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arXiv 2005.03682astro-ph.GA
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从积分光谱恢复年龄-金属丰度分布:用邻近核星团的MUSE数据验证

Recovering age-metallicity distributions from integrated spectra: validation with MUSE data of a nearby nuclear star cluster

A. Boecker, M. Alfaro-Cuello, N. Neumayer, I. Martín-Navarro, R. Leaman

摘要:

目前的仪器和光谱分析程序现在能够将恒星系统的综合光谱分解成年龄和金属丰度的分布。这些方法的可靠性很少在附近的系统中进行测试,并已分辨出恒星的年龄和金属丰度。在这里,我们得到的年龄金属丰度分布的人马座矮球状星系的核心,从它的综合MUSE光谱。我们发现了一个占主导地位的老(8-14 Gyr),金属贫乏(-1.5 dex)和一个年轻(1 Gyr),金属丰富(+0.25 dex)的组成部分-与同一MUSE数据集中从单个恒星测量的复杂恒星星族一致。有很好的协议之间的(质量加权)平均年龄和金属丰度的解决和综合分析。年龄和金属指数的差异仅为3%。通过共同添加单个恒星来创建M54的综合光谱,我们发现恢复的年龄金属丰度分布对恒星的星等限制或蓝色水平分支恒星的贡献不敏感-即使包括来自WAGGS调查的额外蓝色波长覆盖。然而,我们发现,最亮的恒星可以诱导一个古老的($>8$ Gyr),富含金属(+0.25 dex)的恒星星族的虚假恢复,这是我们对M54化学富集的理解所无法预料的。M54的整体质量光比为M/L $_{\mathrm{V}}=1.46$,在整个视场中的散射为0.22,我们将其归因于年轻的富含金属的成分的随机贡献。这些发现提供了强有力的证据,复杂的恒星星族分布可以可靠地恢复从河外星系的综合光谱。

英文摘要:

Current instruments and spectral analysis programs are now able to decompose the integrated spectrum of a stellar system into distributions of ages and metallicities. The reliability of these methods have rarely been tested on nearby systems with resolved stellar ages and metallicities. Here we derive the age-metallicity distribution of M54, the nucleus of the Sagittarius dwarf spheroidal galaxy, from its integrated MUSE spectrum. We find a dominant old (8-14 Gyr), metal-poor (-1.5 dex) and a young (1 Gyr), metal-rich (+0.25 dex) component - consistent with the complex stellar populations measured from individual stars in the same MUSE data set. There is excellent agreement between the (mass-weighted) average age and metallicity of the resolved and integrated analyses. Differences are only 3% in age and 0.2 dex metallicitiy. By co-adding individual stars to create M54's integrated spectrum, we show that the recovered age-metallicity distribution is insensitive to the magnitude limit of the stars or the contribution of blue horizontal branch stars - even when including additional blue wavelength coverage from the WAGGS survey. However, we find that the brightest stars can induce the spurious recovery of an old ($>8$ Gyr), metal-rich (+0.25 dex) stellar population, which is otherwise not expected from our understanding of chemical enrichment in M54. The overall derived stellar mass-to-light ratio of M54 is M/L$_{\mathrm{V}}=1.46$ with a scatter of 0.22 across the field-of-view, which we attribute to the stochastic contribution of a young, metal-rich component. These findings provide strong evidence that complex stellar population distributions can be reliably recovered from integrated spectra of extragalactic systems.

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