High-resolution three-dimensional simulations of gas removal from ultrafaint dwarf galaxies. I. Stellar feedback

TL;DR

This study uses high-resolution 3D hydrodynamic simulations to investigate if stellar feedback alone can remove gas from ultrafaint dwarf galaxies, finding that most gas remains bound despite supernova energy output.

Contribution

First detailed hydrodynamic simulation showing stellar feedback alone is insufficient to expel gas from ultrafaint dwarf galaxies.

Findings

Most cold gas is retained despite supernova energy.

Metal-enriched ejecta can escape the galaxy.

Galactic outflows do not develop solely from stellar feedback.

Abstract

The faintest Local Group galaxies found lurking in and around the Milky Way halo provide a unique test bed for theories of structure formation and evolution on small scales. Deep Subaru and Hubble Space Telescope photometry demonstrates that their stellar populations are old, and that the star formation activity did not last longer than 2 Gyr in these systems. A few mechanisms that may lead to such a rapid quenching have been investigated by means of hydrodynamic simulations, without providing any final assessment so far. This is the first in a series of papers aimed at analysing the roles of stellar feedback, ram pressure stripping, host-satellite tidal interactions and reionization in cleaning the lowest-mass Milky Way companions of their cold gas, by using high-resolution, three-dimensional hydrodynamic simulations. We simulate an isolated ultrafaint dwarf galaxy loosely modeled after Bootes I, and examine whether or not stellar feedback alone could drive a substantial fraction of the ambient gas out from the shallow potential well. In contrast to simple analytical estimates, but in agreement with previous hydrodynamical studies, we find that most of the cold gas reservoir is retained. Conversely, a significant fraction of the metal-enriched stellar ejecta crosses the boundaries of the computational box with velocities exceeding the local escape velocity and is, thus, likely lost from the system. Although the total energy output from multiple supernova explosions exceeds the binding energy of the gas, no galactic-scale outflow develops in our simulations and as such, most of the ambient medium remains trapped within the weak potential well of the model galaxy. It seems thus unavoidable that, in order to explain the dearth of gas in ultrafaint dwarf galaxies, we will have to resort to environmental effects. This will be the subject of a forthcoming paper.