Calibrating galaxy formation effects in galactic tests of fundamental physics

TL;DR

This paper develops a framework using cosmological simulations to calibrate and assess the reliability of astrophysical noise models in galactic tests of fundamental physics, highlighting the importance of detailed baryonic modeling.

Contribution

It introduces a method to test and improve baryonic noise models in galaxy-based physics tests using hydrodynamical simulations, emphasizing case-by-case analysis.

Findings

Gaussian noise models well describe galaxy warping effects.

Gas-star offsets correlate with host halo virial radius.

Systematic uncertainties of about 30% due to baryonic physics are identified.

Abstract

Galactic scale tests have proven to be powerful tools in constraining fundamental physics in previously under-explored regions of parameter space. The astrophysical regime which they probe is inherently complicated, and the inference methods used to make these constraints should be robust to baryonic effects. Previous analyses have assumed simple empirical models for astrophysical noise without detailed calibration or justification. We outline a framework for assessing the reliability of such methods by constructing and testing more advanced baryonic models using cosmological hydrodynamical simulations. As a case study, we use the Horizon-AGN simulation to investigate warping of stellar disks and offsets between gas and stars within galaxies, which are powerful probes of screened fifth forces. We show that the degree of `U'-shaped warping of galaxies is well modelled by Gaussian random noise, but that the magnitude of the gas-star offset is correlated with the virial radius of the host halo. By incorporating this correlation we confirm recent results ruling out astrophysically relevant Hu-Sawicki $f(R)$ gravity, and identify a $\sim 30\%$ systematic uncertainty due to baryonic physics. Such an analysis must be performed case-by-case for future galactic tests of fundamental physics.