Impact of orbiting satellites on star formation rate evolution and metallicity variations in Milky Way-like discs

Abstract

At least one major merger is currently taking place in the MW. The Sgr dwarf spheroidal galaxy is being tidally destroyed while orbiting around the MW, whose close passages perturb the MW disc externally. In this work, using a series of hydrodynamical simulations, we investigate how massive dwarf galaxies on quasi-polar Sgr-like orbits impact the star formation activity inside the MW-like discs. First, we confirm that interactions with orbiting satellites enhance the star formation rate in the host galaxy. However, prominent short-time scale bursts are detected during the very close passages ($<20$ kpc) of massive ($>2\times 10^{10} M_\odot$) gas-poor satellites. In the case of gas-rich satellites, while we see a substantial enhancement of the star formation on a longer time scale, we do not detect prominent peaks in the star formation history of the host. This can be explained by the steady accretion of gas being stripped from the satellite, which smoothens short-term variations in the star formation rate of the host. It is important that the impact of the satellite perturbations, especially its first encounters, is seen mainly in the outer~($>10$ kpc) disc of the host. We also found that the close passages of satellites cause the formation of a substantial amount of low-metallicity stars in the host, and the effect is the most prominent in the case of gas infall from the satellites resulting in the dilution of the mean stellar metallicity soon after the first pericentric passage of massive satellites. Our simulations are in favour of causality between the recent passages of the Sgr galaxy and the bursts of the star formation in the solar neighbourhood~($\approx 1$ and $\approx 2$ Gyr ago); however, in order to reproduce the SF burst at its first infall ($\approx 6$ Gyr), we require a very close pericentric passage ($<20$ kpc) with subsequent substantial mass loss of the Sgr precursor.