Analogues of the Milky Way-Sagittarius interaction in the TNG50: effect on the Milky Way

TL;DR

This study uses the TNG50 simulation to investigate whether interactions similar to the Sagittarius-Milky Way encounter significantly affect galactic discs, finding minimal impact on star formation and vertical kinematics in most cases.

Contribution

It demonstrates that typical Sagittarius-like interactions in cosmological simulations rarely cause significant changes in galactic disc properties, challenging previous assumptions.

Findings

90% of Sagittarius analogues had no significant effect on star formation or vertical velocities.

Vertical stellar kinematics respond mainly in cold discs and correlate with interaction strength.

Interactions often occur in already disturbed or perturbed discs, affecting star formation only when pre-existing activity is low.

Abstract

The Sagittarius Dwarf Galaxy is undoubtedly being disrupted in the tidal field of the Milky Way. The Milky Way disc is also found to be in a state of disequilibrium. The role of the Sagittarius in driving or contributing to this disequilibrium has been extensively investigated. Most of these studies, however, assume an initially near-equilibrium disc. It was also hypothesized that the passage of Sagittarius could have increased the star-forming activity in the Solar Neighbourhood. We check whether galaxies that have undergone cosmological evolution are affected by interactions analogous to those between the Sagittarius and the Milky Way. We use the high-resolution simulation TNG50 to look for pairs similar to the Milky Way and Sagittarius. We search within redshift z=1-0 for discs from the MW/M31 sample that interacted with a satellite more massive than 10 billion Msun, had a pericenter smaller than 50 kpc, and was on an approximately polar orbit. We exclude cases where, within 1 Gyr of the pericenter, a similar interaction occurred. In 90 percent of cases, a passage of the Sagittarius analogue had no significant effect on either the vertical velocity field of the disc or the star formation history. A response in vertical stellar kinematics can be found mostly in cold discs and mildly correlates with the strength of interactions. For star formation, the studied interactions had an effect only when little to no star formation was ongoing prior to the interaction, often due to previously disturbed star-forming discs, e.g., from AGN activity. Our results indicate that stellar discs in TNG50 are frequently vertically perturbed preceding pericenter passages of Sagittarius analogues. Future studies using other simulations and extragalactic surveys will help establish whether vertical disequilibrium is a common feature of disc galaxies or an artifact of the specific setup studied.