Predictions of the L [C ii] –SFR and [Cii] Luminosity Function at the Epoch of Reionization

Abstract

We present the first predictions for the L [C ii ] –SFR relation and [C ii ] luminosity function (LF) in the epoch of reionization (EOR) based on cosmological hydrodynamics simulations using the simba suite plus radiative transfer calculations via sígame . The sample consists of 11,137 galaxies covering halo mass log M halo  ∈ [9, 12.4] M ⊙ , star formation rate SFR ∈ [0.01, 330] M ⊙ yr −1 , and metallicity 〈 Z gas 〉 SFR  ∈ [0.1, 1.9] Z ⊙ . The simulated L [C ii ] –SFR relation is consistent with the range observed, but with a spread of ≃0.3 dex at the high end of SFR (>100 M ⊙ yr −1 ) and ≃0.6 dex at the lower end, and there is tension between our predictions and the values of L [C ii ] above 10 8.5 L ⊙ observed in some galaxies reported in the literature. The scatter in the L [C ii ] –SFR relation is mostly driven by galaxy properties, such that at a given SFR galaxies with higher molecular mass and metallicity have higher L [C ii ] . The [C ii ] LF predicted by simba is consistent with the upper limits placed by the only existing untargeted flux-limited [C ii ] survey at the EOR and those predicted by semianalytic models. We compare our results with existing models and discuss the differences responsible for the discrepant slopes in the L [C ii ] –SFR relation.