The most powerful quasar outflows as revealed by the Civ λ1549 resonance line

Abstract

While quasar outflows may be quasi-ubiquitous, there are significant differences on a source-by- source basis. These differences can be organized along the 4D Eigenvector 1 sequence: at least at low z, with only Population A sources radiating at relatively high Eddington ratio and showing prominent high-velocity outflows in Civ λ1549 line profiles. We discuss in this paper VLT-FORS observations of Civ λ1549 emission line profiles for a high-luminosity sample of Hamburg- ESO quasars and how they are affected by outflow motion as a function of quasar luminosity. Our high- luminosity sample has the notable advantage that the rest frame has been accurately determined from previous VLT-ISAAC observations of Hβ in the J, H, and K bands. This makes measures of inter-line velocity shifts accurate and free of systemic biases. As the redshift increases and the luminosity of the brightest quasars increases, powerful, high-velocity outflows become more frequent. We discuss the outflow contextualisation, fol- lowing the 4DE1 formalism, as a tool for understanding the nature of the so-called weak lined quasars (WLQ) discovered in recent years as a new, poorly understood class of quasars. We estimate the kinetic power associ- ated with Civ λ1549 outflows and suggest that the host galaxies in the most luminous sources likely experience significant feedback.

Accepted for publication in Astrophysics and Space Science