Probing the Galactic Halo along the 3C 273 Sight Line Using IUE

Abstract

High-resolution spectra of the QSO 3C 273 were obtained in 1989 and added to two spectra recorded in 1982. The co-added spectra represent 600,000 s of integration at a resolution of 30 km s^-1^ from 1200 to 2000 A. The line of sight passes through the Virgo Cluster the entire halo of the Milky Way, at Galactic latitude b = 64^deg^, and foreground X-ray- emitting material from local disturbed gas. The observed equivalent width of Galactic C IV is greater than the equivalent width of C II, a situation that is uncommon in local gas but is often found in QSO absorption line systems. The lines of C IV, Al III, and Si IV may arise in an extended halo or may be associated with local disturbed gas in a radio loop. The remaining detected species (H I, C II, Si II) arise predominately from the local gas. Most of the gas is probably within 5 kpc, but no firm conclusion is reached. Possible detection of interstellar absorption due to the Virgo Cluster is discussed.