On the uncertainties of state-of-the-art models designed for interpreting galaxy spectra: preparing for the JWST era.

Recent spectroscopy of a small sample of galaxies at z~6-7 has revealed surprisingly bright emission in [C III] 1907 + C III] 1909, He II 1640, and/or C IV 1548, 155 lines. This suggests that these lines will be critical for studying galaxy properties at z>6, in regimes where H I 1216 (Lyman-alpha), which is traditionally used for this purpose, is severely attenuated by the IGM. 

JWST NIRSpec will be able to detect the rest-frame UV of galaxies located at redshifts z~10-15. This spectral range will include the contributions of metal-free massive stars, H II regions, shocks, and accreting black holes. There will be at least two challenges in interpreting these data: a) disentangling the contributions to UV lines of the above various sources, and b) if the integrated spectrum is dominated by stars + nebulae, selecting the best flavour of massive-star evolution at extremely low metallicity.

I will explain how we are using detailed HST observations of nearby targets and state-of-the-art modelling and fitting techniques in order to address some of these challenges.