IAUS379: Dynamical Masses of Local Group Galaxies

The mass-anisotropy degeneracy is still one of the main issues in estimating the dark matter distribution in dwarf spheroidal galaxies, especially for the commonly used second-order Jeans analysis. We study the extension of spherical Jeans modeling by incorporating the fourth-order velocity moments under the assumption of dynamical equilibrium and a constant velocity anisotropy. The inclusion of fourth-order velocity moments allows stars’ l.o.s velocity distribution, which is sensitive to the value of the velocity anisotropy parameter, to be flexible, covering thin-tailed to heavy-tailed distributions that is inaccessible if only second-order moments are used. We test our stellar dynamical modeling using mock data that resembles Draco dSph with either central NFW cusp or Burkert core and isotropic velocity anisotropy. Using 500 sample stars, our simulations show that incorporating fourth-order velocity moments improves the results compared to when only second-order moments are used. Typically, the velocity anisotropy is constrained two times better, while it is ~50% improvement for the constraint of the inner dark matter density slope with both parameters being recovered within 1σ uncertainties.