2001ApJ...550..142H

Associated absorption lines (AALs) are valuable probes of the gaseous environments near quasars. Here we discuss high-resolution (6.7 km.s^–1) spectra of the AALs in the radio-loud quasar 3C 191 (redshift z=1.956). The measured AALs have ionizations ranging from Mg I to N V and multicomponent profiles that are blueshifted by ∼400 to ∼1400 km.s^–1 relative to the quasar's broad emission lines. These data yield the following new results: (1) The strengths of excited-state Si II^* AALs indicate a density of ∼300 cm^–3 in the Si⁺ gas. (2) If the gas is photoionized, this density implies a distance of ∼28 kpc from the quasar. Several arguments suggest that all of the lines form at approximately this distance. (3) The characteristic flow time from the quasar is thus ∼3x10⁷ yr. (4) Strong Mg I AALs identify neutral gas with very low ionization parameter and high density. We estimate n_H≳5x10⁴ cm^–3 in this region, compared to ∼15 cm^–3 where the N V lines form. (5) The total column density is N_H≲4x10¹⁸ cm^–2 in the neutral gas and N_H∼2x10²⁰ cm^–2 in the moderately ionized regions. These column densities are consistent with 3C 191's strong soft X-ray flux and the implied absence of soft X-ray absorption. (6) The total mass in the AAL outflow is M∼2x10⁹ M_☉, assuming a global covering factor (as viewed from the quasar) of ∼10%. (7) The absorbing gas only partially covers the background light source(s) along our line(s) of sight, requiring absorption in small clouds or filaments less than 0.01 pc across. The ratio N_H/n_H implies that the clouds have radial (line-of-sight) thicknesses ≲0.2 pc. These properties might characterize a subclass of AALs that are physically related to quasars but form at large distances. We propose a model for the absorber in which pockets of dense neutral gas are surrounded by larger clouds of generally lower density and higher ionization. This outflowing material might be leftover from a blowout associated with a nuclear starburst, the onset of quasar activity, or a past broad absorption line (BAL) wind phase.