Globular clusters in the outer halo of M 31
Globular clusters in the outer halo of M 31
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DOI：
10.1051/0004-6361/201834748
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发表时间：
2019-01
影响因子：
6.5
通讯作者：
Song-Yun Wang;Jun Ma;Jifeng Liu
中科院分区：
文献类型：
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作者：
Song-Yun Wang;Jun Ma;Jifeng Liu
本文对m31外晕中的53个球状星团（GCs）进行了光度测量，包括GALEX远紫外（FUV）和近紫外（NUV）， SDSS ugriz， 15个BATC中波段滤光片和2个mass jhk波段。通过将多色光度法与恒星群合成模型进行比较，我们确定了这些gc的金属丰度、年龄和质量，旨在探索m31的合并/吸积历史。我们没有发现金属丰度和质量随消投影半径变化的明显趋势。小于~ 8gyr的光晕GCs大多位于去投影半径约100kpc处，但这可能是由于选择效应。我们还发现光晕gc的金属丰度与其空间相关的亚结构一致，这进一步证明了它们之间的物理联系。m31中的盘状和晕状gc均表现出双峰型的光度分布。然而，我们应该强调的是，有更多微弱的晕状GCs是在盘中看不到的。光晕gc的双峰光度函数可能反映了其原始宿主的不同起源或演化环境。m31晕状gc包括一个中间金属丰度基团（- 1.5 < [Fe/H] < - 0.4）和一个金属贫金属基团（[Fe/H] < - 1.5），而盘状gc则有一个富金属基团。m31和银河系（MW）的光晕GCs有相当大的差异。m31的光环GCs总数大约是MW的3倍，然而m31的光环GCs大约是MW的6倍。与m31的光环gc相比，MW的光环gc大多是金属贫乏的。大量的光环gc和高金属丰度成分都表明m31有活跃的合并历史。
In this paper, we present photometry of 53 globular clusters (GCs) in the M 31 outer halo, including the GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV), SDSS ugriz, 15 intermediate-band filters of BATC, and 2MASS JHKs bands. By comparing the multicolour photometry with stellar population synthesis models, we determine the metallicities, ages, and masses for these GCs, aiming to probe the merging/accretion history of M 31. We find no clear trend of metallicity and mass with the de-projected radius. The halo GCs younger than ∼8 Gyr are mostly located at the de-projected radii around 100 kpc, but this may be due to a selection effect. We also find that the halo GCs have consistent metallicities with their spatially associated substructures, which provides further evidence of the physical association between them. Both the disc and halo GCs in M 31 show a bimodal luminosity distribution. However, we should emphasise that there are more faint halo GCs which are not seen in the disc. The bimodal luminosity function of the halo GCs may reflect a different origin or evolution environment in their original hosts. The M 31 halo GCs include one intermediate metallicity group (−1.5 < [Fe/H] < −0.4) and one metal-poor group ([Fe/H] < −1.5), while the disc GCs have one metal-rich group more. There are considerable differences between the halo GCs in M 31 and the Milky Way (MW). The total number of GCs in M 31 is approximately three times greater than in the MW, however M 31 has about six times more halo GCs than the MW. Compared to the halo GCs of M 31, those of the MW are mostly metal-poor. Both the numerous halo GCs and the higher-metallicity component are suggestive of an active merger history of M 31.