Quasar Outflows in the 4D Eigenvector 1 Context
  Gas outflows appear to be a phenomenon shared by the vast majority of quasars. Observations indicate that there is wide range in outflow prominence. In this paper we review how the 4D eigenvector 1 scheme helps to organize observed properties and lead to meaningful constraints on the outflow physical and dynamical processes. 
Paola Marziani and Jack W. Sulentic
astro-ph.CO