Bulletin of the Astronomical Society of India
Pushpa Khare*
CSIR Emeritus Scientist, IUCAA, Pune, India
Received: 10th March 2013 | Accepted: 29 March 2013
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Quasar spectra, apart from showing the broad, redshifted emission lines, often show narrow as well as broad absorption lines. The presence of absorption lines has been known since shortly after the discovery of these objects. The spectrum of a single quasar can have more than one group of absorption lines, termed absorption line systems, each system having its characteristic redshift. Most of these systems are believed to be produced by galactic or intergalactic clouds, while those having redshifts close to that of the quasar may be produced by material intrinsic to the quasar. These systems thus offer a sensitive probe to understand the evolutionary history of the Universe over 90% of its age as well as the quasar environment. In recent times, the commissioning of large telescopes, high resolution spectrographs, space telescopes, large sky digital surveys and progress in hydro-simulations have resulted in rapid progress in this field. In this article, I will summarize some of our current understanding of these systems and the information that has been obtained about various aspects of the Universe from their study.
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Keywords : quasars: absorption lines – quasars: general – intergalactic medium