The Monopole Moment of the Three-Point Correlation Function of the 2-degree Field Galaxy Redshift Survey

We measure the monopole moment of the three-point correlation function on scales $1\mpc-70\mpc$ in the Two degree Field Galaxy Redshift Survey (2dFGRS). Volume limited samples are constructed using a series of integral magnitudes bins between $M = -18 ... -22$. 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 $-21 \sim -20$ volume limited sample we find $\sigma_8 = 0.93^{+0.06}_{-0.2}$, $b = 1.04^{+0.23}_{-0.09}$, and $b_2 = -0.06^{+0.003}_{-0.001}$. 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 previous findings of the bias evolution in the 2dFGRS.