Baryonic effects on the matter bispectrum

TL;DR

This paper investigates how baryonic physics, especially AGN feedback, affects the matter bispectrum using hydrodynamical simulations, revealing a low-redshift enhancement that could aid in breaking degeneracies in cosmological measurements.

Contribution

It provides the first detailed analysis of baryonic effects on the matter bispectrum across multiple simulations and offers publicly available measurements and tools for further research.

Findings

Identification of a low-redshift bispectrum enhancement peaking at $k\,\sim\,3h\,\mathrm{Mpc}^{-1}$

The enhancement is linked to evolving AGN feedback at late times

The bispectrum enhancement offers a new way to break degeneracies in cosmological analyses

Abstract

The large-scale clustering of matter is impacted by baryonic physics, particularly AGN feedback. Modelling or mitigating this impact will be essential for making full use of upcoming measurements of cosmic shear and other large-scale structure probes. We study baryonic effects on the matter bispectrum, using measurements from a selection of state-of-the-art hydrodynamical simulations: IllustrisTNG, Illustris, EAGLE, and BAHAMAS. We identify a low-redshift enhancement of the bispectrum, peaking at $k\sim 3h\,{\rm Mpc}^{-1}$, that is present in several simulations, and discuss how it can be associated to the evolving nature of AGN feedback at late times. This enhancement does not appear in the matter power spectrum, and therefore represents a new source of degeneracy breaking between two- and three-point statistics. In addition, we provide physical interpretations for other aspects of these measurements, and make initial comparisons to predictions from perturbation theory, empirical fitting formulas, and the response function formalism. We publicly release our measurements (including estimates of their uncertainty due to sample variance) and bispectrum measurement code as resources for the community.