The new era of Lyman alpha emitters (LAEs): Typical star formation histories of LAEs in the ILLUSTRIS simulation

Abstract

This work seeks to understand the nature of Lyman-alpha emitting galaxies in a cosmological context by analyzing their star-formation histories in the IllustrisTNG100 simulation, applying a recent selection criterion. The sample at z = 2.0 includes 6051 Lyman-alpha emitters, classified into four classes (35%, 33%, 21%, and 11%) using KMeans, an unsupervised machine-learning clustering method. The first class reproduces the typical star-formation history, characterized by the most intense star formation at the time of observation. The remaining classes exhibit atypical star-formation histories, with bursts occurring 0.3, 0.7, and 1.3 Gyr before the time of observation. The first class corresponds to galaxies with lower mass, Lyman-alpha luminosity, and total star-formation rate. We conclude that the classical definition of Lyman-alpha emitting galaxies-low mass, low dust content, and a single dominant burst-remains the most representative population (35% of the total sample), although other classes account for the remaining 65% of the cosmological sample.