Correlation analyses of deep galaxy samples - III

Estimates of the two-point angular correlation function, w(θ), are presented for galaxy samples obtained from COSMOS machine measurements of 1.2-m UK Schmidt telescope (UKST) and 4-m Anglo–Australian telescope (AAT) plates. The ten UKST plates measured cover an area of sky of ∼170 square degrees, some four times larger than any previous study to these depths. All of the estimated w(θ) are consistent with a −0.8 power-law slope at small scales. At larger angular scales a break from the power-law behaviour is seen in the UKST w(θ) corresponding to a spatial separation of $$3h^{-1}\enspace \text {Mpc}\enspace (H_0=100h\enspace \text {km}\enspace \text s^{-1}\enspace \text {Mpc}^{-1})$$ in agreement with the earlier results of Shanks et al. The AAT plates allow the correlation analyses to be carried out to 24 mag in the blue (b_J) passband and 22 mag in the red (r_F) passband. It is observed that the correlation function amplitude scaling relation in both passbands is very similar. This allows us to add an important additional constraint to the modelled scaling relation as well as to the number–magnitude, n(m), count models. It is found that the observed clustering amplitudes at these depths are lower than those predicted using well-determined models that assume no clustering evolution. This result must however, remain tentative until larger areas of sky are surveyed at the AAT plate depths in order to better constrain the observed scaling relation.