A STUDY OF ULTRAVIOLET-ABSORPTION LINES THROUGH THE COMPLETE GALACTIC HALO BY THE ANALYSIS OF HST FAINT OBJECT SPECTROGRAPH SPECTRA OF ACTIVE GALACTIC NUCLEI .1.

The ultraviolet (1150-2850 Angstrom) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, PG 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II > 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.