Detalles de publicación
PP 021028
Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo
(1) Max-Planck Institut fur Astronomie, K ̈onigstuhl 17, D-69117 Heidelberg, Germany; (2) Instituto de Astrof ısica de Canarias, Calle Vıa Lactea s/n, E-38205 La Laguna, Tenerife, Spain; (3) Departamento de Astrof ısica, Universidad de La Laguna, E-38200 La Laguna, Tenerife, Spain; (4) Department of Astrophysics, University of Vienna, Turkenschanzstrasse 17, 1180 Vienna, Austria; (5) Department of Physics & Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Rd, Piscataway, NJ 08854, USA; (6) Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ; (7) Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P2, Canada
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.
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.