Cosmic Histories of Stars , Gas , Heavy Elements , and Dust

We present a set of coupled equations that relate the stellar, gaseous, chemical, and radiation constituents of the universe averaged over the whole galaxy population. Using as input the available data from quasar absorption-line surveys, optical imaging and redshift surveys, and the COBE DIRBE and FIRAS extragalactic infrared background measurements, we obtain solutions for the cosmic histories of stars, interstellar gas, heavy elements, dust, and radiation from stars and dust in galaxies. Our solutions reproduce remarkably well a wide variety of observations that were not used as input. These include the integrated background light from galaxy counts from nearultraviolet to near-infrared wavelengths, the rest-frame optical and near-infrared emissivities at various redshifts from surveys of galaxies, the mid-infrared and far-infrared emissivities of the local universe from the IRAS survey, the mean abundance of heavy elements at various epochs from surveys of damped Lyman-alpha systems, and the global star formation rates at several redshifts from Hα surveys and submillimeter observations. The chemical enrichment history of the intergalactic medium implied by our models is also consistent with the observed mean metal content of the Lyman-alpha forest at high redshifts. We find that the dust associated with star forming regions is highly inhomogeneous and absorbs a significant fraction of starlight, with only 41− 46% of galaxy light in the extragalactic optical background and the remaining 59− 54% reprocessed by dust into the cosmic infrared background. The solutions presented here provide an intriguing picture of the cosmic mean history of galaxies over much of the Hubble time. In particular, the process of galaxy formation appears to have undergone an early period of substantial inflow to assemble interstellar gas at z ∼> 3, a subsequent period of intense star formation and chemical enrichment at 1 ∼< z ∼< 3, and a recent period of rapid decline in the gas content, star formation rate, optical stellar emissivity, and infrared dust emission at z ∼< 1. Subject headings: cosmology: diffuse radiation — galaxies: evolution — quasars: absorption lines — infrared: galaxies