Study of interstellar absorption at high galactic latitudes. I. Highly ionized gas

Journal Article · Wed Sep 15 04:00:00 EDT 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160277· OSTI ID:6560582

Pettini, M; West, K A

We present IUE observations of interstellar absorption lines of C IV, Si IV, N V, and Fe II in a sample of 24 distant early-type stars at high galactic latitudes. These data are analyzed together with other published results in order to study the distribution and physical conditions of highly ionized gas in the halo of the Galaxy. C IV and Si IV lines are detected in front of approximately two-thirds of the stars observed. The lines are significantly stronger than those observed in the spectra of disk stars of similar spectral types, and their velocities show no correlation with the velocities of the background stars. Thus, a circumstellar origin for the highly ionized gas seems excluded. We further show that the high ion species detected in the halo are unlikely to arise at the evaporative interfaces of cool clouds responsible for the O VI C IV lines observed in the interstellar medium in the disk, even if the scale height of the clouds were several kiloparsecs. The observed variation of the column densities of C/sup 3 +/ and Si/sup 3 +/ with distance z from the plane is not easily interpreted in terms of a plane-parallel distribution of the gas, but is consistent with a previous suggestion of the existence of a Galactic transition layer between cool gas in the disk and outer halo regions at temperatures greater than those observable with IUE.

• Research Organization: Royal Greenwich Observatory
• OSTI ID: 6560582
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 260:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION SPECTRA
ABUNDANCE
CHARGED PARTICLES
COSMIC GASES
DISTRIBUTION
FLUIDS
FUNCTIONS
GALAXIES
GASES
IONS
MILKY WAY
RADIAL VELOCITY
SPATIAL DISTRIBUTION
SPECTRA
SPECTRAL DENSITY
SPECTRAL FUNCTIONS
ULTRAVIOLET SPECTRA
VELOCITY