Hydrodynamical simulations of the galaxy population: enduring successes and outstanding challenges

TL;DR

Hydrodynamical galaxy simulations have achieved significant success in reproducing observed galaxy properties, but challenges remain in modeling circumgalactic gas and feedback processes, which are crucial for understanding galaxy evolution.

Contribution

This review highlights the progress, successes, and challenges in hydrodynamical galaxy simulations, emphasizing the role of feedback models and the importance of CGM observations.

Findings

Simulations can reproduce galaxy properties by calibrating feedback parameters.

Feedback processes differ between low and high mass galaxies, dominated by stars and black holes.

CGM observations are key to resolving degeneracies in feedback models.

Abstract

We review the progress in modelling the galaxy population in hydrodynamical simulations of the Lambda-CDM cosmogony. State-of-the-art simulations now broadly reproduce the observed spatial clustering of galaxies, the distributions of key characteristics such as mass, size and star formation rate, and scaling relations connecting diverse properties to mass. Such improvements engender confidence in the insight drawn from simulations. Many important outcomes however, particularly the properties of circumgalactic gas, are sensitive to the details of the subgrid models used to approximate the macroscopic effects of unresolved physics, such as feedback processes. We compare the outcomes of leading simulation suites with observations and with each other, to identify the enduring successes they have cultivated and the outstanding challenges to be tackled with the next generation of models. Our key conclusions are: 1) Realistic galaxies can be reproduced by calibrating the ill-constrained parameters of subgrid feedback models. Feedback is dominated by stars and by black holes in low mass and high mass galaxies, respectively; 2) Adjusting or disabling the physical processes implemented in simulations can elucidate their impact on observables, but outcomes can be degenerate; 3) Similar galaxy populations can emerge in simulations with dissimilar subgrid feedback implementations. However, these models generally predict markedly different gas flow rates into, and out of, galaxies and their haloes. CGM observations are thus a promising means of breaking this degeneracy and guiding the development of new feedback models.