High-resolution spectroscopy of the Z = 1.79 absorption-line system toward B2 1225 + 317

The authors observed several species of the absorption line system at z = 1.79 toward the bright quasar B2 1225+317 (zem = 2.22, mv = 15.9) with the echelle spectrograph on the MMT, at a resolution of 10 km s⁻¹. The absorption-line profiles differ from species to species, with some velocity components showing absorption in both low-ionization species (Mg I, Mg II, Fe II, Si II, C II) and high-ionization species (C IV and Si IV), while other components show absorption only in C IV and Si IV. The relative column densities of Si II, Mg II, Zn II, Fe II, and H I are consistent with the local interstellar medium values. The properties of the radiation field longward of the Lyman limit are investigated.