Implications of infalling Fe II - emitting clouds in active galactic nuclei: anisotropic properties

TL;DR

This paper explores how infalling Fe II-emitting clouds in quasars influence observed spectral features, linking their properties to the Eddington ratio and explaining longstanding emission line mysteries.

Contribution

It demonstrates that infalling, shielded Fe II-emitting clouds with high column densities can account for spectral observations and their correlation with the Eddington ratio.

Findings

Fe II emission originates from infalling, shielded clouds.

The force multiplier in Fe II gas is approximately 10^3 - 10^4.

Infall occurs in clouds with large column densities, explaining spectral correlations.

Abstract

We investigate consequences of the discovery that Fe II emission in quasars, one of the spectroscopic signatures of "Eigenvector 1", may originate in infalling clouds. Eigenvector 1 correlates with the Eddington ratio L/L_Edd so that Fe II/Hbeta increases as L/L_Edd increases. We show that the "force multiplier", the ratio of gas opacity to electron scattering opacity, is ~ 10^3 - 10^4 in Fe II-emitting gas. Such gas would be accelerated away from the central object if the radiation force is able to act on the entire cloud. As had previously been deduced, infall requires that the clouds have large column densities so that a substantial amount of shielded gas is present. The critical column density required for infall to occur depends on L/L_Edd, establishing a link between Eigenvector 1 and the Fe II/Hbeta ratio. We see predominantly the shielded face of the infalling clouds rather than the symmetric distribution of emitters that has been assumed. The Fe II spectrum emitted by the shielded face is in good agreement with observations thus solving several long-standing mysteries in quasar emission lines.