Damped Lyman alpha systems or Damped Lyman alpha absorption systems is a term used by
astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
s for concentrations of neutral
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas that are detected in the
spectra of
quasars – a class of distant
Active Galactic Nuclei
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...
. They are defined to be systems where the column density (density projected along the line of sight to the quasar) of hydrogen is larger than 2 x 10
20 atoms/cm
2.
The observed spectra consist of neutral hydrogen
Lyman alpha
The Lyman-alpha line, typically denoted by Ly-α, is a spectral line of hydrogen (or, more generally, of any one-electron atom) in the Lyman series. It is emitted when the atomic electron transitions from an ''n'' = 2 orbital to the gr ...
absorption lines which are broadened by
radiation damping
Radiation damping in accelerator physics is a way of reducing the beam emittance of a high-velocity charged particle beam by synchrotron radiation.
The two main ways of using radiation damping to reduce the emittance of a particle beam are the us ...
.
These systems can be observed in quantity at relatively high
redshifts of 2–4, when they contained most of the neutral hydrogen in the universe.
They are believed to be associated with the early stages of
galaxy formation, as the high neutral hydrogen column densities of DLAs are also typical of sightlines in the
Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
, and other nearby galaxies. Since they are observed in absorption rather than emissions by their stars, they offer the opportunity to study the dynamics of the gas in early galaxies directly.
See also
*
Lyman-alpha blob
In astronomy, a Lyman-alpha blob (LAB) is a huge concentration of a gas emitting the Lyman-alpha emission line. LABs are some of the largest known individual objects in the Universe. Some of these gaseous structures are more than 400,000 light ...
*
Lyman-alpha emitter
A Lyman-alpha emitter (LAE) is a type of distant galaxy that emits Lyman-alpha radiation from neutral hydrogen.
Most known LAEs are extremely distant, and because of the finite travel time of light they provide glimpses into the history of the un ...
*
Lyman-alpha forest
The Lyman-alpha line, typically denoted by Ly-α, is a spectral line of hydrogen (or, more generally, of any one-electron atom) in the Lyman series. It is emitted when the atomic electron transitions from an ''n'' = 2 orbital to the gr ...
*
Lyman-break galaxy Lyman-break galaxies are star-forming galaxies at high redshift that are selected using the differing appearance of the galaxy in several imaging filters due to the position of the Lyman limit. The technique has primarily been used to select gal ...
References
Physical cosmology
Astronomical spectroscopy
Intergalactic media
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