A Dynamical Fossil in the Ursa Minor Dwarf Spheroidal Galaxy
A Dynamical Fossil in the Ursa Minor Dwarf Spheroidal Galaxy
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DOI：
10.1086/375522
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发表时间：
2003-04
期刊：
影响因子：
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通讯作者：
J. Kleyna;M. Wilkinson;G. Gilmore;N. Evans
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文献类型：
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作者：
J. Kleyna;M. Wilkinson;G. Gilmore;N. Evans
附近的小熊座矮球状体（UMi dSph）是已知最暗物质主导的星系之一，其中心质量与光的比率M/L约为70。有点奇怪的是，它似乎包含了恒星数密度第二个峰值形式的形态亚结构。通常认为，这个子结构必须是瞬态的，因为它不能生存的~12 Gyr年龄的系统，给出的交叉时间所暗示的UMi的8.8 km s-1的内部速度色散。然而，在这封信中，我们提出的证据表明，子结构有一个冷的运动学签名，并认为UMi的笨拙确实可能是一个原始的人工制品。使用数值模拟，我们表明，子结构是不兼容的尖暗物质晕预测的流行的冷暗物质（CDM）的范例，但与一个未绑定的恒星团晃动内的近谐波潜力的核心暗物质晕来回是一致的。因此，CDM似乎不同意在质量最小，最暗物质占主导地位的星系质谱末端的观测。
The nearby Ursa Minor dwarf spheroidal (UMi dSph) is one of the most dark matter-dominated galaxies known, with a central mass-to-light ratio M/L ~ 70. Somewhat anomalously, it appears to contain morphological substructure in the form of a second peak in the stellar number density. It is often argued that this substructure must be transient, because it could not survive for the ~12 Gyr age of the system, given the crossing time implied by UMi's 8.8 km s-1 internal velocity dispersion. In this Letter, however, we present evidence that the substructure has a cold kinematical signature and argue that UMi's clumpiness could indeed be a primordial artefact. Using numerical simulations, we demonstrate that substructure is incompatible with the cusped dark matter halos predicted by the prevailing cold dark matter (CDM) paradigm but is consistent with an unbound stellar cluster sloshing back and forth within the nearly harmonic potential of a cored dark matter halo. Thus, CDM appears to disagree with observation at the least massive, most dark matter-dominated end of the galaxy mass spectrum.