Detection of the First Star Clusters With NGST

We calculate the observable signatures of the first generation of stars at high redshift (5<z<100). To determine the cosmic star-formation history, we use an extension of the Press-Schechter formalism for Cold Dark Matter (CDM) cosmologies that incorporates gas pressure. We calibrate the fraction of gas converted into stars to be 6% so as to reproduce the 1% solar C/H ratio observed in the intergalactic medium (IGM) at z=3. With this star-formation efficiency, we find that NGST would be able to image more than 10^4 star clusters from high redshifts (z>10) within its 4'x4' field of view. If stars occupy a region comparable to the virial radius of the cluster, then 1% of these clusters could be resolved. We calculate the expected number-flux relation and angular size distribution for these early star clusters. We also describe the reionization of the IGM due to the first generation of stars, and the consequent damping of the CMB anisotropies on small angular scales. This damping could be detected below 10 degree angular scales by MAP and PLANCK.