The intervening and associated O VI absorption-line systems in the ultraviolet spectrum of H1821+643

Details The intervening and associated O VI absorption-line systems in the ultraviolet spectrum of H1821+643 The intervening and associated O VI absorption-line systems in the ultraviolet spectrum of H1821+643

Feb 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aj....115..436s&link_type=abstract

Astronomical Journal, vol. 115, p. 436

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43

Ultraviolet Spectra, Absorption Spectra, Quasars, Interstellar Matter, Red Shift, Data Reduction, Ionization

Scientific paper

GHRS and FOS ultraviolet spectra of the bright QSO H1821+643 reveal the presence of strong O VI 1031.93, 1037.62 A absorption systems at z(abs) = 0.225 and 0.297, the latter being at the redshift of the QSO itself. Ground-based galaxy redshift measurements by us and others reveal two emission-line galaxies near the redshift of the intervening system at z(abs) = 0.225, suggesting the existence of a galaxy group at this redshift. The intervening O VI absorption system is also detected in H I but is not detected in the lines of Si II, Si IV, C IV, or N V. These ionization characteristics can be explained by a low-density, extended diffuse gas distribution that is photoionized by the metagalactic UV background if the gas has a metallicity of 0.1 times solar. Such a photoionized gas may be associated with the extended halo of the luminous intervening spiral galaxy at a projected distance of 100 h kpc, or with an intragroup medium. Alternatively, the absorption may be produced in hot collisionally ionized halo gas or in a hot intragroup medium. The associated system with z(abs) = 0.297 contains narrow and broad O VI absorption. The narrow absorption, which is also detected in H I, C III, C IV, and Si IV, can be modeled as gas photoionized by H1821+643 with roughly solar abundances. This gas is probably situated close to H1821+643. The broad O VI absorption that is centered at the emission redshift of H1821+643 may represent a weak and narrow example of the broad absorption line phenomena.

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