Editing Lyman-alpha forest (section)

==Use as a tool in astrophysics==

The Lyman-alpha forest is an important probe of the [[Outer space#Intergalactic space|intergalactic medium]] and can be used to determine the frequency and density of clouds containing neutral [[hydrogen]], as well as their temperature. Searching for lines from other elements like [[helium]], [[carbon]] and [[silicon]] (matching in [[redshift]]), the abundance of heavier elements in the clouds can also be studied. A cloud with a high column density of neutral hydrogen will show typical [[damping wings]] around the line and is referred to as a [[damped Lyman-alpha system]].

For quasars at higher redshift the number of lines in the forest is higher, until at a redshift of about 6, where there is so much neutral hydrogen in the intergalactic medium that the forest turns into a [[Gunn–Peterson trough]]. This shows the end of the [[reionization]] of the universe.

The Lyman-alpha forest observations can be used to constrain cosmological models.<ref>{{cite conference
 | author = Weinberg, D. H.
 | s2cid = 118868536
 | display-authors = etal
 | title = The Lyman-α Forest as a Cosmological Tool
 | book-title = The Emergence of Cosmic Structure: Thirteenth Astrophysics Conference
 |date=May 2003
 | arxiv=astro-ph/0301186
 | series = AIP Conference Series
 | volume = 666
 | editor = S. H. Holt
 | editor2 = C. S. Reynolds
 | pages = 157–169
 | doi = 10.1063/1.1581786
|isbn=0-7354-0128-4
 | bibcode = 2003AIPC..666..157W
 }}</ref> They can also be used to constrain the properties of [[dark matter]], such as the dark matter free streaming scale, which for thermal relic dark matter models is closely related to the dark matter particle mass.