早型星系II球状星团的光学/近红外巡天。GC系统的年龄及其与星系形态的关系
An optical/NIR survey of globular clusters in early-type galaxies II. Ages of GC systems and the relation to galaxy morphology
摘要：
内容：利用光学和近红外颜色组合对河外球状星团系统进行的一些光度学研究表明，存在着很大一部分中等年龄（2-8 Gyrs）的球状星团。目的：研究14个E/S 0星系GC系统的年龄分布。研究方法：我们对不同星系中GC系统的（g-z）与（g-K）双色图进行了差分比较，以了解是否存在年龄差异的迹象。我们还用几个简单的恒星星族模型比较了不同的GC系统。结果：椭圆星系GC的平均年龄没有显著差异。另一方面，S 0星系显示出年轻GC的证据。令人惊讶的是，这似乎是由更贫金属的集群驱动的。NGC 4365中GC的年龄分布似乎与其他大椭圆星系（如NGC 4486、NGC 4649）相似。帕多瓦SSPs最近发布的等时线为老年人（14陀螺仪）显示较少的偏移相对于测光比以前公布的模型。结论：我们认为E型星系大部分GC的形成时间比S 0型星系短，形成时间也比S 0型星系早。后一种星系类型似乎有更长的GC形成/聚集期。
英文摘要：
Context: Some photometric studies of extragalactic globular cluster (GC) systems using the optical and near-infrared colour combination have suggested the presence of a large fraction of intermediate-age (2-8 Gyrs) GCs. Aims: We investigate the age distributions of GC systems in 14 E/S0 galaxies. Methods: We carry out a differential comparison of the (g-z) vs. (g-K) two-colour diagrams for GC systems in the different galaxies in order to see whether there are indications of age differences. We also compare the different GC systems with a few simple stellar population models. Results: No significant difference is detected in the mean ages of GCs among elliptical galaxies. S0 galaxies on the other hand, show evidence for younger GCs. Surprisingly, this appears to be driven by the more metal-poor clusters. The age distribution of GCs in NGC4365 seems to be similar to that of other large ellipticals (e.g. NGC4486, NGC4649). Padova SSPs with recently released isochrones for old ages (14 Gyrs) show less of an offset with respect to the photometry than previously published models. Conclusions: We suggest that E type galaxies assembled most of their GCs in a shorter and earlier period than S0 type galaxies. The latter galaxy type, seems to have a more extended period of GC formation/assembly.
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