报告题目：The Intriguing Weak Emission-Line Quasars

报 告 人： Prof. Jianfeng Wu，Xiamen Univ.

报告时间：2018-04-26 14:00

报告地点：蒙民伟科技南楼S727

报告摘要：Strong and broad emission lines in the optical/UV band are a hallmark feature of type 1 quasars. However, during the past ~20 years, the Sloan Digital Sky Survey has discovered ~200 type 1 quasars with weak or no broad emission lines, the so-called "Weak Emission-Line Quasars" (WLQs). Although a small population, WLQs may provide a unique perspective to the quasar broad line region and accretion disk structure. We investigated the nature of WLQs via their X-ray properties and found that about half of the WLQs are X-ray weak by a factor of >3; the fraction is much higher than that of typical type 1 quasars (a few percent). The X-ray weak WLQs have very hard X-ray spectra, indicating substantial absorption. On the other hand, the X-ray normal WLQs have soft X-ray spectra, which is consistent with a high Eddington ratio. Based on these results, we proposed a "shielding gas" model to unify the X-ray weak and X-ray normal WLQs via orientation effect. The thick inner accretion disk caused by a high Eddington ratio may serve the role of shielding gas. I will conclude my talk by discussing the cosmological significance and future perspectives of WLQ study.