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Intervening O vi Quasar Absorption Systems at Low Redshift: A Significant Baryon Reservoir.
The Astrophysical Journal
|May 2, 2000
Summary
This study reveals a high number density of O vi absorption systems in the low-redshift intergalactic medium. These systems suggest a significant cosmic baryonic mass density, comparable to stars and gas in galaxies.
Area of Science:
- Astronomy and Astrophysics
- Cosmology
- Intergalactic Medium
Background:
- Quasars are active galactic nuclei emitting intense radiation across the electromagnetic spectrum.
- Far-UV spectroscopy allows the study of absorption lines from various ions in the intergalactic medium.
- O vi absorption lines are crucial tracers of highly ionized gas in the universe.
Purpose of the Study:
- To investigate the properties and number density of O vi absorption systems in the low-redshift intergalactic medium.
- To estimate the cosmological mass density of gas traced by O vi absorbers.
- To compare the mass density of O vi systems with other baryonic components in the universe.
Main Methods:
- Far-UV echelle spectroscopy of the radio-quiet quasar H1821+643 using the Space Telescope Imaging Spectrograph (STIS).
- Analysis of O vi, Si iii, and H i Lyman series absorption lines to identify and characterize absorption systems.
- Measurement of absorption line properties, including redshift, velocity centroids, b-values, and column densities.
Main Results:
- Detection of four definite and one probable O vi absorption systems at redshifts between 0.15 and 0.27.
- Identification of a multiphase absorption system at zabs=0.22497 with multiple components in Si iii, O vi, and H i.
- Remarkably high number density of O vi absorbers (dN/dz ≈ 48), implying a lower limit of >17 in the low-redshift intergalactic medium.
- Estimated cosmological mass density of O vi systems (Ωb(O vi)) is at least 0.0008 h-175, and potentially as high as 0.004 h-175.
Conclusions:
- The number density of O vi absorbers is significantly high, indicating a substantial population of ionized gas in the low-redshift intergalactic medium.
- The cosmological mass density inferred from O vi systems is comparable to that of stars, cool gas in galaxies, and hot gas in galaxy clusters.
- O vi absorption systems represent a significant, previously underestimated, component of the baryonic matter in the universe.
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