Department of Astronomy: Quasars and Active Galaxies

Quasars & Active Galaxies

Quasar Absorption Line Systems

Gaseous material along our sight lines to distant quasars or, more generally, active galactic nuclei (AGNs) will absorb light according to the amounts and range of ions present. Strong absorption lines are common in rest-frame UV spectra of AGNs due to a variety of resonant transitions, for example the HI Lyman series lines (most notably Ly-alpha 1216) and high-ionization doublets like CIV 1549,1551. The lines are called intrinsic if the absorbing gas is physically related to the AGN, e.g. if the absorber resides broadly within the radius of the AGN's surrounding "host" galaxy. A recent review by Fred Hamann (astro-ph/9911505) summarizes the current status of this field.

The figures on this page show examples of the different classes of intrinsic AGN absorption lines. The broad absorption lines (BALs) clearly identify high velocity outflows from quasar engines, while the narrow absorption lines (NALs) can form potentially in a variety of locations. We are involved in studies to identify intrinsic absorption lines, and use them to understand the physical conditions, outflow dynamics and elemental abundances in AGN environments.

Detached BALs in the quasar PG 1254+047 (Hamann 1998). The BALs are labeled just above the spectrum. The wavelengths of prominent broad emission lines are marked across the top. The Flux has units 10^-15 ergs s^-1 cm^-2 Å^-1.

Intrinsic absorption in the quasar PG 0935+417 (Hamann et al 1997). A system of associated NALs is labeled above the spectrum, with open brackets showing the doublet separations. A mini-BAL due to CIV blueshifted by ~51,000 km/s is labeled below. The Flux has units 10^-15 ergs s^-1 cm^-2 Å^-1.

This page created by Matthias Dietrich and Craig Warner
Questions or comments should be sent to: Matthias Dietrich

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