Priors on red galaxy stochasticity from hybrid effective field theory

TL;DR

This paper uses hybrid effective field theory and halo occupation distribution modeling to analyze the stochastic properties of red galaxy samples, providing priors for cosmological analyses and connecting different galaxy-halo modeling frameworks.

Contribution

It introduces a novel application of hybrid EFT to characterize galaxy-halo connection models at the field level, revealing stochasticity behaviors and establishing priors for future cosmological studies.

Findings

Galaxy samples show stochasticity from sub-Poisson to super-Poisson.

Halo host haloes exhibit sub-Poisson stochasticity.

Methodology links hybrid EFT with galaxy-halo connection modeling.

Abstract

We investigate the stochastic properties of typical red galaxy samples in a controlled numerical environment. We use Halo Occupation Distribution (HOD) modelling to create mock realizations of three separate bright red galaxy samples consistent with datasets used for clustering and lensing analyses in modern galaxy surveys. Second-order Hybrid Effective Field Theory (HEFT) is used as a field-level forward model to describe the full statistical distribution of these tracer samples, and their stochastic power spectra are directly measured and compared to the Poisson shot-noise prediction. While all of the galaxy samples we consider are hosted within haloes with sub-Poisson stochasticity, we observe that the galaxy samples themselves possess stochasticities that range from sub-Poisson to super-Poisson, in agreement with predictions from the halo model. As an application of our methodology, we place priors on the expected degree of non-Poisson stochasticity in cosmological analyses using such samples. We expect these priors will be useful in reducing the complexity of the full parameter space for future analyses using second-order Lagrangian bias models. More generally, the techniques outlined here present the first application of hybrid EFT methods to characterize models of the galaxy--halo connection at the field level, revealing new connections between once-disparate modelling frameworks.