The Effect of Environment on Milky Way-mass galaxies in a Constrained Simulation of the Local Group

TL;DR

This study uses constrained simulations to analyze how environment influences star formation, gas content, and morphology of Milky Way-like galaxies, revealing environment's role in star formation enhancement without affecting morphology.

Contribution

First to compare star formation and gas properties of MW-mass galaxies in constrained Local Group simulations with broader environments.

Findings

Higher environmental density correlates with increased star formation rates.

Environment does not significantly influence galaxy morphology.

Richer environments may replenish star-forming gas in MW-like galaxies.

Abstract

In this letter we present, for the first time, a study of star formation rate, gas fraction and galaxy morphology of a constrained simulation of the Milky Way (MW) and Andromeda (M31) galaxies, compared to other MW-mass galaxies. By combining with unconstrained simulations we cover a sufficient volume to compare these galaxies environmental densities ranging from the field to that of the Local Group (LG). This is particularly relevant as it has been shown that, quite generally, galaxy properties depend intimately upon their environment, most prominently when galaxies in clusters are compared to those in the field. For galaxies in loose groups such as the LG, however, environmental effects have been less clear. We consider the galaxy's environmental density in spheres of 1200 kpc (comoving) and find that whilst environment does not appear to directly affect morphology, there is a positive trend with star formation rates. This enhancement in star formation occurs systematically for galaxies in higher density environments, regardless whether they are part of the LG or in filaments. Our simulations suggest that the richer environment at Mpc-scales may help replenish the star-forming gas, allowing higher specific star formation rates in galaxies such as the MW.