2.1 Introduction

Author(s): Carine Babusiaux

Simulations have been needed for the mission design and the DPAC algorithms training and tests. They are currently used within DPAC mainly for the catalogue validation and they are used by the community to exploit the Gaia data or to prepare spectroscopic follow-ups.

Three different levels of simulations have been made available within DPAC:

• •

  pixel-level simulations from the Gaia Instrument and Basic Image Simulator (GIBIS; Babusiaux et al. 2011)

• •

  telemetry simulations from the GAia System level Simulator (GASS; Masana et al. 2008)

• •

  DPAC object products from the Gaia Object Generator (GOG; Luri et al. 2014)

As a by product of GOG catalogues, we produce Gaia Universe Model Snapshot catalogues (GUMS; Robin et al. 2012), which corresponds to the intrinsic properties of the objects generated by GOG before applying the Gaia instrument modelling and DPAC processing simulation.

GUMS 10, described in (Robin et al. 2012) is available at VizieR. GUMS and GOG 18 have been made available in HDF5 format and TAP access in Paris Observatory. Within Gaia EDR3, we release galactic stars generated with GUMS and GOG 20. GUMS can be found in the auxiliary table gaia_universe_model and GOG in the auxiliary table gaia_source_simulation. We describe here the GUMS model in Section 2.2 and the GOG simulator in Section 2.3.