标题： 河外球状星团在近红外中的研究 I：M87 与 NGC 4478 的比较 显示英文标题

标题： Extragalactic Globular Clusters in the Near Infrared I: A comparison between M87 and NGC 4478

摘要： 我们比较了室女座中M87（中心巨椭圆星系）和NGC 4478（室女座中亮度中等的星系，投影上靠近M87）球状星团的光学和近红外颜色。结合使用哈勃空间望远镜上的WFPC2获得的V和I测光数据以及使用凯克望远镜上的NIRC获得的Ks测光数据1，我们发现M87的颜色范围很广，并且之前检测到的双峰性。我们确认NGC 4478仅拥有一个蓝色子种群的球状星团，并且现在表明这些星团的V-I和V-K颜色与银河系和M31晕中的球状星团非常相似。很可能，金属丰富子种群从未在这个星系周围形成（而不是后来形成又被摧毁），可能是因为其金属丰富的气体在其穿过室女座星系团中心时被剥离了。V-I和V-K颜色接近旧种群的SSP模型预测颜色。然而，M87拥有一些红色星团，这些星团最合理的解释是中间年龄（几十亿年）。总体而言，有证据表明红色金属丰富子种群具有复杂的颜色结构，并且本身由跨越大金属丰度和可能年龄范围的星团组成。这与目前观测到的所有星系中看起来非常均质的蓝色贫金属种群形成对比。 显示英文摘要

摘要： We compare optical and near infrared colours of globular clusters in M87, the central giant elliptical in Virgo, and NGC 4478, an intermediate luminosity galaxy in Virgo, close in projection to M87. Combining V and I photometry obtained with the WFPC2 on HST and Ks photometry obtained with the NIRC on Keck 1, we find the broad range in colour and previously detected bi-modality in M87. We confirm that NGC 4478 only hosts a blue sub-population of globular clusters and now show that these clusters' V-I and V-K colours are very similar to those of the halo globular clusters in Milky Way and M31. Most likely, a metal-rich sub-population never formed around this galaxy (rather than having formed and been destroyed later), probably because its metal-rich gas was stripped during its passage through the centre of the Virgo cluster. The V-I, V-K colours are close to the predicted colours from SSP models for old populations. However, M87 hosts a few red clusters that are best explained by intermediate ages (a few Gyr). Generally, there is evidence that the red, metal-rich sub-population has a complex colour structure and is itself composed of clusters spanning a large metallicity and, potentially, age range. This contrasts with the blue, metal-poor population which appears very homogeneous in all galaxies observed so far.