Forest
Written for the Encyclopedia of Astronomy and Astrophysics
(to be published in 2000 by Mac Millan and the Institute of Physics
Publishing) (astro-ph/000602)
For a PDF version of the article, click
here.
Abstract. We briefly review, at a level appropriate for graduate
students and
non-specialists, the field of quasar absorption lines (QALs). Emphasis
is on the intervening absorbers. We present the anatomy of a quasar
spectrum due to various classes of intervening absorption systems, and
a brief historical review of each absorber class (Lyman-alpha forest and
Lyman limit systems, and metal-line and damped Lyman-alpha absorbers).
We also provide several heuristic examples on how the physical properties
of both the intergalactic medium and the gaseous environments associated
with earlier epoch galaxies can be inferred from QALs. The evolution of
these environments from z = 4 are discussed.
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