Abstract
The new Population III models by Schaerer (2002) have been used to derive the observed properties of the first galaxies in terms of the expected magnitudes and colors. The dependence of their properties on the initial mass function and upper mass limit for star formation are studied. The emerging synthetic spectra are used to discuss the implications on different observational features. Strong emission lines, such as Ly α and He II
λ 1640, could easily be detected with a good S/N with near-infrared medium resolution spectrographs, such as EMIR on the GTC. Our simulations aim at exploring possible observational constraints on the formation epoch of the first stars in galaxies.
