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arXiv 0801.2594astro-ph
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单星系系统中X射线双星频率与星团质量函数关系的初步估计

A First Estimate Of The X-Ray Binary Frequency As A Function Of Star Cluster Mass In A Single Galactic System

D. M. Clark, S. S. Eikenberry, B. R. Brandl, J. C. Wilson, J. C. Carson, C. P. Henderson, T. L. Hayward, D. J. Barry, A. F. Ptak, E. J. M. Colbert

摘要:

我们利用相互作用星系NGC 4038/4039中15个红外星团对应的X射线点源,研究了星团总质量与X射线双星数之间的关系。这个显着的人口X射线/IR协会使我们能够执行,第一次,统计研究的X射线点源及其环境。我们定义了一个量η,它与每单位质量的X射线源的分数有关,作为原子团中原子团质量的函数。我们通过拟合光谱演化模型来计算星系团的质量。考虑到这种方法依赖于集群年龄,我们使用四种不同的年龄分布来探索集群年龄对η值的影响,发现它的变化小于四倍。我们找到了η= 1.7 x 10^-8 M_ \sun^- 1且σ_n = 1.2 x 10^-8 M_ \sun^- 1的这些不同分布的η的平均值。通过χ^2检验,我们证明了η可以表现出正的斜率,但它取决于星系团年龄的假设分布。虽然η的估计不确定性是几个因素,但我们相信这是第一次对这个数量进行“数量级”准确性的估计。我们还比较了我们的研究结果,开放和球状星团演化的理论模型,将每个集群的X射线二进制分数。

英文摘要:

We use the previously-identified 15 infrared star-cluster counterparts to X-ray point sources in the interacting galaxies NGC 4038/4039 (the Antennae) to study the relationship between total cluster mass and X-ray binary number. This significant population of X-Ray/IR associations allows us to perform, for the first time, a statistical study of X-ray point sources and their environments. We define a quantity, η, relating the fraction of X-ray sources per unit mass as a function of cluster mass in the Antennae. We compute cluster mass by fitting spectral evolutionary models to K_s luminosity. Considering that this method depends on cluster age, we use four different age distributions to explore the effects of cluster age on the value of ηand find it varies by less than a factor of four. We find a mean value of ηfor these different distributions of η= 1.7 x 10^-8 M_\sun^-1 with σ_η= 1.2 x 10^-8 M_\sun^-1. Performing a χ^2 test, we demonstrate ηcould exhibit a positive slope, but that it depends on the assumed distribution in cluster ages. While the estimated uncertainties in ηare factors of a few, we believe this is the first estimate made of this quantity to ``order of magnitude'' accuracy. We also compare our findings to theoretical models of open and globular cluster evolution, incorporating the X-ray binary fraction per cluster.

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