Lyman-alpha emitter

A Lyman-alpha emitter is an astronomical object, usually a distant galaxy, identified by strong emission from hydrogen’s Lyman-alpha spectral line.

Lyman-alpha: The hydrogen spectral line produced when an electron transitions from the first excited state to the ground state. Its emitted photons provide the defining signal used to identify these objects.
High-redshift galaxy: A galaxy observed at large cosmological redshift, seen as it existed in the distant past. Most identified emitters are distant galaxies whose light has been cosmologically shifted.
Himiko (galaxy): A massive, luminous Lyman-alpha-emitting galaxy observed at redshift 6.595. Its extended emission makes it a prominent example of a very distant emitter.
Lyman-break galaxy: A distant galaxy selected through the sharp decrease in its ultraviolet continuum below the Lyman limit. It is selected by continuum dropout rather than strong Lyman-alpha emission.
Lyman-alpha radiative transfer: The transport of Lyman-alpha photons through gas, shaped by repeated resonant scattering and absorption. Repeated scattering alters the line before its photons escape a galaxy.
Reionization: The era when ultraviolet sources transformed much of the intergalactic hydrogen from neutral to ionized. Emitter visibility can reveal how neutral gas changed during this epoch.
CR7 (galaxy): A luminous galaxy at redshift 6.6, identified as a strong Lyman-alpha emitter. Its early interpretation highlighted how emitter spectra can prompt claims about unusual stellar populations.
H-alpha emitter: An astronomical source selected by strong emission in hydrogen’s H-alpha spectral line. It uses another hydrogen line, generally tracing different environments and redshift ranges.
Resonant scattering: Scattering in which a photon is absorbed and re-emitted by a transition matching its energy. It explains why Lyman-alpha photons take complex paths through neutral hydrogen.
Cosmic dawn: The period when the first stars and galaxies began illuminating the universe after the cosmic dark ages. Very distant emitters offer a view of early galaxy formation near this period.

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Galaxy evolutionBroader topic: Its abundance and properties help trace early star-forming galaxy populations.