Observations of highly ionized gas in the Galactic halo
K. R. Sembach, B. D. Savage;
ApJS, 1992, 83, 147
ABSTRACT:A sample of high-quality sight lines is studied by means of IUE spectra to study the formation of Si IV, C IV,
and N V in the Galaxy and constrain the mechanisms of halo gas
formation.
High-dispersion IUE spectra are taken for 12 objects to give combined spectra for
studying the halo gas along the sight lines.
N V absorption is reported in 10 of
the sightlines suggesting that hot collisionally ionized gas dominates
the Galactic halo.
Analyses are conducted to derive the Doppler-spread
parameters of the Si IV, C IV, and N V components that are theorized to dominate the
collisionally ionized gas.
The observed column-density ratios of the high ions are
given and shown to be generally constant throughout the Galaxy with no
variation according to the distance of the absorbing gas from the Galactic
plane.
Existing photoionization and collisional models cannot simultaneously
predict the column densities and ratios of Si IV, C IV, and N V.
It is concluded
that the implementation of self-ionization and other mechanisms could
make the models more effective.
KEYWORDS: abundance, galactic halos, interstellar matter, ionized gases, iue, photoionization, data reduction, halos, milky way galaxy, stellar envelopes, ubv spectra
CODE: sembach92