The gaseous environments of quasars: associate absorption lines with density and distance constraints

Associated absorption lines (AALs) in quasar spectra are valuable probes of the gas kinematics and physical conditions in quasar environments. The host galaxies are by definition in an active evolution stage that might involve large-scale blowouts and/or cold-mode accretion (infall) from the intergalactic medium (IGM). We discuss rest-frame UV spectra of four redshift 2–3 quasars selected to have low-ionization AALs of Si II or C II that place unique density and distance constraints on the absorbers. Our analysis of the AALs yields the following results. One of the quasars, Q0119−046, has a rich complex of 11 AAL systems that appear to be infalling at measured speeds from ∼0 to ∼1150 s^(−1) at distance ∼5.7 kpc from the quasar. The range of ions detected, up to Ne VIII, indicates a wide range of densities from ∼4 to ∼2500 cm^(−3). Partial covering the quasar emission source requires cloud sizes <1 pc and possibly <0.01 pc. The short dissipation times of these small clouds suggest that they are created in situ at their observed location, perhaps as dense condensations in cold-mode accreting gas from IGM. The AALs in the other three quasars have outflow speeds from ∼1900 to ∼3000  s^(−1). Some of them also appear to have a range of densities based on the range of ions detected, including Mg I λ2853 in Q0105+061. However, the absence of excited-state AALs yields only upper limits on their gas densities (≲150 cm^(−3)) and large minimum distances (≳40 kpc) from the quasars. These AALs might represent highly extended quasar-driven outflows, although their actual physical relationships to the quasars cannot be established.