The BAHAMAS project: Calibrated hydrodynamical simulations for large-scale structure cosmology

TL;DR

The BAHAMAS project develops calibrated hydrodynamical simulations that accurately model the distribution of matter and galaxy properties, reducing uncertainties in large-scale structure cosmology.

Contribution

This work introduces a new suite of large-volume simulations with feedback models calibrated to observations, improving the predictive power for cosmological studies.

Findings

Simulations reproduce observed galaxy stellar mass functions.

Accurately match hot gas fractions in groups and clusters.

Capture the relationships between galaxies, gas, and dark matter.

Abstract

The evolution of the large-scale distribution of matter is sensitive to a variety of fundamental parameters that characterise the dark matter, dark energy, and other aspects of our cosmological framework. Since the majority of the mass density is in the form of dark matter that cannot be directly observed, to do cosmology with large-scale structure one must use observable (baryonic) quantities that trace the underlying matter distribution in a (hopefully) predictable way. However, recent numerical studies have demonstrated that the mapping between observable and total mass, as well as the total mass itself, are sensitive to unresolved feedback processes associated with galaxy formation, motivating explicit calibration of the feedback efficiencies. Here we construct a new suite of large-volume cosmological hydrodynamical simulations (called BAHAMAS, for BAryons and HAloes of MAssive Systems) where subgrid models of stellar and Active Galactic Nucleus (AGN) feedback have been calibrated to reproduce the present-day galaxy stellar mass function and the hot gas mass fractions of groups and clusters in order to ensure the effects of feedback on the overall matter distribution are broadly correct. We show that the calibrated simulations reproduce an unprecedentedly wide range of properties of massive systems, including the various observed mappings between galaxies, hot gas, total mass, and black holes, and represent a significant advance in our ability to mitigate the primary systematic uncertainty in most present large-scale structure tests.