Intrinsic AGN Absorption Lines

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. Intrinsic absorption lines are thus valuable probes of the kinematics, physical conditions and elemental abundances in the gas near AGNs. Studies of intrinsic absorbers have historically emphasized the broad absorption lines (BALs) in quasars. Today we recognize a wider variety of intrinsic lines in a wider range of objects. For example, we now know that Seyfert 1 galaxies (the less luminous cousins of quasars) have intrinsic absorption. We also realize that intrinsic lines can form in a range of AGN environments — from the dynamic inner regions like the BALs, to the more quiescent outer host galaxies >10 kpc away. This article provides a brief introduction to current observational and theoretical work on intrinsic AGN absorbers.