Lyman-alpha emitters as tracers of the transitioning Universe

TL;DR

This paper reviews how Ly-alpha emitters serve as effective tracers of galaxy evolution across different redshifts, revealing their diverse nature and changing properties over cosmic time.

Contribution

It demonstrates that Ly-alpha emitters are a heterogeneous group reflecting broader galaxy populations, with evolving characteristics from high to low redshift.

Findings

The fraction of ULIRGs among LAEs increases from redshift 3 to 2.

The fraction of AGN among LAEs follows a similar evolutionary trend.

LAEs are not a homogeneous class but represent general star-forming and active galaxies.

Abstract

Of the many ways of detecting high redshift galaxies, the selection of objects due to their redshifted Ly-alpha emission has become one of the most successful. But what types of galaxies are selected in this way? Until recently, Ly-alpha emitters were understood to be small star-forming galaxies, possible building-blocks of larger galaxies. But with increased number of observations of Ly-alpha emitters at lower redshifts, a new picture emerges. Ly-alpha emitters display strong evolution in their properties from higher to lower redshift. It has previously been shown that the fraction of ultra-luminous infrared galaxies (ULIRGs) among the Ly-alpha emitters increases dramatically between redshift three and two. Here, the fraction of AGN among the LAEs is shown to follow a similar evolutionary path. We argue that Ly-alpha emitters are not a homogeneous class of objects, and that the objects selected with this method reflect the general star forming and active galaxy populations at that redshift. Ly-alpha emitters should hence be excellent tracers of galaxy evolution in future simulations and modeling.