2020MNRAS.495L..22V

We present a novel method to simultaneously characterize the star formation law and the interstellar medium properties of galaxies in the epoch of reionization (EoR) through the combination of [C II] 158 µm (and its known relation with star formation rate) and C III] λ1909 Å emission line data. The method, based on a Markov chain Monte Carlo algorithm, allows us to determine the target galaxy average density, n, gas metallicity, Z, and 'burstiness' parameter, κ_s, quantifying deviations from the Kennicutt-Schmidt relation. As an application, we consider COS-3018 (z = 6.854), the only EoR Lyman Break Galaxy so far detected in both [C II] and C III]. We show that COS-3018 is a moderate starburst (κ_s ≃ 3), with Z ~0.4 Z_☉, and n ~500 cm^–3. Our method will be optimally applied to joint ALMA and James Webb Space Telescope targets.