超亮X射线源和大质量贫金属恒星的遗迹
Ultra-luminous X-ray sources and remnants of massive metal-poor stars
摘要：
大质量贫金属恒星可能会通过直接坍缩形成质量为25<=mBH/Msun<=80的大质量恒星黑洞（BH）。我们推导出通过这种机制预计每个星系形成的大质量黑洞（NBH）的数量。这种大质量的黑洞可能为大多数观测到的超亮X射线源（ULX）提供动力。我们选择了一个样本的64个星系的X射线覆盖，恒星形成率（SFR）和金属丰度的测量。我们发现NBH与该样本中每个星系观察到的ULX（NULX）数量相关。我们讨论了我们的模型对SFR和金属丰度的依赖性。SFR被认为是至关重要的，与以前的研究一致。在我们的模型中，金属丰度起着一定的作用，因为较低的金属丰度增强了大规模BH的形成。与我们的模型相一致，数据表明，NULX，归一化到SFR，和金属丰度之间可能有一个很好的关系。为了证实我们的结果，需要更大和更均匀的金属丰度测量样品。
英文摘要：
Massive metal-poor stars might form massive stellar black holes (BHs), with mass 25<=mBH/Msun<=80, via direct collapse. We derive the number of massive BHs (NBH) that are expected to form per galaxy through this mechanism. Such massive BHs might power most of the observed ultra-luminous X-ray sources (ULXs). We select a sample of 64 galaxies with X-ray coverage, measurements of the star formation rate (SFR) and of the metallicity. We find that NBH correlates with the number of observed ULXs per galaxy (NULX) in this sample. We discuss the dependence of our model on the SFR and on the metallicity. The SFR is found to be crucial, consistently with previous studies. The metallicity plays a role in our model, since a lower metallicity enhances the formation of massive BHs. Consistently with our model, the data indicate that there might be an anticorrelation between NULX, normalized to the SFR, and the metallicity. A larger and more homogeneous sample of metallicity measurements is required, in order to confirm our results.
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