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 70 h(-1) Mpc 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 sigma(8) = 0.93(-0.2)(+0.06), b = 1.04(-0.09)(+0.23) and b(2) = -0.06(-0.001)(+0.003). Our estimate of sigma(8) 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.