Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy
  within a cored, prolate DM halo
  We present multi-tracer dynamical models of the low mass ($M_{*} \sim
10^{7}$), isolated dwarf irregular galaxy WLM in order to simultaneously
constrain the inner slope of the dark matter (DM) halo density profile
($\gamma$) and flattening ($q_\mathrm{DM}$), and the stellar orbital anisotropy
($\beta_{z}, \beta_{r}$). For the first time, we show how jointly constraining
the mass distribution from the HI gas rotation curve and solving the Jeans'
equations with discrete stellar kinematics leads to a factor of $\sim2$
reduction in the uncertainties on $\gamma$. The mass-anisotropy degeneracy is
also partially broken, leading to reductions on uncertainty by $\sim 30\%$ on
$M_\mathrm{vir}$ (and $\sim 70\%$ at the half-light radius) and $\sim 25\%$ on
anisotropy. Our inferred value of $\gamma = 0.3 \pm 0.1$ is robust to the halo
geometry, and in excellent agreement with predictions of stellar feedback
driven DM core creation. The derived prolate geometry of the DM halo with
$q_\mathrm{DM} = 2 \pm 1$ is consistent with $\Lambda$CDM simulations of dwarf
galaxy halos. While self-interacting DM (SIDM) models with $\sigma/m_{X} \sim
0.6$ can reproduce this cored DM profile, the interaction events may
sphericalise the halo. The simultaneously cored and prolate DM halo may
therefore present a challenge for SIDM. Finally we find that the radial profile
of stellar anisotropy in WLM ($\beta_{r}$) follows a nearly identical trend of
increasing tangential anisotropy to the classical dSphs, Fornax and Sculptor.
Given WLM's orbital history, this result may call into question whether such
anisotropy is a consequence of tidal stripping in only one pericentric passage
or if it instead is a feature of the largely self-similar formation and
evolutionary pathways for some dwarf galaxies.
