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NIHAO – XI. Formation of ultra-diffuse galaxies by outflows

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 L ⋆ galaxies or diffuse dwarfs, are challenging issues. Using zoom-in cosmologic...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society. Letters 2017-03, Vol.466 (1), p.L1-L6
Main Authors: Di Cintio, Arianna, Brook, Chris B., Dutton, Aaron A., Macciò, Andrea V., Obreja, Aura, Dekel, Avishai
Format: Article
Language:English
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Summary: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 L ⋆ galaxies or diffuse dwarfs, are challenging issues. Using zoom-in cosmological simulations from the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project, we show that UDG analogues form naturally in dwarf-sized haloes due to episodes of gas outflows associated with star formation. The simulated UDGs live in isolated haloes of masses 1010–11 M⊙, have stellar masses of 107–8.5 M⊙, effective radii larger than 1 kpc and dark matter cores. They show a broad range of colours, an average Sérsic index of 0.83, a typical distribution of halo spin and concentration, and a non-negligible H i gas mass of 107 − 9 M⊙, which correlates with the extent of the galaxy. Gas availability is crucial to the internal processes which 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 H i gas than less extended dwarfs of similar M ⋆.
ISSN:1745-3925
1745-3933
DOI:10.1093/mnrasl/slw210