Dynamical mass estimates for two luminous star clusters in galactic merger remnants
Dynamical mass estimates for two luminous star clusters in galactic merger remnants
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星系合并遗迹中两个发光星团的动态质量估计
DOI：
10.1051/0004-6361:20054177
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发表时间：
2005
影响因子：
6.5
通讯作者：
M. Zoccali
中科院分区：
文献类型：
--
作者：
N. Bastian;N. Bastian;R. Saglia;P. Goudfrooij;M. Kissler;C. Maraston;F. Schweizer;M. Zoccali
我们给出了用安装在ESO甚大望远镜上的UVES光谱仪获得的银河系合并残余物中两个极大质量星团的高色散光谱。其中一个星团W30位于老合并残余区NGC7252附近，其速度弥散系数和有效半径分别为27.5×10-5pc和9.3×pm1.7×pc，距离S-1和Rm=9.3pm1.7×pc。另一个星系团G114位于~3Gyr老合并残余物NGC-1316中，更为致密，距离S-1星团的速度弥散为$R_(？)=4.08\pm0.55$pc，速度弥散为$\sigma=42.1\pm2.8$10公里。这些测量允许估计两个团簇的维里质量，得到${\cal{M}_{\rm dyn}(W30)=1.59(\pm0.26)\x 10^7~{\cal{M}}_{\odot}$和${\cal{M}_{\rm dyn}(G114)=1.64(\pm0.13)\x 10^7~{\cal{M}}_{\odot}$。这两个星系团都非常大，比银河系中最大的球状星团重三倍以上。对于这两个星系团，我们测量了光质量比，当与适当年龄的简单恒星群(SSP)模型相比时，符合Kroupa类型的恒星质量函数。使用文献中的测量结果，我们发现SSP模型(具有潜在的Kroupa或Salpeter类型的恒星质量函数)与星系团的光质量比的匹配程度与年龄有很强的相关性。基于这一结果，我们认为最年轻的星系团的光质量比的大散射不是由于潜在恒星质量函数的变化，而是因为年轻星系团的内部动力学迅速变化。基于抽样统计，我们认为，虽然W30和G114质量非常大，但它们是在连续的幂函数星团质量分布中形成的最大质量的星系团。最后，基于旧球状星团、年轻质量星团(YMC)、超致密矮星系(UCD)和矮球过渡天体(DGTO)在κ空间中的位置，我们得出结论：(1)UCDS和DGTO与星团的高端质量端一致；(2)YMC占据的参数空间比旧球状星团大得多，这与星团优先分裂的观点一致。
We present high-dispersion spectra of two extremely massive star clusters in galactic merger remnants, obtained using the UVES spectrograph mounted on the ESO Very Large Telescope. One cluster, W30, is located in the ~500 Myr old merger remnant NGC 7252 and has a velocity dispersion and effective radius of $\sigma=27.5\pm2.5$ km s -1 and $R_{\rm eff}=9.3\pm1.7$ pc, respectively. The other cluster, G114, located in the ~3 Gyr old merger remnant NGC 1316, is much more compact, $R_{\rm eff}=4.08\pm0.55$ pc, and has a velocity dispersion of $\sigma=42.1\pm2.8$ km s -1 . These measurements allow an estimate of the virial mass of the two clusters, yielding ${\cal{M}}_{\rm dyn}(W30)=1.59(\pm0.26)\times 10^7~{\cal{M}}_{\odot}$ and ${\cal{M}}_{\rm dyn}(G114)=1.64(\pm0.13)\times 10^7~{\cal{M}}_{\odot}$. Both clusters are extremely massive, being more than three times heavier than the most massive globular clusters in the Galaxy. For both clusters we measure light-to-mass ratios, which when compared to simple stellar population (SSP) models of the appropriate age, are consistent with a Kroupa-type stellar mass function. Using measurements from the literature we find a strong age dependence on how well SSP models (with underlying Kroupa or Salpeter-type stellar mass functions) fit the light-to-mass ratio of clusters. Based on this result we suggest that the large scatter in the light-to-mass ratio of the youngest clusters is not due to variations in the underlying stellar mass function, but instead to the rapidly changing internal dynamics of young clusters. Based on sampling statistics we argue that while W30 and G114 are extremely massive, they are consistent with being the most massive clusters formed in a continuous power-law cluster mass distribution. Finally, based on the positions of old globular clusters, young massive clusters (YMCs), ultra-compact dwarf galaxies (UCDs) and dwarf-globular transition objects (DGTOs) in κ -space we conclude that 1) UCDs and DGTOs are consistent with the high mass end of star clusters and 2) YMCs occupy a much larger parameter space than old globular clusters, consistent with the idea of preferential disruption of star clusters.