Globular Clusters at High Redshift

Abstract

Globular clusters will be present at high redshifts, near the very beginning of the galaxy formation process. Stellar evolution ensures that they will be much more luminous than today. We show that the redshift distribution at nano-Jansky levels should be very broad, extending up to the redshift of formation. A bracketing range of choices for the redshift of formation, spectral energy evolution models and population density evolution, leads to the conclusion that the sky densities should be around 10^7 per square degree at 1nJy (m_AB=31.4 mag) in bands around 4 microns. Such high sky densities begin to present a confusion problem at these wavelengths to diffraction limited 6m class telescopes. These star-like, low metallicity, clusters will be a significant foreground population for ``first light'' object searches. On the other hand they are an exceptionally interesting ``second light'' population in their own right. Depending on the details of galaxy assembly, the clusters will have a noticeable cross-correlation with galaxies on scales of about 20 arcsec, or less, depending on the details of the buildup of galaxy assembly after globular cluster formation. High redshift globular clusters will be an accessible, direct, probe of the earliest stages of the formation of galaxies and the buildup of metals in the universe.