The Large-Scale 3-point correlation function of SDSS Luminous Red Galaxies

TL;DR

This paper measures the three-point correlation function of SDSS Luminous Red Galaxies on large scales, using the largest dataset to date, to understand galaxy bias and infer cosmological parameters.

Contribution

It provides the first large-scale 3PCF measurements for SDSS LRGs with improved binning, and uses these to estimate galaxy bias and cosmological parameters.

Findings

LRGs are highly biased tracers with linear bias ~2

Large positive non-linear bias consistent with galaxy models

3PCF helps estimate  and halo occupation parameters

Abstract

We present new measurements of the redshift-space three-point correlation function (3PCF) of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS). Using the largest dataset to date, the Data Release 7 (DR7) LRGs, and an improved binning scheme compared to previous measurements, we measure the LRG 3PCF on large scales up to ~90 Mpc/h, from the mildly non-linear to quasi-linear regimes. Comparing the LRG correlations to the dark matter two- and three-point correlation functions, obtained from N-body simulations we infer linear and non-linear bias parameters. As expected, LRGs are highly biased tracers of large scale structure, with a linear bias b1 ~ 2; the LRGs also have a large positive non-linear bias parameter, in agreement with predictions of galaxy population models. The use of the 3PCF to estimate biasing helps to also make estimates of the cosmological parameter {\sigma_8}, as well as to infer best-fit parameters of the Halo Occupation Distribution parameters for LRGs. We also use a large suite of public mock catalogs to characterize the error covariance matrix for the 3PCF and compare the variance among simulation results with jackknife error estimates.