IUE Observations of Highly Ionized Gas toward Distant Stars in the Milky Way

Abstract

Combined high-dispersion IUE spectra of interstellar Si IV, C, IV, and N V absorption along distnat lines toward early type stars in the Galactic disk and low halo are discussed. The highly ionized species have complex profiles and exhibit stronger absorption toward distant low latitude stars than toward high latitude stars. Absorption along low latitude directions is often broadened substantially (up to 100 km S6-1 in some cases) by Galactic rotation. Along these sight lines the Si IV, C IV, and N V profiles are more similar in shape to each other than to those of A1 III, which is a tracer of photoionized interstellar gas. The observed column density ratios of the high ions, <N(C IV)/N(Si IV)>=3.6+/-1.3 and <N(N IV)/N(N V)>=4.6+/-2.7, are similar in widely different regions within the Galaxy. The similarities in the high ion profile shape along individual sight lines and integrated column density ratios along differing sight lines suggest a common origin for these species in collisionally ionized gas associated with a global process such as a Galactic fountain. (SECTION: The Second Hubble Fellows Symposium)