Fossil stellar streams and their globular cluster populations in the E-MOSAICS simulations

TL;DR

This study uses the E-MOSAICS simulations to analyze globular clusters in stellar streams, revealing how their properties relate to the accretion history of galaxies and providing methods to estimate galaxy infall times.

Contribution

It demonstrates how globular cluster characteristics can be used to infer the mass and infall time of accreted galaxies in stellar streams, based on hydrodynamical simulations.

Findings

More massive accreted galaxies host younger, more metal-rich GCs.

Later accreted galaxies have younger GCs due to extended formation periods.

Estimated infall time of Sagittarius dwarf galaxy is approximately 9.3 Gyr.

Abstract

Stellar haloes encode a fossil record of a galaxy's accretion history, generally in the form of structures of low surface brightness, such as stellar streams. While their low surface brightness makes it challenging to determine their age, metallicity, kinematics and spatial structure, the infalling galaxies also deposit globular clusters (GCs) in the halo, which are bright and therefore easier to observe and characterise. To understand how GCs associated with stellar streams can be used to estimate the stellar mass and the infall time of their parent galaxy, we examine a subset of 15 simulations of galaxies and their star clusters from the E-MOSAICS project. E-MOSAICS is a suite of hydrodynamical simulations incorporating a sub-grid model for GC formation and evolution. We find that more massive accreted galaxies typically contribute younger and more metal rich GCs. This lower age results from a more extended cluster formation history in more massive galaxies. In addition, at fixed stellar mass, galaxies that are accreted later host younger clusters, because they can continue to form GCs without being subjected to environmental influences for longer. This explains the large range of ages observed for clusters associated with the Sagittarius dwarf galaxy in the halo of the Milky Way compared to clusters which are thought to have formed in satellites accreted early in the Milky Way's formation history. Using the ages of the GCs associated with the Sagittarius dwarf, we estimate a virial radius crossing lookback time (infall time) of $9.3 \pm 1.8 Gyr$.