WLM的联合气体和恒星动力学模型：一个位于核心长DM晕内的孤立矮星系
Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo
摘要：
我们提出了多示踪动力学模型的低质量（$M_{*} \sim 10^{7}$），孤立的矮不规则星系WLM，以同时限制内斜率的暗物质（DM）晕密度分布（$γ$）和平坦化（$q_\mathrm{DM}$），和恒星轨道各向异性（$β_{z}, β_{r}$）。对于第一次，我们展示了如何共同约束的质量分布HI气体旋转曲线和离散恒星运动学求解金斯方程导致$\sim2$减少$γ$的不确定性的一个因素。质量各向异性简并也被部分打破，导致$\sim 30\%$对$M_\mathrm{vir}$（和$\sim 70\%$在半光半径）和$\sim 25\%$对各向异性的不确定性降低。我们的推断值$γ= 0.3 \pm 0.1$是强大的晕几何形状，并在良好的协议与恒星反馈驱动DM核心创建的预测。推导出的DM晕与$q_\mathrm{DM} = 2 \pm 1$的长轴几何是一致的矮星系晕的$Λ$ CDM模拟。虽然具有$σ/m_{X} \sim 0.6$的自交互DM（SIDM）模型可以重现该核心DM配置文件，但交互事件可能使光环球形化。因此，同时核心和长形DM晕可能是一个挑战SIDM。最后，我们发现WLM（$β_{r}$）中恒星各向异性的径向分布遵循与经典dSphs，Fornax和Sculptor几乎相同的切向各向异性增加的趋势。鉴于WLM的轨道历史，这一结果可能会引起疑问，这种各向异性是否是潮汐剥离的结果，只有一个近心通道，或者如果它是一个功能，而不是在很大程度上自相似的形成和一些矮星系的演化途径。
英文摘要：
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 ($γ$) and flattening ($q_\mathrm{DM}$), 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 $\sim2$ reduction in the uncertainties on $γ$. 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 $γ= 0.3 \pm 0.1$ 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 $q_\mathrm{DM} = 2 \pm 1$ 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.
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