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arXiv 0812.1400astro-ph
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旋涡星系中年轻星团的质量函数

The mass function of young star clusters in spiral galaxies

S. S. Larsen

摘要:

对旋涡星系盘中的初始星团质量函数(ICMF)进行了约束,并与星爆中的老球状星团和年轻星团的数据进行了比较。我们发现,如果ICMF是一个截止质量(Mc)为10^5兆太阳的几倍的谢歇特函数,并且光学可见星系团的破裂主要是由相对缓慢的长期演化决定的,那么观测到的螺旋盘中最亮星系团的年龄和光度就可以重现。对于这里研究的样本中的所有螺旋,直接用谢克特函数拟合组合集群MF,得出Mc =(2.1+/-0.4 x10 ^5 Msun。在集群穷人和集群丰富的螺旋的MF是统计上无法区分的。Mc= 2.1 × 10^5的Msun Schechter函数也适用于大麦云星云中年轻星系团的MF。如果同样的ICMF适用于银河系,一个M>10^5 Msun的束缚星系团大约每1000万年形成一次,而一个M>10^6 Msun的星系团每50 Gyr才形成一次。从Mc=2.1x10^5的Msun Schechter ICMF中得出的模型星系团总体的光度函数(LF)通常与在旋涡星系中观测到的LF一致。因此,得出结论,在当今的螺旋盘ICMF可以模拟为Schechter函数与Mc = 200,000 Msun。然而,在某些星暴星系中存在大量M>10^6 Msun(甚至M>10^7 Msun)的星系团,这使得螺旋星系的Mc值不太可能具有普适性。在高压环境中,例如由复杂的气体运动学和合并中的反馈所产生的环境中,Mc可以转移到比静止圆盘更高的质量。

英文摘要:

The initial cluster mass function (ICMF) in spiral galaxy discs is constrained and compared with data for old globular clusters and young clusters in starbursts. It is found that the observed ages and luminosities of the brightest clusters in spiral discs can be reproduced if the ICMF is a Schechter function with a cut-off mass (Mc) of a few times 10^5 Msun and disruption of optically visible clusters is dominated by relatively slow secular evolution. A direct Schechter function fit to the combined cluster MF for all spirals in the sample studied here yields Mc = (2.1+/-0.4)x10^5 Msun. The MFs in cluster-poor and cluster-rich spirals are statistically indistinguishable. An Mc=2.1x10^5 Msun Schechter function also fits the MF of young clusters in the Large Magellanic Cloud. If the same ICMF applies in the Milky Way, a bound cluster with M>10^5 Msun will form about once every 10 Myr, while an M>10^6 Msun cluster will form only once every 50 Gyr. Luminosity functions (LFs) of model cluster populations drawn from an Mc=2.1x10^5 Msun Schechter ICMF generally agree with LFs observed in spiral galaxies. It is thus concluded that the ICMF in present-day spiral discs can be modelled as a Schechter function with Mc = 200,000 Msun. However, the presence of significant numbers of M>10^6 Msun (and even M>10^7 Msun) clusters in some starburst galaxies makes it unlikely that the Mc value derived for spirals is universal. In high-pressure environments, such as those created by complex gas kinematics and feedback in mergers, Mc can shift to higher masses than in quiescent discs.

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