paper

NIHAO XI: Formation of Ultra-Diffuse Galaxies by outflows

arXiv:1608.01327 · doi:10.1093/mnrasl/slw210

Abstract

We address the origin of Ultra-Diffuse Galaxies (UDGs), which have stellar masses typical of dwarf galaxies but effective radii of Milky Way-sized objects. Their formation mechanism, and whether they are failed galaxies or diffuse dwarfs, are challenging issues. Using zoom-in cosmological simulations from the NIHAO project, we show that UDG analogues form naturally in medium-mass haloes due to episodes of gas outflows associated with star formation. The simulated UDGs live in isolated haloes of masses , have stellar masses of , effective radii larger than 1 kpc and dark matter cores. They show a broad range of colors, an average Sérsic index of 0.83, a typical distribution of halo spin and concentration, and a non-negligible HI gas mass of , which correlates with the extent of the galaxy. Gas availability is crucial to the internal processes that form UDGs: feedback driven gas outflows, and subsequent dark matter and stellar expansion, are the key to reproduce faint, yet unusually extended, galaxies. This scenario implies that UDGs represent a dwarf population of low surface brightness galaxies and should exist in the field. The largest isolated UDGs should contain more HI gas than less extended dwarfs of similar .

arXiv commentmatches accepted version, MNRAS Letter 2016-10-12

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