High-Redshift Supernovae and the Metal-Poor Halo Stars: Signatures of the First Generation of Galaxies

Abstract

Recent evidence on the metal content of the high-redshift Lyman alpha forest seen in quasar spectra suggests that an early generation of galaxies enriched the intergalactic medium (IGM) at z ~ 5. We calculate the number of supernovae that need to have taken place to produce the observed metallicity. The progenitor stars of the supernovae should have emitted $\sim 20$ ionizing photons for each baryon in the universe, i.e., more than enough to ionize the IGM. We calculate that the rate of these supernovae is such that about one of them should be observable at any time per square arc minute. Their fluxes are, of course, extremely faint: at z=5, the peak magnitude should be K=27 with a duration of ~ 1 year. However, these supernovae should still be the brightest objects in the universe beyond some redshift, because the earliest galaxies should form before quasars and they should have very low mass, so their luminosities should be much lower than that of a supernova. We also show that, under the assumption of a standard initial mass function, a significant fraction of the stars in the Galactic halo should have formed in the early galaxies that reionized and enriched the IGM, and which later must have merged with our Galaxy. These stars should have a more extended radial distribution than the observed halo stars.