标题： 2XMM 高光度X射线源候选体在邻近星系中 显示英文标题

标题： 2XMM Ultraluminous X-Ray Source Candidates in Nearby Galaxies

摘要： 超亮X射线源（ULXs）是目前已知最神秘的X射线明亮天体之一。普遍认为它们不能包含像活动星系中那样的大质量黑洞，但它们似乎比我们更了解的银河系X射线双星（XRB）伙伴要显著明亮，同时与它们呈现出有趣的差异和相似性的组合。通过研究这些源的大规模代表性样本，我们希望能够增强对它们的理解。为此，我们通过将2XMM意外调查与第三版明亮星系参考目录进行交叉相关，得出了一个包含470个ULX候选者的650个X射线检测目录，这些ULX位于238个近邻星系中。所提出的专门目录在数量和背景污染贡献方面都显著优于以前发表的目录，例如，远处类星体的贡献估计最多为24%，但更可能是约17%。为了进行种群研究，我们定义了一个“完整”的子样本，该样本由灵敏度限制低于10^39 erg/s的星系观测组成。该样本的光度函数与简单的幂律一致。尽管我们没有发现之前报告过的高亮度截断的统计需求，但我们无法排除其存在。此外，我们发现对于与螺旋星系相关的ULX，单位星系质量的ULX数量随着星系质量的增加而减少，这与以前的结果大致一致，但对于与椭圆星系相关的源，它与星系质量无关而保持恒定。 显示英文摘要

摘要： Ultraluminous X-ray sources (ULXs) are some of the most enigmatic X-ray bright sources known to date. It is generally accepted that they cannot host black holes as large as those associated with active galaxies, but they appear to be significantly more luminous than their better understood Galactic X-ray binary (XRB) cousins, while displaying an intriguing combination of differences and similarities with them. Through studying large, representative samples of these sources we may hope to enhance our understanding of them. To this end, we derive a large catalogue of 650 X-ray detections of 470 ULX candidates, located in 238 nearby galaxies, by cross correlating the 2XMM Serendipitous Survey with the Third Reference Catalogue of Bright Galaxies. The presented dedicated catalogue offers a significant improvement over those previously published both in terms of number and the contribution of background contaminants, e.g. distant quasars, which we estimate to be at most 24 per cent, but more likely ~17 per cent. To undertake population studies, we define a `complete' sub-sample of sources compiled from observations of galaxies with sensitivity limits below 10^39 erg/s. The luminosity function of this sample is consistent with a simple power-law. Although we do not find any statistical requirement for a high luminosity cut-off, as has been reported previously, we are not able to rule out its presence. Also, we find that the number of ULXs per unit galaxy mass decreases with increasing galaxy mass for ULXs associated with spiral galaxies, in broad agreement with previous results, but is consistent with being constant with galaxy mass for sources associated with elliptical galaxies.