Modeling and measuring the anisotropic halo 3-point correlation function: a coordinated study

TL;DR

This study develops a model and estimator for the anisotropic 3-point correlation function in galaxy surveys, demonstrating its potential to improve cosmological parameter constraints, though current models have limitations.

Contribution

The paper introduces a novel, efficient model and estimator for the anisotropic 3PCF and evaluates its performance against simulations and mocks.

Findings

Adding anisotropic 3PCF reduces uncertainties in growth rate and AP parameters.

Joint 2PCF+3PCF analysis tightens constraints and breaks degeneracies.

Current models fail to capture small-scale anisotropic information, limiting benefits.

Abstract

Ongoing and future spectroscopic galaxy surveys will cover unprecedented volumes with a number of objects large enough to effectively probe clustering anisotropies through higher-order statistics. In this work, we present a novel and efficient implementation of both a model for the multipole moments of the anisotropic 3-point correlation function (3PCF) and of their estimator. To evaluate the performance of our model, we compared its predictions against direct 3PCF measurements obtained with our estimator from a set of 298 dark matter halo catalogs drawn from the $z=1$ snapshots of $N$-body simulations. For the statistical analysis, we employed a covariance matrix estimated from an independent suite of 3000 mock halo catalogs at the same redshift. We then repeated the analysis by combining the 2-point correlation function (2PCF) to the 3PCF, with and without including its anisotropic part. In the 3PCF-only analysis, the addition of the anisotropic component of the 3PCF effectively breaks the degeneracy between the growth rate $f$ and the linear bias $b_1$, significantly reducing their uncertainties. It also significantly improves the precision of the Alcock-Paczynski parameter $\varepsilon$ but does not reduce the $\sim 1$% offset we find in the estimate of the isotropic dilation parameter $\alpha$. The joint 2PCF+3PCF analysis reduces, though does not fully remove, biases in the AP and isotropic dilation parameters and breaks the $f$-$b_1$-$\sigma_8$ degeneracy, leading to tighter constraints overall. The anisotropic 3PCF adds little to the joint analysis because the tree-level 3PCF model fails to capture the anisotropic information primarily encoded on small scales and in squeezed triangle configurations. A more advanced model will be required to exploit this information fully.