THE HUBBLE SPACE TELESCOPE QUASAR ABSORPTION LINE KEY PROJECT: THE UNUSUAL ABSORPTION- LINE SYSTEM IN THE SPECTRUM OF PG 2302 + 029—EJECTED OR INTERVENING?

摘要

We report the discovery of a high-ionization broad absorption line system at a redshift of z_(abs) = 0.695 in the spectrum of the z_(em)= 1.052 radio-quiet quasar PG 2302 + 029. Broad absorption with FWHM from 3000 to 5000 km s~(-1) is detected from C IV, N V, and O VI in Hubble Space Telescope (HST) Faint Object Spectrograph spectra of the quasar. A narrow-line system (FWHM ～250 km s~(-1)) at z_(abs) = 0.7016 is resolved from the broad blend and includes absorption by Lyα and the C IV, N V, and O VI doublets. No absorption by low-ionization metal species (e.g., Si II and Mg II) is detected in the HST or ground-based spectra for either the broad or the narrow system. The centroids of the broad system lines are displaced by ～56,000 km s~(-1) to the blue of the quasar's broad emission lines. The reddest extent of the broad-line absorption is more than 50,000 km s~(-1) from the quasar. The properties of this system are unprecedented, whether it is an intervening or an ejected system.