The Three‐Point Correlation Function of Galaxies Determined from the Two‐Degree Field Galaxy Redshift Survey

In a detailed analysis of the three point correlation function (3PCF) for the 2dF Galaxy Redshift Survey we have accurately measured the 3PCF for galaxies of different luminosity. The 3PCF amplitudes [$Qsu$ or $Qrpu$] of the galaxies generally decrease with increasing triangle size and increase with the shape parameter $v$, in qualitative agreement with the predictions for the clustering of dark matter in popular hierarchical CDM models. The 2dFGRS results agree well with the results of Jing & B"orner for the Las Camapanas Redshift Survey (LCRS), though the measurement accuracy is greatly improved in the present study. The dependence of the 3PCF on luminosity is not significant, but there seems to be a trend for the brightest galaxy sample to have a lower amplitude than the fainter ones. Comparing the measured 3PCF amplitudes [$Qsu$ or $Qrpu$] to the prediction of a WMAP concordance model, we find that the measured values are consistently lower than the predicted ones for dark matter. This is most pronounced for the brightest galaxies, for which about one-half of the predicted $Q$ value provides a good description of $Qrpu$ for the 2dFGRS data. For a less luminous sample, the $Q$ values are also smaller than in the dark matter model on small scales, but on scales larger than $s=8 mpc$ and $r_p=3.25 mpc$ they reach the model values. We discuss implications for current theories of galaxy formation.