Constraining the Milky Way halo shape using thin streams
Constraining the Milky Way halo shape using thin streams
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DOI：
10.1093/mnras/stt1744
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发表时间：
2013-08
影响因子：
4.8
通讯作者：
H. Lux;J. Read;G. Lake;K. Johnston
中科院分区：
文献类型：
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作者：
H. Lux;J. Read;G. Lake;K. Johnston
潮汐流是探测银河系势场形状的有力工具。在本文中，我们介绍了一个简单的测试粒子的方法来适应流数据，使用马尔可夫链蒙特卡罗技术边缘化的祖先的轨道和银河系晕形状参数的不确定性。将其应用到模拟数据的薄流在MW晕，我们表明，即使是非常冷的流，流轨道偏移-在我们的简单方法中没有建模-引入系统的偏差恢复的形状参数。对于我们考虑的流，以及我们对潜在参数化的特定选择，这些误差在晕平坦化参数上约为20%。然而，更大的系统误差可能会出现更一般的流和潜力，这样的偏移需要正确建模，以获得一个公正的恢复潜在的。在评估已知的银河系流中哪些是最具约束力的，我们发现NGC 5466和NGC 5是最有希望的候选者。它们形成了一个有趣的对，因为它们的轨道平面都近似垂直于彼此和圆盘，对MW晕的形状给出了最佳的约束。我们表明，虽然目前的数据，他们的潜在参数的约束是穷人-良好的径向速度数据沿着的105流将提供约束qz -扁平垂直于光盘。此外，正如在一个配套文件中所讨论的，NGC 5466可以提供相当强的限制MW晕形状参数，如果初步的证据，从光滑的轨道向其西部边缘偏离得到证实。
Tidal streams are a powerful probe of the Milky Way (MW) potential shape. In this paper, we introduce a simple test particle method to fit stream data, using a Markov Chain Monte Carlo technique to marginalise over uncertainties in the progenitor's orbit and the Milky Way halo shape parameters. Applying it to mock data of thin streams in the MW halo, we show that, even for very cold streams, stream-orbit offsets - not modelled in our simple method - introduce systematic biases in the recovered shape parameters. For the streams that we consider, and our particular choice of potential parameterisation, these errors are of order ~20% on the halo flattening parameters. However, larger systematic errors can arise for more general streams and potentials; such offsets need to be correctly modelled in order to obtain an unbiased recovery of the underlying potential. Assessing which of the known Milky Way streams are most constraining, we find NGC 5466 and Pal 5 are the most promising candidates. These form an interesting pair as their orbital planes are both approximately perpendicular to each other and to the disc, giving optimal constraints on the MW halo shape. We show that - while with current data their constraints on potential parameters are poor - good radial velocity data along the Pal 5 stream will provide constraints on qz - the flattening perpendicular to the disc. Furthermore, as discussed in a companion paper, NGC 5466 can provide rather strong constraints on the MW halo shape parameters, if the tentative evidence for a departure from the smooth orbit towards its western edge is confirmed.