Keck HIRES Observations of Intrinsic QSO Absorption Systems

Previous abstract Next abstract

Session 42 -- Metallicity in AGN and the Near-AGN Environment
Oral presentation, 8:30am - 12:30pm, June 14, 1995, 9:20am - 6:30pm

[42.09] Keck HIRES Observations of Intrinsic QSO Absorption Systems

Thomas A. Barlow (California Institute of Technology)

Intrinsic QSO absorption systems offer the opportunity to determine elemental abundances in the QSO environment. It is a distinct and complementary method to deriving such abundances using emission lines.

Since absorption line systems can appear at all redshifts, it is necessary to distinguish intrinsic systems from those due to intervening clouds cosmologically distant from the QSO. The typical broad absorption-line (BAL) system is clearly related to the QSO because such wide structures are only observed near the QSO emission-line redshift. Narrower intrinsic systems can appear indistinguishable from those due to intervening galaxies. High resolution, high signal-to-noise spectroscopy available with the Keck telescope and HIRES provide information which can be used to distinguish these systems. Lines which appear unresolved at low resolution can show characteristics at high resolution which are generally associated with conventional BAL systems.

Intrinsic absorption systems may be characterized into three sub-classes: (i) Gas within galaxies in the same cluster as the QSO, (ii) Gas in the outer parts of the QSO host galaxy, and (iii) Gas close to the QSO central engine which has been accelerated. This last type should be the most easily identified. It is most likely to show metallicities similar to the broad emission-line region.

There are several properties which may distinguish the close QSO systems (iii) from intervening absorbers. These systems: (1) tend to be highly ionized, (2) exhibit partial coverage of the background light source, (3) have ``smooth'' profiles, (4) high outflow velocities, (5) can exhibit time variability, and (6) may show increased fractional polarization within the lines.

Keck HIRES data will be presented which demonstrates some of these properties. The feature of partial coverage shall be shown to have a significant effect on the calculation of column densities and estimates of elemental abundances.

8:30a program listing