Does the Fornax dwarf spheroidal have a central cusp or core? |
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| Authors: | Tobias Goerdt Ben Moore J I Read Joachim Stadel Marcel Zemp |
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| Institution: | Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland;Institute of Astronomy, ETH Zürich, ETH Hönggerberg HPF D6, CH-8093 Zürich, Switzerland |
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| Abstract: | The dark matter dominated Fornax dwarf spheroidal has five globular clusters orbiting at ～1 kpc from its centre. In a cuspy cold dark matter halo the globulars would sink to the centre from their current positions within a few Gyr, presenting a puzzle as to why they survive undigested at the present epoch. We show that a solution to this timing problem is to adopt a cored dark matter halo. We use numerical simulations and analytic calculations to show that, under these conditions, the sinking time becomes many Hubble times; the globulars effectively stall at the dark matter core radius. We conclude that the Fornax dwarf spheroidal has a shallow inner density profile with a core radius constrained by the observed positions of its globular clusters. If the phase space density of the core is primordial then it implies a warm dark matter particle and gives an upper limit to its mass of ～0.5 keV, consistent with that required to significantly alleviate the substructure problem. |
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| Keywords: | methods: N-body simulations galaxies: dwarf galaxies: individual: Fornax galaxies: star clusters |
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