Ursa Major: A Missing Low-Mass CDM Halo?
Ursa Major: A Missing Low-Mass CDM Halo?
复制标题
大熊座：失踪的低质量 CDM 光环？
DOI：
10.1086/491654
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
G. Gilmore
中科院分区：
文献类型：
--
作者：
J. Kleyna;M. Wilkinson;N. Evans;G. Gilmore
最近发现的大熊座矮球状（dSph）候选星系的亮度比之前已知的最暗的dSph、And IX、天龙座和小熊座低约5-8倍。在这封信中，我们提出了七个颜色星等选择大熊座候选星的速度测量。根据金属丰度和速度，其中两颗是明显的非成员，其余五颗恒星的系统日心速度为= -52.45 ± 4.27 km s-1，中心视线速度色散为9.3 km s-1，95%的置信度为9.5 km s-1。假设UMa处于动力学平衡，它显然是暗物质主导的，不可能是一个像球状星团那样的纯粹恒星系统。它有一个推断的中央质光比的M/L ~ 500 M反射/L，并根据我们对其他dSphs的研究，可能拥有一个更大的总质光比。乌玛星系的低光度出乎意料的巨大--事实上，乌玛星系似乎是迄今为止发现的最暗物质主导的星系。UMa中存在如此多的暗物质立即表明它可能是冷暗物质（CDM）范式预测的失踪的低质量星系群的成员。由于dSph质量和光度之间的弱相关性，我们的银河系完全有可能围绕着一群暗矮星。
The recently discovered Ursa Major dwarf spheroidal (dSph) galaxy candidate is about 5-8 times less luminous than the faintest previously known dSphs, And IX, Draco, and Ursa Minor. In this Letter, we present velocity measurements of seven color-magnitude-selected Ursa Major candidate stars. Two of them are apparent nonmembers based on metallicity and velocity, and the remaining five stars yield a systemic heliocentric velocity of = -52.45 ± 4.27 km s-1 and a central line-of-sight velocity dispersion of ⟨v2⟩1/2 = 9.3 km s-1, with 95% confidence that ⟨v2⟩1/2 > 6.5 km s-1. Assuming that UMa is in dynamical equilibrium, it is clearly dark matter-dominated and cannot be a purely stellar system like a globular cluster. It has an inferred central mass-to-light ratio of M/L ~ 500 M☉/L☉ and, based on our studies of other dSphs, may possess a much larger total mass-to-light ratio. UMa is unexpectedly massive for its low luminosity—indeed, UMa appears to be the most dark matter-dominated galaxy yet discovered. The presence of so much dark matter in UMa immediately suggests that it may be a member of the missing population of low-mass galaxies predicted by the cold dark matter (CDM) paradigm. Given the weak correlation between dSph mass and luminosity, it is entirely likely that a population of dark dwarfs surrounds our Galaxy.