Title: Highly ionized gas absorption in the disk and halo toward HD 167756 at 3.5 kilometers per second resolution
Abstract: view Abstract Citations (50) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Highly Ionized Gas Absorption in the Disk and Halo toward HD 167756 at 3.5 Kilometers per Second Resolution Savage, Blair D. ; Sembach, Kenneth R. ; Cardelli, Jason A. Abstract High-resolution spectra of interstellar Si IV, C IV, and N V absorption lines along the 4 kpc path to the inner Galaxy star HD 167756 at z = -0.85 kpc are presented. The spectra were obtained with the echelle mode of Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) and have signal-to-noise ratios ranging from 23 to 38. The high resolution of the measurements full width at half maximum (FWHM = 3.5 km/s) results in fully resolved line profiles for the highly ionized gas absorption. The measurements provide information on the column density per unit velocity, N(v), as a function of velocity for Si IV, C IV, and N V. The C IV and N V profiles extend from -70 to +70 km/s, while the Si IV profiles extend from -40 to +70 km/s. The integrated logarithmic column densities are long N(Si IV) = 13.09 +/- 0.02, log N(C IV) = 13.83 +/- 0.02, and log N(N V) = 13.56 +/- 0.03. The N V profile is broad, asymmetric, and featureless, while the Si IV profile contains narrow absorption components near VLSR = -19, 0, +20, and +52 km/s with Doppler spread parameters, b about = 10-12 km/s. The C IV profile contains both broad and narrow structure. The high ion feature near +52 km/s is also detected in the low-ionization lines of Ca II, O I, Si II, and Fe II. The other narrow Si IV and C IV components occur within several km/s of components seen in low-ionization species. The sight line contains at least two types of highly ionized gas. One type gives rise to a broad N V profile, and the other results in the more structured Si IV profile. The C IV profile contains contributions from both types of highly ionized gas. The broad but asymmetric N V profile is well represented by a large Galactic scale height gas which is participating in Galactic rotation and has a combination of thermal and turbulent broadening with btot about = 42 km/s. The C IV to N V abundance ratio of 1.0 +/- 0.3 for the gas implies T about 1.6 x 105 K or about 8 x 105 K if the gas is in collisional ionization equilibrium and has a solar carbon to nitrogen abundance ratio. This absorption may be associated with cooling hot gas situated in Galactic shells and supershells along the sight line. The gas producing the narrow Si IV and C IV absorption components has line widths that are compatible with origins in conductive interfaces between the warm and hot interstellar medium. Kinematic flows associated with the photoionized edges of clouds might also produce Si IV and C IV lines with Doppler spread parameters similar to those observed, but the C IV to Si IV ratio in this gas is 3.5, which leads us to favor the conductive interface interpretation. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173552 Bibcode: 1994ApJ...420..183S Keywords: Absorption Spectra; Disk Galaxies; Galactic Halos; Interstellar Matter; Ionized Gases; Photoionization; Abundance; Galactic Rotation; Signal To Noise Ratios; Stellar Spectra; Ultraviolet Astronomy; Astrophysics; GALAXY: HALO; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 167756; ISM: ABUNDANCES; ULTRAVIOLET: ISM full text sources ADS | data products SIMBAD (3) MAST (1) ESA (1)
Publication Year: 1994
Publication Date: 1994-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 28
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