The monopole moment of the three-point correlation function of the two-degree Field Galaxy Redshift Survey

We measure the monopole moment of the three-point correlation function on scales 1-70h^-1Mpc in the two-degree Field Galaxy Redshift Survey (2dFGRS). Volume-limited samples are constructed using a series of integral magnitude bins between M=-18 to -22. Our measurements with a novel edge-corrected estimator represent most, if not all, three-point level monopole or angular averaged information in the catalogue. We fit a perturbative non-linear bias model to a joint data vector formed from the estimated two- and three-point correlation functions. Two different models are used: an analytic model based on Eulerian perturbation theory including bias and redshift distortions and a phenomenological bias model based on the direct redshift space measurements in the large Virgo simulations. To interpret the clustering results, we perform a three-parameter Gaussian maximum-likelihood analysis. In the canonical -21 to -20 volume-limited sample, we find σ₈= 0.93^+0.06_-0.2, b= 1.04^+0.23_-0.09 and b₂=-0.06^+0.003_-0.001. Our estimate of σ₈ is robust across the different volume-limited samples constructed. These results, based solely on the large-scale clustering of galaxies, are in excellent agreement with previous analyses using the Wilkinson Anisotropy Probe; this is a spectacular success of the concordance model. We also present two-parameter fits for the bias parameters, which are in excellent agreement with the previous findings of the bias evolution in the 2dFGRS.