Evidence for inhomogeneous reionization in the local Universe from metal-poor globular cluster systems

TL;DR

This study uses the spatial distribution and movement of metal-poor globular clusters around galaxies to estimate the timing of reionization in different environments, aligning with cosmological models and suggesting environmental differences.

Contribution

First attempt to constrain local reionization epoch using globular cluster systems across different galaxy environments in the local Universe.

Findings

Reionization epoch around galaxies estimated at z_reion ≈ 10.5.

Results agree with WMAP and other global reionization estimates.

Evidence suggests reionization completed earlier in low-density environments.

Abstract

Exploiting a fundamental characteristic of galaxy assembly in the {\Lambda}CDM paradigm, the observed spatial biasing and kinematics of metal-poor globular star clusters are used to constrain the local reionization epoch around individual galaxies. Selecting three galaxies located in different environments, the first attempt at constraining the environmental propagation of reionization in the local Universe is carried out. The joint constraint from the three galaxies (z_reion = 10.5^{+1.0}_{-0.9}) agrees remarkably well with the latest WMAP constraint on z_reion for a simple instantaneous reionization model. More importantly, the range of z_reion values found here are consistent with the global range of z_reion estimates from other observations. We furthermore find a 1.7{\sigma} indication that reionization completed in low-density environments before the intergalactic medium in high-density environments was reionized. This is consistent with certain theoretical models that predict that reionization was globally prolonged in duration, with neutral hydrogen pockets surviving in high-density environments, even after the surrounding regions were reionized. More generally, this work provides a useful constraint on the formation history of galaxy stellar halos.