COLDSIM predictions of [C II] emission in primordial galaxies
Benedetta Casavecchia, Umberto Maio, Céline Péroux, B. Ciardi
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 (C OLD SIM) 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 H 2 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.