Maarten A. Breddels, A. Helmi, R. C. E. van den Bosch, G. van de Ven, G. Battaglia
We have developed spherically symmetric dynamical models of dwarf spheroidal galaxies using Schwarzschild's orbit superposition method. This type of modelling yields constraints both on the total mass distribution (e.g. enclosed mass and scale radius) as well as on the orbital structure of the system (e.g. velocity anisotropy). This method is thus less prone to biases introduced by assumptions in comparison to the more commonly used Jeans modelling, and it allows us to derive the dark matter content in a robust way. Here we present our results for the Sculptor dwarf spheroidal galaxy, after testing our methods on mock data sets. We fit both the second and fourth velocity moment profile to break the mass-anisotropy degeneracy. We find that the mass of Sculptor within 1 kpc is M_1kpc = (1.03 \pm 0.07) \times 10^8 M\odot, and that its velocity anisotropy profile is tangentially biased and nearly constant with radius. For an NFW dark matter profile, the preferred concentration (c \sim 15) is low for its dark matter mass but consistent within the scatter found in N-body cosmological simulations. Very cuspy density profiles with logarithmic central slopes {\alpha} < -1.5 are strongly disfavoured for Sculptor. However, a firm distinction between a central core ({\alpha} = 0) or a shallower cusp ({\alpha} >=-1) cannot be made.
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http://arxiv.org/abs/1205.4712
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