THE BROAD-LINE REGION OF ACTIVE GALACTIC NUCLEI REVISITED

Broad emission lines which are the most characteristic features of Active Galactic Nuclei and quasars can be separated into two distinct systems: the "high-ionization lines" (HIL) and "low-ionization lines" (LIL). HILs are emitted by low-pressure optically-thin "clouds" illuminated by a rather soft continuum radiation; LILs are produced by a high-pressure optically-thick medium, illuminated mainly by hard X-rays, possibly the outer region of an accretion disk. This recent version of the photoionization model of the broad-line region is still unable to provide a consistent explanation of the unusual intensities of the iron Fe II lines in strong optical Fe II emitters.

宽发射线是活动星系核和类星体最具特征的表现，可分为两个不同的系统：“高电离线”（HIL）和“低电离线”（LIL）。高电离线是由低压、光学薄的“云”发射出来的，这些“云”受到相当软的连续辐射的照射；低电离线是由高压、光学厚的介质产生的，主要受到硬X射线的照射，可能是吸积盘的外部区域。这个宽线区光致电离模型的最新版本仍然无法对强光学铁II发射体中铁Fe II线的异常强度提供一致的解释。