The diversity of quasars unified by accretion and orientation

摘要

类星体是由物质向星系中心的超大质量黑洞上的吸积来提供动力的。在这篇论文中，Yue Shen和Luis Ho试图解决一个长期未决的问题: 类星体所表现出的显著波谱多样性的物理基础。基于来自很大一组均一的类星体的数据，本文作者证明，所观测到的类星体性质之差异可归于两个基本参数: 向中心黑洞上的吸积速度（以"Eddington ratio"形式来测定，由光度除以黑洞质量获得）和接近黑洞绕轨运行的气体云的一种盘状分布的取向。%Quasars are rapidly accreting supermassive black holes at the centres of massive galaxies. They display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions of the regions close to the central engine. These properties, however, are not random, but form well-defined trends. The dominant trend is known as 'Eigenvector 1', in which many properties correlate with the strength of optical iron and [O_Ⅲ] emission. The main physical driver of Eigenvector 1 has long been suspected to be the quasar luminosity normalized by the mass of the hole (the 'Eddington ratio'), which is an important parameter of the black hole accretion process. But a definitive proof has been missing. Here we report an analysis of archival data that reveals that the Eddington ratio indeed drives Eigenvector 1. We also find that orientation plays a significant role in determining the observed kinematics of the gas in the broad-line region, implying a flattened, disk-like geometry for the fast-moving clouds close to the black hole. Our results show that most of the diversity of quasar phenomenology can be unified using two simple quantities: Eddington ratio and orientation.