Acknowledgements

RG and VS acknowledge support by the DFG Research Centre SFB-881 `The Milky Way System' through project A1. This work has also been supported by the European Research Council under ERC-StG grant EXAGAL- 308037.

The Auriga project is a flagship project of the Virgo Consortium. The Auriga simulations were run on the SuperMUC system at the Leibniz Computing Centre, Garching, under the project PR85JE of the Gauss Centre for Supercomputing, and the Magny computer cluster at the Heidelberg Institute for Theoretical studies (HITS). This work used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility `www.dirac.ac.uk'. This equipment was funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/H008519/1, and STFC DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the UK National E-Infrastructure.