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

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 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.

Decoding Galactic Merger Histories

“…For this purpose, we use simulations of stellar halos including only accreted stars (e.g., [4,24,46]). For this particular analysis, we used the cosmologically-motivated particle-tagging models of [4], although we found that we recovered similar results with a particle-tagging model with more diverse accretion histories [26] and the accreted particles from two very different hydrodynamical simulations, Auriga and Illustris [9,10,24,31,47]. In these model accreted halos, most of the stellar halo mass lies at less than 10 kpc galactocentric radius.…”

The milky way total mass profile as inferred from Gaia DR2

“…Auriga is a suite of high-resolution magneto-hydrodynamical simulations of MW-mass haloes ran with the AREPO code (Springel 2010). The suite consist of 40 haloes, 30 of which have mass, M200 ∈ [1, 2] × 10 12 M , and were first introduced in Grand et al (2017), plus 10 additional lower mass haloes, with M200 masses just below ∼10 12 M (Grand et al 2019a). The Auriga systems are zoom-in resimulations of MW-mass haloes selected from the EAGLE 100 3 Mpc 3 periodic cube simulation (Schaye et al 2015) that are relatively isolated at z = 0, that is have no objects more massive than half their halo mass within a distance of 1.37 Mpc.…”

“…The Auriga systems are zoom-in resimulations of MW-mass haloes selected from the EAGLE 100 3 Mpc 3 periodic cube simulation (Schaye et al 2015) that are relatively isolated at z = 0, that is have no objects more massive than half their halo mass within a distance of 1.37 Mpc. See Grand et al 2017 for more details, as well as for illustrations and properties of the central galaxies in the Auriga haloes.…”

Dark matter halo shapes in the Auriga simulations

“…The simulations come in two versions: dark matter only and full baryonic physics included (this entails magetohydrodynamics, gas cooling, star formation, black hole growth, and associated feedback processes). A detailed description of the simulations, the numerical treatment, and the resulting galaxy properties can be found in Grand et al (2017). Here we summarize some of the main features.…”