文章基本信息

标题：Global survey of star clusters in the Milky Way
其他标题：VI. Age distribution and cluster formation history
本地全文：下载
作者：A. E. Piskunov ; A. Just ; N. V. Kharchenko 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2018
卷号：614
DOI：10.1051/0004-6361/201732337
语种：English
出版社：EDP Sciences
摘要：Context.The all-sky Milky Way Star Clusters (MWSC) survey provides uniform and precise ages, along with other relevant parameters, for a wide variety of clusters in the extended solar neighbourhood.Aims.In this study we aim to construct the cluster age distribution, investigate its spatial variations, and discuss constraints on cluster formation scenarios of the Galactic disk during the last 5 Gyrs.Methods.Due to the spatial extent of the MWSC, we have considered spatial variations of the age distribution along galactocentric radiusRG, and alongZ-axis. For the analysis of the age distribution we used 2242 clusters, which all lie within roughly 2.5 kpc of the Sun. To connect the observed age distribution to the cluster formation history we built an analytical model based on simple assumptions on the cluster initial mass function and on the cluster mass-lifetime relation, fit it to the observations, and determined the parameters of the cluster formation law.Results.Comparison with the literature shows that earlier results strongly underestimated the number of evolved clusters with agest≳ 100 Myr. Recent studies based on all-sky catalogues agree better with our data, but still lack the oldest clusters with agest≳ 1 Gyr. We do not observe a strong variation in the age distribution alongRG, though we find an enhanced fraction of older clusters (t> 1 Gyr) in the inner disk. In contrast, the distribution strongly varies alongZ. The high altitude distribution practically does not contain clusters witht< 1 Gyr. With simple assumptions on the cluster formation history, the cluster initial mass function and the cluster lifetime we can reproduce the observations. The cluster formation rate and the cluster lifetime are strongly degenerate, which does not allow us to disentangle different formation scenarios. In all cases the cluster formation rate is strongly declining with time, and the cluster initial mass function is very shallow at the high mass end.
关键词：Key wordsenGalaxy: evolutionopen clusters and associations: generalGalaxy: stellar contentgalaxies: fundamental parametersgalaxies: photometrygalaxies: star clusters: general