The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time

TL;DR

This study uses advanced cosmological simulations to explore how galaxy disc sizes and properties are influenced by angular momentum, mergers, and feedback processes across cosmic time.

Contribution

It introduces a new suite of magneto-hydrodynamical simulations that realistically model galaxy formation, revealing key mechanisms behind disc galaxy properties.

Findings

Large discs result from quiescent mergers depositing high angular momentum.

Violent mergers and AGN feedback limit disc size and suppress star formation.

Low halo angular momentum leads to compact discs and bulge formation.

Abstract

We introduce a suite of thirty cosmological magneto-hydrodynamical zoom simulations of the formation of galaxies in isolated Milky Way mass dark haloes. These were carried out with the moving mesh code \textlcsc{AREPO}, together with a comprehensive model for galaxy formation physics, including AGN feedback and magnetic fields, which produces realistic galaxy populations in large cosmological simulations. We demonstrate that our simulations reproduce a wide range of present-day observables, in particular, two component disc dominated galaxies with appropriate stellar masses, sizes, rotation curves, star formation rates and metallicities. We investigate the driving mechanisms that set present-day disc sizes/scale lengths, and find that they are related to the angular momentum of halo material. We show that the largest discs are produced by quiescent mergers that inspiral into the galaxy and deposit high angular momentum material into the pre-existing disc, simultaneously increasing the spin of dark matter and gas in the halo. More violent mergers and strong AGN feedback play roles in limiting disc size by destroying pre-existing discs and by suppressing gas accretion onto the outer disc, respectively. The most important factor that leads to compact discs, however, is simply a low angular momentum for the halo. In these cases, AGN feedback plays an important role in limiting central star formation and the formation of a massive bulge.