Time‐variable Intrinsic Absorption Lines in the Quasi‐stellar Object Q2343+125

Abstract

We discuss high-resolution Keck Observatory spectra of an intrinsic absorption-line system at redshift za ≈ 2.24 in the radio-quiet QSO Q2343+125 (ze = 2.515). The absorber's physical relationship to the QSO is confirmed by time-variable line strengths and partial line-of-sight coverage of the QSO continuum source. The N V, C IV, and Si IV doublets varied in unison by factors of 4 in less than 0.3 yr in the QSO rest frame. The resolved C IV doublet ratios show that the absorber occults 20% of the QSO continuum source; therefore, the absorbing clouds are likely to have characteristic sizes less than 0.01 pc. There is evidence for smaller coverage fractions when the lines were weaker, which could explain the line-strength changes. Lower ionization species such as C II and Si II are not detected. The Lyα line at za ≈ 2.24 is contaminated by the dense forest of cosmologically intervening absorption lines, but also appears to be weak or absent. The large uncertainties in the H I column prevent reliable constraints on the metal abundances. The za ≈ 2.24 lines clearly form in high-velocity ejecta from the QSO. The line profiles are smooth and rounded, with FWHM ~ 400 km s-1 and centroids shifted -24,000 km s-1 from the QSO emission redshift. Several narrow-line systems are present inside the broader absorption profiles, but they did not vary in strength and may be due to intervening gas. The large-amplitude variability, low coverage fractions, and large ratio of centroid to FWHM velocities imply different outflow properties than those inferred from the broad absorption lines (BALs) in other sources. Nonetheless, the ejecta identified by the za ≈ 2.24 absorber could be related to the BAL phenomenon and could be ubiquitous in QSOs if the gas subtends a small fraction of the sky as seen from the emission source(s).