2002ApJ...567L..13R

We present a Keck Observatory/Echelle Spectrograph and Imager spectrum of FIRST 074711.2+273904, a K=15.4 quasar with a redshift of 4.11 that is detected by both the Faint Images of the Radio Sky at Twenty cm (FIRST) survey and the Two Micron All Sky Survey (2MASS). The spectrum contains at least 14 independent C IV absorption systems longward of the Lyα forest. These systems are found over a path length of Δz=0.984, constituting one of the highest densities per unit redshift of C IV absorption ever observed. One of the C IV systems is troughlike and resembles a weak broad absorption line (BAL)-type outflow. Two of the C IV are ``associated'' absorption systems with |v|<3000 km.s^–1. Of the 11 remaining systems with v>3000 km.s^–1, eight are either resolved or require multiple discrete systems to fit the line profiles. In addition to C IV absorption, there are two low-ionization Mg II absorption systems, along with two damped Lyα systems, at least one of which may be a C IV system. The overdensity of C IV absorption spans a redshift range of Δz∼1. Superclusters along the line of sight are unlikely to cause an overdensity stretching over such a long redshift path; thus, the absorption may be an example of narrow, high-velocity intrinsic absorption that originates from the quasar. We suggest that this quasar is a member of a transitional class of BAL quasars, where we are just barely seeing the spatial, density, or temporal edge of the BAL-producing region (or period); the multiple high-velocity absorption systems may be the remnants (or precursors) of a stronger BAL outflow. If correct, then some simpler absorption-line complexes in other quasars may also be due to outflowing rather than to intervening material.