Clustering of luminous red galaxies - III. Baryon acoustic peak in the three-point correlation

Abstract

We present the three-point function ξ3 and Q3 = ξ3ξ22 for a spectroscopic sample of luminous red galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 6 and Data Release 7. We find a strong (signal-to-noise ratio > 6) detection of Q3 on scales of 55-125 Mpch, with a well-defined peak around 105 Mpch in all ξ2, ξ3 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 (from a cubic box of L = 7680 Mpch) to assess and test the significance of our measurement. Models without the BAO peak are ruled out by the Q3 data with 99 per cent confidence. This detection demonstrates the non-linear growth of structure by gravitational instability between z = 1000 and the present. 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 Ωm = 0.28 ± 0.05 and ΩB = 0.079 ± 0.025 (for h = 0.70) after marginalization over spectral index (n s = 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 allow 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 two-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. © 2009 RAS.