Mass Outflow in the Seyfert 1 Galaxy NGC 5548
  We present a study of the intrinsic UV absorption and emission lines in an
historically low-state spectrum of the Seyfert 1 galaxy NGC 5548, which we
obtained in 2004 February at high spatial and spectral resolution with the
Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. We
isolate a component of emission with a width of 680 km/s (FWHM) that arises
from an "intermediate line region" (ILR), similar to the one we discovered in
NGC 4151, at a distance of ~1 pc from the central continuum source. From a
detailed analysis of the five intrinsic absorption components in NGC 5548 and
their behavior over a span of 8 years, we present evidence that most of the UV
absorbers only partially cover the ILR and do not cover an extended region of
UV continuum emission, most likely from hot stars in the circumnuclear region.
We also find that four of the UV absorbers are at much greater distances (>70
pc) than the ILR, and none have sufficient N V or C IV column densities to be
the ILR in absorption. At least a portion of the UV absorption component 3, at
a radial velocity of -530 km/s, is likely responsible for most of the X-ray
absorption, at a distance < 7 pc from the central source. The fact that we see
the ILR in absorption in NGC 4151 and not in NGC 5548 suggests that the ILR is
located at a relatively large polar angle (~45 degrees) with respect to the
narrow-line region outflow axis.
