  The scientific exploitation of the Dark Energy Spectroscopic Instrument
Bright Galaxy Survey (DESI BGS) data requires the construction of mocks with
galaxy population properties closely mimicking those of the actual DESI BGS
targets. We create a high fidelity mock galaxy catalogue, including information
about galaxies and their host dark matter subhaloes. The mock catalogue uses
subhalo abundance matching (SHAM) with scatter to populate the P-Millennium
N-body simulation with galaxies at the median BGS redshift of ~ 0.2, using
formation redshift information to assign (g-r) rest-frame colours. The mock
provides information about r-band absolute magnitudes, (g-r) rest-frame
colours, 3D positions and velocities of a complete sample of DESI BGS galaxies
in a volume of (542 Mpc/h)^3, as well as the masses of host dark matter haloes.
This P-Millennium DESI BGS mock catalogue is ideally suited for the tuning of
approximate mocks unable to resolve subhaloes that DESI BGS galaxies reside in,
to test for systematics in analysis pipelines and to interpret
(non-cosmological focused) DESI BGS analysis.

Cosmology and Nongalactic Astrophysics