The current and forthcoming observations of large samples of high–redshift galaxies selected according to various photometric and spectroscopic criteria can be interpreted in the context of galaxy formation, by means of models of evolving spectral energy distributions (SEDs). We hereafter present stardust which gives synthetic SEDs from the far UV to the submm wavelength range. These SEDs are d...

Concern about systematic uncertainty in the He abundance as well as the chemical evolution of He leads us to re-examine this important limit. It is shown that with conservative assumptions no more than the equivalent of 4 massless neutrino species are allowed. Even with the most extreme estimates of the astrophysical uncertainties a meaningful limit still exists, less than 5 massless neutrino s...