关于SDSS星系高X射线光度的性质
On the nature of high X-ray luminosities in SDSS galaxies
摘要：
巡天观测显示，有一类天体既具有高X射线光度（Lx > 10^42 erg/s），又在光学波段缺乏可辨别的活动星系核（AGN）。如果这些来源是由恒星形成活动单独提供动力，它们将是已知的最极端的X射线光度恒星形成星系。我们研究了驱动X射线光度的机制，通过研究X射线发射的三个中等红移（z ~ 0.1）的这类例子，从SDSS-DR 5和2XMMp-DR 0目录的互相关。这些源的X射线空间和长期变异性诊断表明，它们是紧凑型X射线发射器。这一结果得到了支持的检测快速短期变化的观察来源之一。所有三个来源的X射线光谱都符合简单的吸收幂律模型，因此没有明显的恒星形成迹象。这些结果表明活动星系核活动是X射线辐射的动力来源。但是为什么这些源没有显示出活动星系核的光学特征呢？我们表明，最可能的解释是，光学活动星系核发射线被稀释的恒星形成的签名，从他们的宿主星系。
英文摘要：
Surveys have revealed a class of object displaying both high X-ray luminosities (Lx > 10^42 erg/s), and a lack of a discernible active galactic nucleus (AGN) in the optical band. If these sources are powered by star formation activity alone, they would be the most extreme X-ray luminosity star forming galaxies known. We have investigated the mechanism driving the X-ray luminosities of such galaxies by studying the X-ray emission of three moderate redshift (z ~ 0.1) examples of this class, selected from a cross-correlation of the SDSS-DR5 and 2XMMp-DR0 catalogues. X-ray spatial and long-term variability diagnostics of these sources suggest that they are compact X-ray emitters. This result is supported by the detection of rapid short term variability in an observation of one of the sources. The X-ray spectra of all three sources are best fitted with a simple absorbed power-law model, thus betraying no significant signs of star formation. These results indicate that the X-ray emission is powered by AGN activity. But why do these sources not display optical AGN signatures? We show that the most likely explanation is that the optical AGN emission lines are being diluted by star formation signatures from within their host galaxies.
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