Galaxy alignments: Theory, modelling and simulations

TL;DR

This review discusses the current theories, models, and simulations of intrinsic galaxy alignments, emphasizing their importance in understanding galaxy formation and the challenges faced in modeling these alignments.

Contribution

It provides a comprehensive overview of theoretical models and simulation efforts for intrinsic galaxy alignments, highlighting recent developments and future directions.

Findings

Intrinsic alignments depend on galaxy type and environment.

Recent simulations are improving understanding of galaxy shape and angular momentum alignments.

The field is still developing with many open questions.

Abstract

The shapes of galaxies are not randomly oriented on the sky. During the galaxy formation and evolution process, environment has a strong influence, as tidal gravitational fields in the large-scale structure tend to align nearby galaxies. Additionally, events such as galaxy mergers affect the relative alignments of both the shapes and angular momenta of galaxies throughout their history. These "intrinsic galaxy alignments" are known to exist, but are still poorly understood. This review will offer a pedagogical introduction to the current theories that describe intrinsic galaxy alignments, including the apparent difference in intrinsic alignment between early- and late-type galaxies and the latest efforts to model them analytically. It will then describe the ongoing efforts to simulate intrinsic alignments using both N-body and hydrodynamic simulations. Due to the relative youth of this field, there is still much to be done to understand intrinsic galaxy alignments and this review summarises the current state of the field, providing a solid basis for future work.