Clues on the Missing Sources of Reionization from Self-consistent Modeling of Milky Way and Dwarf Galaxy Globular Clusters

Abstract

Globular clusters are unique tracers of ancient star formation. We determine the formation efficiencies of globular clusters across cosmic time by modeling the formation and dynamical evolution of the globular cluster population of a Milky Way type galaxy in hierarchical cosmology, using the merger tree from the Via Lactea II simulation. All of the models are constrained to reproduce the observed specific frequency and initial mass function of globular clusters in isolated dwarfs. Globular cluster orbits are then computed in a time varying gravitational potential after they are either accreted from a satellite halo or formed in situ, within the Milky Way halo. We find that the Galactocentric distances and metallicity distribution of globular clusters are very sensitive to the formation efficiencies of globular clusters as a function of redshift and halo mass. Our most accurate models reveal two distinct peaks in the globular cluster formation efficiency at z~2 and z~7-12 and prefer a formation efficiency that is mildly increasing with decreasing halo mass, the opposite of what expected for feedback-regulated star formation. This model accurately reproduces the positions, velocities, mass function, metallicity distribution, and age distribution of globular clusters in the Milky Way and predicts that ~ 40% formed in situ, within the Milky Way halo, while the other ~ 60% were accreted from about 20 satellite dwarf galaxies with Vc > 30 km/s, and about 29% or all globular clusters formed at redshifts z > 7. These results further strengthen the notion that globular cluster formation was an important mode of star formation in high-redshift galaxies and likely played a significant role in the reionization of the intergalactic medium

22 pages, 17 figures, submitted to MNRAS, comments welcome

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• Dark Matter Halos in Galaxies and Globular Cluster Populations. II: Metallicity and Morphology
• A Common Origin for Globular Clusters and Ultra-faint Dwarfs in Simulations of the First Galaxies
• New Methods for Identifying Lyman Continuum Leakers and Reionization-Epoch Analogues
• Simulating Star Clusters Across Cosmic Time: II. Escape Fraction of Ionizing Photons from Molecular Clouds
• Evolution of star cluster systems in isolated galaxies: first results from direct $N$-body simulations
• Search Instructions for Globular Clusters in Formation at High Redshifts
• The evolution of the UV luminosity function of globular clusters in the E-MOSAICS simulations
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