A novel JEAnS analysis of the Fornax dwarf using evolutionary algorithms: mass follows light with signs of an offcentre merger
Abstract
Dwarf galaxies, among the most dark matter dominated structures of our Universe, are excellent testbeds for dark matter theories. Unfortunately, mass modelling of these systems suffers from the welldocumented massvelocity anisotropy degeneracy. For the case of spherically symmetric systems, we describe a method for nonparametric modelling of the radial and tangential velocity moments. The method is a numerical velocity anisotropy 'inversion', with parametric mass models, where the radial velocity dispersion profile, σ_{rr}^{2}, is modelled as a Bspline, and the optimization is a threestep process that consists of (I) an evolutionary modelling to determine the mass model form and the best Bspline basis to represent σ_{rr}^{2}; (II) an optimization of the smoothing parameters and (III) a Markov chain Monte Carlo analysis to determine the physical parameters. The massanisotropy degeneracy is reduced into mass model inference, irrespective of kinematics. We test our method using synthetic data. Our algorithm constructs the best kinematic profile and discriminates between competing dark matter models. We apply our method to the Fornax dwarf spheroidal galaxy. Using a King brightness profile and testing various dark matter mass models, our model inference favours a simple massfollowslight system. We find that the anisotropy profile of Fornax is tangential (β(r) < 0) and we estimate a total mass of M_{tot} = 1.613^{+0.050}_{0.075} × 10^8 M_{⊙}, and a masstolight ratio of Υ_V = 8.93 ^{+0.32}_{0.47} (M_{⊙}/L_{⊙}). The algorithm we present is a robust and computationally inexpensive method for nonparametric modelling of spherical clusters independent of the massanisotropy degeneracy.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 September 2017
 DOI:
 10.1093/mnras/stx1219
 arXiv:
 arXiv:1705.05724
 Bibcode:
 2017MNRAS.470.2034D
 Keywords:

 methods: statistical;
 techniques: radial velocities;
 galaxies: dwarf;
 galaxies: individual: Fornax;
 galaxies: kinematics and dynamics;
 Local Group;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 22 pages, 17 figures, accepted for publication in MNRAS