Illuminating the CO-Dark Reservoir

Stars form in giant clouds comprised of molecular gas (H_2) and yet we have not quantified the amount of molecular gas there is in the Universe. Historically, we’ve used carbon monoxide (CO) rotational transition lines as a tracer molecule given H_2 is difficult to observe in hospitable conditions for star formation. Despite its accessibility, CO is easily destroyed by ultraviolet radiation and cosmic rays this way leaving a fraction of the molecular gas unaccounted for through the conventional techniques, namely “CO-dark”. Using cosmological simulations, coupled with thermal, radiative, and chemical equilibrium models for the interstellar medium, we will develop the first ever theoretical model for the fraction of molecular gas across the cosmic time that is currently invisible via traditional CO surveys, and quantify how this gas may be observable.