Cosmic histories of stars, gas, heavy elements, and dust in galaxies

We investigate a set of coupled equations that relates the stellar, gaseous , chemical, and radiation contents of the universe averaged over the whole population of galaxies. Using as input the available data from quasar absor ption-line surveys, optical imaging and redshift surveys, and the COBE DIRB E and FIRAS extragalactic infrared background measurements, we obtain solut ions for the cosmic histories of stars, interstellar gas, heavy elements, d ust, 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 nea r-ultraviolet to near-infrared wavelengths, the rest-frame optical and near -infrared emissivities at various redshifts from surveys of galaxies, the m idinfrared and far-infrared emissivities of the local universe from the IRA S survey, the mean abundance of heavy elements at various epochs from surve ys of damped Ly alpha systems, and the global star formation rates at sever al redshifts from H alpha, mid-infrared, and submillimeter observations. Th e chemical enrichment history of the intergalactic medium implied by our mo dels is also consistent with the observed mean metal content of the Ly alph a forest at high redshifts. We infer that the dust associated with star-for ming regions is highly inhomogeneous and absorbs a significant fraction of the starlight, with only 41%-46% of the total in the extragalactic optical background and the remaining 59%-54% reprocessed by dust into the infrared background. The solutions presented here provide an intriguing picture of t he cosmic mean history of galaxies over much of the Hubble time. In particu lar, the process of galaxy formation appears to have undergone an early per iod of substantial inflow to assemble interstellar gas at z greater than or similar to 3, a subsequent period of intense star formation and chemical e nrichment at 1 less than or similar to z less than or similar to 3, and a r ecent period of decline in the gas content, star formation rate, optical st ellar emissivity, and infrared dust emissivity at z less than or similar to 1.