Origin and distribution of C IV and Si IV ions in the neighboring interstellar medium

We present data on the C IV, Si IV and N absorption lines in 46 distant stars observed with the IUE spectrometer at FWHM resolution of 30 km s-1. Sharp strong Si IV and C IV lines are regularly detected, while N V is not generally observed. Most of the Si IV and C IV lines probably arise in the H II regions surrounding the observed star or near neighbors. A simple analytic theory is given for these contributions, including the effects of ionization by a soft X-ray background. For some of the most distant field stars a photoionized contribution may be ruled out, bur C IV absorption lines are detected. These particular lines are also unusual in that Si IV is not detected and that the lines are shallow and broad. We suggest that in these cases we are detecting contributions from the hot interstellar gas responsible for the O VI absorption lines. We obtain n(C IV) = 4 x 10-9 cm-3, consistent with the predictions of theories of the O VI absorption. An extended (radius > or approx. =100 pc) highly velocity (approx.100 km s-1) feature is observed in the Carina region