NGC 1399中X射线点源的中红外和X射线光度关联
Mid-Infrared and X-ray luminosity correlations of X-ray point sources in NGC 1399
摘要：
活动星系核（AGN）的红外和X射线光度与L_{IR} ~ L_{X}相关。此外，5.8和3.6 μm波段之间的红外辐射通量比是活动星系核或类活动星系核行为的一个很好的区分特征。另一方面，银河系X射线双星（GXB）在红外波段是欠亮的，L_{IR} L_{X}。由于邻近星系中的超亮X射线源可能是AGN和GXB之间的中间类，因此研究它们的红外特性是否表明它们类似于哪种天体是很有趣的。我们使用斯皮策IRAC图像，以确定明亮的X射线源，在椭圆星系NGC 1399钱德拉探测到中红外对应。我们发现，对于类活动星系核红外辐射通量比的源，其红外光度与X射线的红外光度有很强的相关性，即L_{IR} ~ L_{X}，而对于其他类活动星系核，两者之间没有相关性。有些前者的对象可能是背景活动星系核。如果它们没有受到背景活动星系核的强烈污染，这个结果将红外-X射线光度相关性推广到L_{X} ~ 10^{39}尔格/秒。我们计算了它们的g-z色，发现明亮的X射线源与红外对应物的光学颜色通常是蓝色的。这与典型的X射线源形成对比，没有主要具有红色光学对应物的IR对应物。我们强调需要这些源的红外或光学光谱来区分背景活动星系核和揭示这些系统的不同环境的X射线发射的效果。
英文摘要：
It is known that the IR and X-ray luminosities of Active Galactic Nuclei (AGN) are correlated with L_{IR} ~ L_{X}. Moreover, the IR flux ratio between the 5.8 and 3.6 μm bands is a good distinguishing characteristic of AGN or AGN-like behaviour. On the other hand, Galactic X-ray binaries (GXB) are under-luminous in the IR with L_{IR} << L_{X}. Since Ultra-luminous X-ray sources in nearby galaxies may be an intermediate class between AGN and GXB, it is interesting to study if their IR properties indicate which kind of objects they resemble. We use Spitzer IRAC images to identify mid-IR counterparts of bright X-ray sources, detected by Chandra in the elliptical galaxy NGC 1399. We find that for sources with AGN-like IR flux ratios, the IR luminosity strongly correlates with that in X-rays, L_{IR} ~ L_{X}, while for the others, there is no correlation between the two. Some of the former objects may be background AGN. If they are not strongly contaminated by background AGN, this result extends the IR-X-ray luminosity correlation down to L_{X} ~ 10^{39} ergs/s. We calculate their g-z colours and find that the bright X-ray sources with IR counterparts are typically blue in optical color. This is in contrast to typical X-ray sources, without IR counterparts which have predominantly red optical counterparts. We highlight the need for IR or optical spectra of these sources to distinguish background AGN and unveil the effect of the X-ray emission on the different environments of these systems.
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