Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo

Gigi Y. C. Leung; Ryan Leaman; Giuseppina Battaglia; Glenn van de Ven; Alyson M. Brooks; Jorge Peñarrubia; Kim A. Venn

doi:10.1093/mnras/staa3107

paper

Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo

arXiv:2104.04273 · doi:10.1093/mnras/staa3107

Abstract

We present multi-tracer dynamical models of the low mass ( $M_{*} \sim 1 0^{7}$ ), isolated dwarf irregular galaxy WLM in order to simultaneously constrain the inner slope of the dark matter (DM) halo density profile ( $γ$ ) and flattening ( $q_{DM}$ ), and the stellar orbital anisotropy ( $β_{z}, β_{r}$ ). 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 $\sim 2$ reduction in the uncertainties on $γ$ . The mass-anisotropy degeneracy is also partially broken, leading to reductions on uncertainty by $\sim 30%$ on $M_{vir}$ (and $\sim 70%$ at the half-light radius) and $\sim 25%$ on anisotropy. Our inferred value of $γ = 0.3 \pm 0.1$ 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 $q_{DM} = 2 \pm 1$ is consistent with $Λ$ CDM simulations of dwarf galaxy halos. While self-interacting DM (SIDM) models with $σ / m_{X} \sim 0.6$ 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 ( $β_{r}$ ) 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.

arXiv commentarxiv version, published in MNRAS. 23 pages, 14 figures

Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo

Abstract

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