A Sagittarius-like simulated dwarf spheroidal galaxy from TNG50

TL;DR

This paper uses the TNG50 simulation to show how a disky galaxy can evolve into a Sagittarius-like dwarf spheroidal galaxy through tidal interactions with the Milky Way, reproducing observed features.

Contribution

It presents a cosmological simulation-based model demonstrating the formation of a Sagittarius-like dwarf galaxy from a disky progenitor via tidal evolution.

Findings

The simulated dwarf develops a bar-like shape after pericenter passages.

Mass loss leads to a final mass below 10^9 solar masses.

The metallicity gradient and rotation properties match observations.

Abstract

The Sagittarius dwarf spheroidal (Sgr dSph) galaxy provides one of the most convincing examples of tidal interaction between satellite galaxies and the Milky Way (MW). The main body of the dwarf was recently demonstrated to have an elongated, prolate, bar-like shape and to possess some internal rotation. Whether these features are temporary results of the strong tidal interaction at the recent pericenter passage or are due to a disky progenitor is a matter of debate. I present an analog of Sgr selected among bar-like galaxies from the TNG50 simulation of the IllustrisTNG project. The simulated dwarf is initially a disky galaxy with mass exceeding $10^{11}$ M$_\odot$ and evolves around a MW-like host on a tight orbit with seven pericenter passages and a period of about 1 Gyr. At the second pericenter passage, the disk transforms into a bar and the bar-like shape of the stellar component is preserved until the end of the evolution. The morphological transformation is accompanied by strong mass loss, leaving a dwarf with a final mass of below $10^{9}$ M$_\odot$. The gas is lost completely and the star formation ceases at the third pericenter passage. At the last pericenters, the dwarf possesses a bar-like shape, a little remnant rotation, and the metallicity gradient, which are consistent with observations. The more concentrated metal-rich stellar population rotates faster and has a lower velocity dispersion than the more extended metal-poor one. The metallicity distribution evolves so that the most metal-poor stars are stripped first, which explains the metallicity gradient detected in the Sgr stream. This study demonstrates that a dSph galaxy with properties akin to the Sgr dwarf can form from a disky progenitor with a mass of above $10^{11}$ M$_\odot$ by tidal evolution around the MW in the cosmological context.