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-ionisation AALs of SiII or CII 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 $\sim$0 to
$\sim$1150 km s$^{-1}$ at distance $\sim$5.7 kpc from the quasar. The range of
ions detected, up to NeVIII, indicates a wide range of densities from $\sim$4
to $\sim$2500 cm$^{-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 suggests 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 $\sim$1900 to
$\sim$3000 km s$^{-1}$. Some of them also appear to have a range of densities
based on the range of ions detected, including MgI $\lambda$2853 in Q0105+061.
However, the absence of excited-state AALs yields only upper limits on their
gas densities ($\lesssim150$ cm$^{-3}$) and large minimum distances
($\gtrsim$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.
