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arXiv · 1801.07373

What to expect from dynamical modelling of galactic haloes II: the spherical Jeans equation

Wenting Wang·Jiaxin Han·Shaun Cole·Surhud More·Carlos Frenk·Matthieu Schaller
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Abstract

The spherical Jeans equation (SJE) is widely used in dynamical modelling of the Milky Way (MW) halo potential. We use haloes and galaxies from the cosmological Millennium-II simulation and hydrodynamical APOSTLE simulations to investigate the performance of the SJE in recovering the underlying mass profiles of MW mass haloes. The best-fitting halo mass and concentration parameters scatter by 25% and 40% around their input values, respectively, when dark matter particles are used as tracers. This scatter becomes as large as a factor of 3 when using star particles instead. This is significantly larger than the estimated statistical uncertainty associated with the use of the SJE. The existence of correlated phase-space structures that violate the steady state assumption of the SJE as well as non-spherical geometries are the principal sources of the scatter. Binary haloes show larger scatter because they are more aspherical in shape and have a more perturbed dynamical state. Our results confirm the previous study of Wang et al. (2017) that the number of independent phase-space structures sets an intrinsic limiting precision on dynamical inferences based on the steady state assumption. Modelling with a radius-independent velocity anisotropy, or using tracers within a limited outer radius, result in significantly larger scatter, but the ensemble-averaged measurement over the whole halo sample is approximately unbiased.

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Wenting Wang, Jiaxin Han, Shaun Cole, Surhud More, Carlos Frenk, Matthieu Schaller. 2018-03-13. What to expect from dynamical modelling of galactic haloes II: the spherical Jeans equation. https://doi.org/10.1093/mnras%2Fsty706

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