Metal Enrichment and Reionization Constraints on Early Star Formation
  The epoch of reionization and formation of first stars are inter-linked
topics that are of considerable interest. We use a simplified approach for
studying formation of stars in collapsed haloes, and the resulting ionization
of the inter-galactic medium (IGM). We consider a set of LCDM models allowed by
observations of CMB temperature and polarization anisotropies for this study.
We constrain parameters related to star formation with the help of
observations. We constrain subsets of these parameters independently by using
the observed metallicity of the inter-galactic medium at z ~ 5 and the
requirement that the Thomson scattering optical depth due to an ionized IGM as
determined for the model from CMB observations be reproduced. We consider a
range of initial metalicities for star forming gas, and some variations of the
initial mass function of stars. We find that a "normal" initial mass function
(IMF) may satisfy these two constraints with a raised efficiency of star
formation as compared to that seen in the local universe. Observations require
a significant fraction of metals to escape from haloes to the IGM. We can also
place constraints on the ratio of escape fraction for metals and ionizing
photons, we find that this ratio is of order unity for most models. This
highlights the importance of using the constraints arising from enrichment of
the inter-galactic medium. (Abridged)
