2024MNRAS.527.2426A

At least one major merger is currently taking place in the Milky Way (MW). The Sagittarius (Sgr) dwarf galaxy is being tidally destroyed while orbiting around the MW, whose close passages perturb the disc externally. In this work, using hydrodynamical simulations, we investigate how massive dwarf galaxies on quasi-polar Sgr-like orbits impact the star formation (SF) inside the MW-like discs. First, we confirm that interactions with orbiting satellites enhance the SF rate in the host. However, prominent SF bursts are detected during the very close passages (<20 kpc) of massive (2 × 10¹⁰ M_⊙) gas-poor satellites. For gas-rich satellites, while we observe substantial enhancement of the SF, we do not detect prominent peaks in the SF history of the host. This can be explained by the steady gas accretion from the satellite smoothening short-term variations in the SF. The impact of the satellite perturbations, especially its first encounters, is seen mainly in the outer (>10 kpc) disc. We also found that the close passages of satellites cause the formation of low-metallicity stars in the host, and the effect is the most prominent for gas infall from the satellites resulting in the dilution of the mean stellar metallicity. Our simulations are in favour of causality between the recent passages of the Sgr and the bursts of the SF in the solar neighbourhood (≈1 and ≈2 Gyr ago); however, to reproduce the SF burst at its first infall (≈6 Gyr), we require a very close passage (<20 kpc) with subsequent substantial mass-loss of the Sgr precursor.