Ultraviolet absorption by highly ionized halo gas near the galactic center.

Abstract

As part of a program to survey highly ionized gas in the Milky Way disk and halo, the authors have obtained high-resolution IUE far-UV spectra of 12 stars at galactocentric distances less than 6 kpc. The stars are 0.7 - 2.2 kpc away from the plane. Most of the spectra contain exceedingly strong and broad interstellar absorption lines of weakly and highly ionized atoms. In addition to the normally strong lines of Si IV and C IV, strong interstellar N V lines have been detected in the spectra of eight stars. Contrary to expectations, there is no evidence in the data that the halo of the inner Galaxy (R_g < 6 kpc) differs substantially from the halo of the outer Galaxy (R_g > 6 kpc). The detection of N V absorption toward eight stars provides an important new constraint on models for the origin of galactic halo gas.