Low Ionization Broad Absorption Lines in Quasars

Summary

ABSTRACT

Low-ionization broad absorption line quasars, also known as Mg II BAL QSOs, are intriguing objects that might represent an evolutionary link between the infrared-luminous aftermaths of galaxy-galaxy collisions and the normal, unshrouded quasars thought by some to result from such collisions. This contribution briefly summarizes Mg II BAL QSO phenomenology, sketches the results of a more detailed analysis of Mg II BAL QSO spectra, and estimates the prodigious kinetic energy outputs of these objects. It appears likely that the kinetic luminosities of these quasars exceed 10% of their radiative luminosities.

INTRODUCTION TO MG II BAL QSOS

Broad absorption-line quasars (BAL QSOs), comprising ∼ 10% of all opticallyselected radio-quiet quasars, have puzzled astronomers for over two decades. Broad, blueshifted absorption features in UV resonance lines like CIV, N V, Si IV, and Lyα show that these quasars are ejecting 10⁴ K material at velocities of up to 0.1c. In the spirit of this conference, we could call the BAL QSO phenomenon “Activity-Induced Mass Transfer in Galaxies”.

We still do not understand how these quasars accelerate the absorbing material to such high velocities. Even though BAL outflows could be telling us something important about the innards of active galactic nuclei, BAL QSOs have been somewhat neglected in recent years, partly because we lack a basic understanding of the acceleration mechanism. The field has progressed more by ruling out possible acceleration mechanisms than by identifying schemes that might work. Weymann, Turnshek, and Christiansen (1985) and Begelman, de Kool, and Sikora (1991) provide particularly insightful analyses of the problems involved in accelerating BAL material.