Red Giant Winds as Emission Line Clouds (Broad or Narrow) in Active Galactic Nuclei

Extract

It is proposed that the clouds thought responsible for the line emission in AGN are not of uniform density but stratified. Such a stratification may be a result either of their self-gravity or of gas dynamics associated with each cloud (e.g. winds). To fix ideas we assume the latter possibility, we examine the consequences and compare with the observations and the phenomenology of emission line clouds.(For the general properties of these clouds see review by Netzer in this volume). Given the successes of the standard model the reader may wonder why is there any need for revisions. The reasons are given in detail elsewhere (see also Scoville and Norman this volume). In brief these are the drag of clouds though the confining medium, the excessive accretion rates implied by the standard model, the response of the line radiation to changes in the continuum, and the lack of a dynamical mechanism for cloud formation. Finally, in the “standard” picture the narrow line clouds are a distinct population with separate dynamics and origin.