Lyman-alpha emitter

The Lyman-alpha line in most LAEs is thought to be caused by recombination of interstellar hydrogen that is ionized by an ongoing burst of star formation.

This is what portion of the light emitted at the Lyman-alpha line wavelength inside the galaxy actually escapes and will be visible to distant observers.

[3] Evidence now shows strong evolution in the Lyman-alpha escape fraction with redshift, most likely associated with the buildup of dust in the ISM.

[6] Baryonic acoustic oscillations are imprints of sound waves on scales where radiation pressure stabilized the density perturbations against gravitational collapse in the early universe.

They are a good tool because the Lyman-alpha bias, the propensity for galaxies to form in the highest overdensity of the underlying dark matter distribution, can be modeled and accounted for.

A Lyman alpha emitter (left) and an artist's impression of what one might look like if viewed at a relatively close distance (right).