Aurigaia: mock Gaia DR2 stellar catalogues from the auriga cosmological simulations

We present and analyse mock stellar catalogues that match the selection criteria and observ-ables (including uncertainties) of the Gaia satellite data release 2 (DR2). The source are six cosmological high-resolution magneto-hydrodynamic ACDM zoom simulations of the formation of Milky Way analogues from the AURIGA project. Mock data are provided for stars with V < 16 mag and V < 20 mag at vertical bar b vertical bar > 20 deg. The mock catalogues are made using two different methods: the public SNAPDRAGONS code, and a method based on that of Lowing et al. (2015) that preserves the phase-space distribution of the model stars. These publicly available catalogues contain five-parameter astrometry, radial velocities, multiband photometry, stellar parameters, dust extinction values, and uncertainties in all these quantities. In addition, we provide the gravitational potential and information on the origin of each star. By way of demonstration, we apply the mock catalogues to analyses of the young stellar disc and the stellar halo. We show that (i) the young outer stellar disc exhibits a flared distribution that is detectable in the height and vertical velocity distribution of A- and B-dwarf stars up to radii of similar to 15 kpc, and (ii) the spin of the stellar halo out to 100 kpc can be accurately measured with Gala DR2 RR Lyrae stars. These catalogues are well suited for comparisons with observations and should help to (i) develop and test analysis methods for the Gaia DR2 data, (ii) gauge the limitations and biases of the data, and (iii) interpret the data in the light of theoretical predictions from realistic ab initio simulations of galaxy formation in the ACDM cosmological model.