The recurrent impact of the Sagittarius dwarf on the Milky Way star
  formation history
  Satellites orbiting disc galaxies can induce phase space features such as
spirality, vertical heating and phase-mixing in their discs. Such features have
also been observed in our own Galaxy, but the complexity of the Milky Way disc
has only recently been fully mapped thanks to Gaia DR2 data. This complex
behaviour is mainly ascribed to repeated perturbations induced by the
Sagittarius dwarf galaxy (Sgr) along its orbit, pointing to this satellite as
the main dynamical architect of the Milky Way disc. Here, we model Gaia DR2
observed colour-magnitude diagrams to obtain the first detailed star formation
history of the ~ 2-kpc bubble around the Sun. It reveals three conspicuous and
narrow episodes of enhanced star formation that we can precisely date as having
occurred 5.7, 1.9 and 1 Gyr ago. Interestingly, the timing of these episodes
coincides with proposed Sgr pericentre passages according to i) orbit
simulations, ii) phase space features in the Galactic disc, and iii) Sgr
stellar content. These findings most likely suggest that Sgr has also been an
important actor in the build-up of the Milky Way disc stellar mass, with its
perturbations repeatedly triggering major episodes of star formation.
