CO LF and molecular gas mass density

ALMA has made significant progress in the study of the cosmic evolution of cold molecular gas. Here, we exploit the ALMACAL survey to address issues relating to small sample sizes and cosmic variance, utilising calibration data from ALMA to compile a statistically significant and essentially unbiased sample of CO-selected galaxies.

By employing a novel statistical approach to emission-line classification using semi-analytical models, we place strong constraints on the CO luminosity function and the cosmic evolution of molecular gas mass density back to z~6. The cosmic molecular gas mass density increases with redshift, peaking around z~1.5, then slowly declines towards higher redshifts by ~1dex. Our findings confirm the key role of molecular gas in fueling star formation.