The Consequences of the Cosmic Star Formation Rate: X-Ray Number Counts

We discuss the observable consequences for the detection of galaxies in the X-ray bandpass resulting from a peak in the cosmic star formation rate at a redshift greater than 1. Following N. White and P. Ghosh, we assume a large evolution in the X-ray/ B luminosity ratio at z ~ 0.5-1.5 resulting from the X-ray binaries that have evolved from stars formed at z > 1-2. Using the Hubble Deep Field-North (HDF-N) redshift survey data and the locally observed X-ray/ B luminosity ratio as a guide, we estimate a median X-ray flux (2-10 keV) on the order of 8 × 10 -18 ergs cm -2 s -1 for galaxies in the HDF-N, which is consistent with a signal derived from a recent stacking analysis of the HDF-N Chandra data by N. Brandt and coworkers. We also predict the number counts in deep X-ray surveys expected from normal galaxies at high redshift.