2 M31外晕球状星团的质量测光和年龄估算
2MASS photometry and age estimate of globular clusters in the outer halo of M31
摘要：
本文首次给出了M31远外区10个经典球状星团的2 MASS成像的J、H和K_s测光结果。结合以往文献中的V和I光度数据，我们构建了J-K_s和V-I之间的颜色-颜色图。通过比较综合光度测量与演化模型，我们估计这些集群的年龄。结果表明，所有年龄组均大于$3\times 10^9$岁，其中4例大于10岁，其余6例介于3-8岁之间。这些外晕GC的质量从$7.0\times 10^4 M_sun$到$1.02\times 10^6 M_sun$。我们认为，年龄、金属丰度和距离模量相近的GC 2和GC 3，如果不是在原地形成{ \it}，则是从同一个卫星星系吸积而来的。统计结果表明，这10个M31外晕GC的年龄和金属丰度不随投影径向位置的变化而变化，不存在年龄与金属丰度的关系。
英文摘要：
We present the first photometric results in J, H, and K_s from 2MASS imaging of 10 classical globular clusters in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed the color-color diagram between J-K_s and V-I. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that, all of these clusters are older than $3\times 10^9$ yrs, of which 4 are older than 10 Gyrs and the other 6 are in intermediate ages between 3-8 Gyrs. The masses for these outer halo GCs are from $7.0\times 10^4 M_sun$ to $1.02\times 10^6 M_sun$. We argued that, GC2 and GC3, the ages, metallicities and the distance moduli of which are nearly the same, were accreted from the same satellite galaxy, if they did not form {\it in situ}. The statistical results show that, ages and metallicities for these 10 M31 outer halo GCs do not vary with projected radial position, and the relationship between age and metallicity doest not exit.
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