UCD的本质：来自扩展样本和同质数据库的内部动力学
The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database
摘要：
利用FLAMES/Giraffe在VLT上获得了天炉座星系团中23个超致密矮星系（UCD）的高分辨光谱，这些星系的M_V为-10.4>-13.5等（10^6<M/M_*<10^8）。这是迄今为止组装的UCD内部动态的最大同质数据集。我们推导出动态M/L比为15 UCD覆盖HST成像。在M_V-sigma平面上，M_V<-12等的UCD与外推的明亮椭圆星系的Faber-Jackson关系一致，而较暗的UCD则更接近外推的球状星团（GC）关系。在给定的金属丰度下，天炉座UCD的M/L比室女座UCD平均低30-40%，这表明天炉座和室女座UCD之间的年龄或暗物质含量可能存在差异。对于我们的穹窿UCD样本，我们发现M/L比与质量之间没有显着相关性。我们将我们的数据与10^4<M/M_*<10^8的致密恒星系统的M/L比测量结果相结合，并将所有M/L估计值标准化为太阳金属丰度。我们发现UCD（M > 2* 10^6M_*）的M/L比是GC（M < 2* 10^6M_*）的两倍。我们发现，恒星星族模型往往低估的动态M/L比的UCD和高估的GC。考虑到恒星球状体的标度关系，UCD沿“基本流形”排列良好，构成了星系序列的小尺度端。当r_e >~ 7 pc时，UCD的排列特别清楚，这对应于超过哈勃时间的动力学弛豫时间。相比之下，GC表现出更广泛的散射，并且似乎没有沿着歧管对齐。我们认为UCD是最小的动力学非弛豫恒星系统，M > 2* 10^6M *，7<r_e<100 pc.未来的研究应旨在解释升高的M/L比的UCDs和环境依赖性，其属性。
英文摘要：
We have obtained high-resolution spectra of 23 ultra-compact dwarf galaxies (UCDs) in the Fornax cluster with -10.4>M_V>-13.5 mag (10^6<M/M_*<10^8), using FLAMES/Giraffe at the VLT. This is the largest homogeneous data set of UCD internal dynamics assembled to date. We derive dynamical M/L ratios for 15 UCDs covered by HST imaging. In the M_V-sigma plane, UCDs with M_V<-12 mag are consistent with the extrapolated Faber-Jackson relation for luminous ellipticals, while fainter UCDs are closer to the extrapolated globular cluster (GC) relation. At a given metallicity, Fornax UCDs have on average 30-40% lower M/L ratios than Virgo UCDs, suggesting possible differences in age or dark matter content between Fornax and Virgo UCDs. For our sample of Fornax UCDs we find no significant correlation between M/L ratio and mass. We combine our data with available M/L ratio measurements of compact stellar systems with 10^4<M/M_*<10^8, and normalise all M/L estimates to solar metallicity. We find that UCDs (M > 2*10^6 M_*) have M/L ratios twice as large as GCs (M < 2*10^6 M_*). We show that stellar population models tend to under-predict dynamical M/L ratios of UCDs and over-predict those of GCs. Considering the scaling relations of stellar spheroids, UCDs align well along the 'Fundamental Manifold', constituting the small-scale end of the galaxy sequence. The alignment for UCDs is especially clear for r_e >~ 7 pc, which corresponds to dynamical relaxation times that exceed a Hubble time. In contrast, GCs exhibit a broader scatter and do not appear to align along the manifold. We argue that UCDs are the smallest dynamically un-relaxed stellar systems, with M > 2*10^6 M_* and 7<r_e<100 pc. Future studies should aim at explaining the elevated M/L ratios of UCDs and the environmental dependence of their properties.
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