Pushpa Khare
Abstract.
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.
Keywords: quasars: absorption lines -- quasars: general -- intergalactic medium
CSIR Emeritus Scientist,
IUCAA, Pune, India