On the distance from quasars to absorbing clouds.
Abstract
A lower limit to the distance from a quasar to an absorbing cloud is derived for the case where the quasar spectrum shows resonance absorption lines but not lines from excited fine-structure levels. As first discussed by Bahcall (1967), these limits arise from the requirement that the rate of UV radiative excitation from the continuum emission of the quasar be small. Previous calculations, which assumed that the clouds were optically thin in the lines, found that the clouds must be at least a kiloparsec away from the quasar. Distance limits as derived for the case where the clouds are optically thick, and it is found that the clouds may be within a few parsecs of the quasar.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1979
- DOI:
- 10.1086/182879
- Bibcode:
- 1979ApJ...227L.113S
- Keywords:
-
- Astronomical Spectroscopy;
- Electromagnetic Absorption;
- Interstellar Extinction;
- Quasars;
- Absorption Spectra;
- Clouds;
- Line Spectra;
- Optical Thickness;
- Ultraviolet Astronomy;
- Astrophysics;
- Absorption Lines:Quasars