Evolution of the Abundance of CO, O 2 , and Dust in the Early Universe

Abstract

We present a general set of calculations describing the chemical evolution of young massive galaxies and predict the evolution of the CO, O2, and dust abundances as a function of age and metallicity. Over a wide range of input parameters, the models predict that (1) the total mass in gaseous metals peaks at early epochs (z ~ 1-3) when approximately half the total baryonic mass is in stars and half is in gas; (2) at its extreme, the mass of gaseous metals ranges from a few to more than 10 times larger than the mass of gaseous metals at the current epoch; (3) owing to the larger O/C ratios in chemically young systems, the O2/CO ratio may be of order unity within dark molecular clouds at early cosmological epochs; and (4) at early epochs, the global volume-weighted O2/CO abundance ratios corrected for photodissociation are lowered significantly compared to the dark cloud solutions owing to the lower metallicities and the higher UV fields. For a variety of models, we calculate the evolution of the mass of CO, O2, and dust. We also compute the CO(1 ? 0) and O2(1, 1 ? 1, 0) line intensities and the thermal dust emission as a function of redshift. The model calculations suggest that both redshifted thermal dust emission and CO line emission will be easily observable in young massive galaxies with the next generation of millimeter- and submillimeter-wavelength telescopes. Although more challenging, the O2 lines may be observable in chemically young galaxies. Even though molecular oxygen has yet to be observed outside the solar system, and hence is much less abundant than CO in the Milky Way, the models indicate that O2 may be significantly more abundant in the early stages of galaxy evolution.