was discovered from the analysis of such catalogues, and the consistency of the results from different catalogues was interpreted as strong evidence that the clustering was indeed a cosmological effect (and not due to foreground obscuration, for example) and that the clustering was homogeneous as a function of the depth of the catalogue. Whereas the 1.8 power law could be consistently identified, the break away from that law on larger scales (the cutoff) was harder to identify with confidence. In the analysis of the Lick survey Groth and Peebles (1977) found a cutoff that corresponded rather closely with the angular scale of the individual photographic plates and that lead to some skepticism about exactly where the feature was (de Lapparent et al., 1989).
Recently, Maddox et al. (1990a, c) have created a catalogue of some 2 million galaxies based on scans of the UK Schmidt J-survey plates with the SERC Automatic Plate Measuring machine (APM). The catalogue covers some 4300 square degrees and reaches to magnitude J = 20.5. It effectively penetrates to a depth of some 600h-1 Mpc. The two point correlation function for this catalogue (Maddox et al., 1990b) shows results that are consistent with the Lick catalogue results in the 1.8 power law regime, but the cutoff is quite different. The cutoff is not at all as abrupt as the Lick catalogue analysis seems to imply, and there is substantial power on very large scales. In fact there is so much power on these large scales that it is difficult to reconcile the predictions of the standard cold dark matter numerical simulations with the data.