Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity
Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity
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DOI：
10.1111/j.1365-2966.2012.20767.x
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发表时间：
2012-02
影响因子：
4.8
通讯作者：
M. Marks;P. Kroupa;J. Dabringhausen;M. Pawlowski
中科院分区：
文献类型：
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作者：
M. Marks;P. Kroupa;J. Dabringhausen;M. Pawlowski
最近的研究表明，星系团形成后的残余气体排出在低质量恒星质量函数（PDMF）中留下了印记，从而可以估算某些球状星团（GC）的诞生条件，如质量、半径和星星形成效率。为了解释它们的特征（质量、半径、金属丰度、PDMF），它们的恒星初始质量函数（IMF）必须是头重脚轻的。结果表明，金属丰度越低，GC前云核密度越大，顶重越大，需要IMF的参与。推导的趋势与理论预期定性一致。这一结果与对拱星系团、Westerlund 1、R136和NGC 3603中IMF高质量端形状的估计一致，也与超致密矮星系（UCD）的IMF独立约束一致，后者表明GC和UCD可能是沿沿着同一通道形成的，或者UCD是由GC合并形成的.发现了一个基本面，它描述了前GC云核的IMF随密度和金属丰度的变化。关键词：恒星：形成-恒星：质量函数-恒星：早型-恒星：晚型-球状星团：一般
ABSTRACT Residual-gas expulsion after cluster formation has recently been shown to leave animprint in the low-mass present-day stellar mass function (PDMF) which allowedthe estimation of birth conditions of some Galactic globular clusters (GCs) such asmass, radius and star formation efficiency. We show that in order to explain theircharacteristics (masses, radii, metallicity, PDMF) their stellar initial mass function(IMF) must have been top-heavy. It is found that the IMF is required to becomemore top-heavy the lower the cluster metallicity and the larger the pre-GC cloud-core density are. The deduced trends are in qualitative agreement with theoreticalexpectation. The results are consistent with estimates of the shape of the high-massend of the IMF in the Arches cluster, Westerlund 1, R136 and NGC 3603, as wellas with the IMF independently constrained for ultra-compact dwarf galaxies (UCDs).The latter suggests that GCs and UCDs might have formed along the same channel orthat UCDs formed via mergers of GCs. A fundamental plane is found which describesthe variation of the IMF with density and metallicity of the pre-GC cloud-cores. Theimplications for the evolution of galaxies and chemical enrichment over cosmologicaltimes are expected to be major.Keywords: stars: formation – stars: mass-function – stars: early-type – stars: late-type – globular clusters: general