Observing the first galaxies - a case for an intermediate resolution multi-object IR spectrograph

We present a special science case for an intermediate resolution multi-object IR spectrograph for the VLT. We have constructed new models for massive Population III stars and metal-free stellar populations (see Schaerer 2001). The properties of individual stars and integrated populations, including their ionising fluxes and SEDs are discussed. We also study their dependence on the poorly known IMF and the star formation history. The synthetic spectra are used to simulate spectroscopic observations of the expected emission lines of Pop III galaxies. We show that such an instrument should allow the detection and efficient observations of the first galaxies with the VLT.