The HST Quasar Absorption Line Key Project XII. 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 ata redshift of z_abs=0.695 in the spectrum of the z_em=1.052 radio-quiet quasarPG 2302+039. Broad absorption with FWHM from 3,000 to 5,000 km/s is detectedfrom C IV, N V, and O VI in HST Faint Object Spectrograph spectra of thequasar. A narrow line system (FWHM approximately 250 km/s) at z_abs=0.7016 isresolved from the broad blend and includes absorption by Ly-alpha and the C IV,N V, and O VI doublets. No absorption by low-ionization metal species (e.g. SiII and Mg II) is detected in the HST or ground-based spectra for either thebroad or the narrow system. The centroids of the broad system lines aredisplaced by approximately 56,000 km/s to the blue of the quasar's broademission lines. The reddest extent of the broad line absorption is more than50,000 km/s from the quasar. The properties of this system are unprecedentedwhether it is an intervening or an ejected system.