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- Orkney, Matthew D.A., et al.
(författare)
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EDGE : the puzzling ellipticity of Eridanus II's star cluster and its implications for dark matter at the heart of an ultra-faint dwarf
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 515:1, s. 185-200
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Tidskriftsartikel (refereegranskat)abstract
- The Eridanus II (EriII) 'ultra-faint' dwarf has a large (15 pc) and low-mass (4.3 × 103 M·) star cluster (SC) offset from its centre by 23 ± 3 pc in projection. Its size and offset are naturally explained if EriII has a central dark matter core, but such a core may be challenging to explain in a ΛCDM cosmology. In this paper, we revisit the survival and evolution of EriII's SC, focusing for the first time on its puzzlingly large ellipticity (0.31+0.05-0.06). We perform a suite of 960 direct N-body simulations of SCs, orbiting within a range of spherical background potentials fit to ultra-faint dwarf (UFD) galaxy simulations. We find only two scenarios that come close to explaining EriII's SC. In the first scenario, EriII has a low-density dark matter core (of size ∼70 pc and density ≲ 2× 108, M⊙ , kpc-3). In this model, the high ellipticity of EriII's SC is set at birth, with the lack of tidal forces in the core allowing its ellipticity to remain frozen for long times. In the second scenario, EriII's SC orbits in a partial core, with its high ellipticity owing to its imminent tidal destruction. However, this latter model struggles to reproduce the large size of EriII's SC, and it predicts substantial tidal tails around EriII's SC that should have already been seen in the data. This leads us to favour the cored model. We discuss potential caveats to these findings, and the implications of the cored model for galaxy formation and the nature of dark matter.
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| 2. |
- Rey, Martin P., et al.
(författare)
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EDGE : What shapes the relationship between H i and stellar observables in faint dwarf galaxies?
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 511:4, s. 5672-5681
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Tidskriftsartikel (refereegranskat)abstract
- We show how the interplay between feedback and mass-growth histories introduces scatter in the relationship between stellar and neutral gas properties of field faint dwarf galaxies (M∗ 106, M⊙). Across a suite of cosmological, high-resolution zoomed simulations, we find that dwarf galaxies of stellar masses 105 ≤ M∗ ≤ 106, M⊙ are bimodal in their cold gas content, being either H i-rich or H i-deficient. This bimodality is generated through the coupling between (i) the modulation of H i contents by the background of ultraviolet radiation (UVB) at late times and (ii) the significant scatter in the stellar-to-halo mass relationship induced by reionization. Furthermore, our H i-rich dwarfs exhibit disturbed and time-variable neutral gas distributions primarily due to stellar feedback. Over the last four billion years, we observe order-of-magnitude changes around the median M H,\small I, factor-of-a-few variations in H i spatial extents, and spatial offsets between H i and stellar components regularly exceeding the galaxies' optical sizes. Time variability introduces further scatter in the M∗-M H, small I relation and affects a galaxy's detectability in H i at any given time. These effects will need to be accounted for when interpreting observations of the population of faint, H i-bearing dwarfs by the combination of optical and radio wide, deep surveys.
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