Speaker
Description
Ultra-faint dwarf galaxies (UFDs) are often found in large numbers in close proximity to the Milky Way and other massive spiral galaxies. As such, their projected stellar ellipticity and extended light distributions are often thought to owe to tidal forces. I discuss the projected stellar ellipticities and faint stellar outskirts of isolated ultra-faints, drawn from the `Engineering Dwarfs at Galaxy Formation’s Edge’ (EDGE) cosmological simulation suite. I find that, in spite of their tidal isolation, the simulated dwarfs exhibit a wide range of projected ellipticities ($0.03 < \varepsilon < 0.75$), and show a strong correlation between their ellipticity and formation time. Furthermore, many have anisotropic extended stellar outskirts (the furthest in EDGE being out to 143 half light radii) that can masquerade as tidal tails but are actually due to mergers. I show that the distribution of projected ellipticities in the sample of simulated EDGE dwarfs matches very well that of 22 tidally isolated Local Group dwarf galaxies. These results imply that a significant number of UFDs found to date are tidally isolated, as further suggested by their large orbital peri and apocentres. We argue that this tidal isolation makes nearby UFDs excellent natural laboratories for testing galaxy formation and dark matter models.
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