Formation of metal-poor globular clusters in Lyα emitting galaxies in the early universe

Abstract

The size, mass, luminosity, and space density of Lyα emitting (LAE) galaxies observed at intermediate to high redshift agree with expectations for the properties of galaxies that formed metal-poor halo globular clusters (GCs). The low metallicity of these clusters is the result of their formation in low-mass galaxies. Metal-poor GCs could enter spiral galaxies along with their dwarf galaxy hosts, unlike metal-rich GCs, which form in the spirals themselves. Considering an initial GC mass larger than the current mass to account for multiple stellar populations, and considering the additional clusters that are likely to form with massive clusters, we estimate that each GC with a mass today greater than 2 × 105 M ⊙ was likely to have formed among a total stellar mass ≳ 3 × 107 M ⊙, a molecular mass ≳ 109 M ⊙, and 107 to 109 M ⊙ of older stars, depending on the relative gas fraction. The star formation rate would have been several M ⊙yr-1 lasting for 107yr, and the Lyα luminosity would have been ≳ 1042ergs-1. Integrating the LAE galaxy luminosity function above this minimum, considering the average escape probability for Lyα photons (25%), and then dividing by the probability that a dwarf galaxy is observed in the LAE phase (0.4%), we find agreement between the comoving space density of LAEs and the average space density of metal-poor GCs today. The local galaxy WLM, with its early starburst and old GC, could be an LAE remnant that did not get into a galaxy halo because of its remote location. © 2012. The American Astronomical Society. All rights reserved.