Abstract
Context. A powerful tool with which to probe the gas content at high redshift is the [C II] 158 μm submillimetre emission line, which, due to its low excitation potential and luminous emission, is considered a possible direct tracer of star forming gas.
Aims. In this work, we investigate the origin, evolution, and environmental dependencies of the [C II] 158 μm emission line, as well as its expected correlation with the stellar mass and star formation activity of the high-redshift galaxies observed by JWST.
Methods. We use a set of state-of-the-art cold-gas hydrodynamic simulations (COLDSIM) with fully coupled time-dependent atomic and molecular non-equilibrium chemistry and self-consistent [C II] emission from metal-enriched gas. We accurately track the evolution of H I, H II, and H2 in a cosmological context and predict both global and galaxy-based [C II] properties.
Results. For the first time, we predict the cosmic mass density evolution of [C II] and find that it is in good agreement with new measurements at redshift z = 6 from high-resolution optical quasar spectroscopy. We find a correlation between [C II] luminosity, L[C II], and stellar mass, which is consistent with results from ALMA high-redshift large programs. We predict a redshift evolution in the relation between L[C II] and the star formation rate (SFR), and provide a fit to relate L[C II] to SFR, which can be adopted as a more accurate alternative to the currently used linear relation.
Conclusions. Our findings provide physical grounds on which to interpret high-redshift detections in contemporary and future observations, such as the ones performed by ALMA and JWST, and to advance our knowledge of structure formation at early times.