Globular Clusters at High Redshift

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 nanojansky 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 10⁷ per square degree at 1 nJy (m_AB = 31.4 mag) in bands around 4 μm. Such high sky densities begin to present a confusion problem at these wavelengths to diffraction-limited 6 m class telescopes. These starlike, 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'' 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.