Clustering of Luminous Red Galaxies III: Detection of the Baryon Acoustic Peak in the 3-point Correlation Function
Abstract
We present the 3-point function 3 and Q3=3/22 for a spectroscopic sample of luminous red galaxies (LRG) from SDSS DR6 & DR7. We find a strong (S/N>6) detection of Q3 on scales of 55-125 Mpc/h, with a well defined peak around 105 Mpc/h in all 2, 3 and Q3, in excellent agreement with the predicted shape and location of the imprint of the baryon acoustic oscillations (BAO). We use very large simulations to asses and test the significance of our measurement. Models without the BAO peak are ruled out by the Q3 data with 99% confidence. Our measurements show the expected shape for Q3 as a function of the triangular configuration. This provides a first direct measurement of the non-linear mode coupling coefficients of density and velocity fluctuations which, on these large scales, are independent of cosmic time, the amplitude of fluctuations or cosmological parameters. The location of the BAO peak in the data indicates m =0.28 0.05 and B=0.079 0.025 (h=0.70) after marginalization over spectral index (ns=0.8-1.2) linear b1 and quadratic c2 bias,which are found to be in the range: b1=1.7-2.2 and c2=0.75-3.55. The data allows a hierarchical contribution from primordial non-Gaussianities in the range Q3=0.55-3.35. These constraints are independent and complementary to the ones that can be obtained using the 2-point function, which are presented in a separate paper. This is the first detection of the shape of Q3 on BAO scales, but our errors are shot-noise dominated and the SDSS volume is still relatively small, so there is ample room for future improvement in this type of measurements.