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, including the integrated background light from galaxy counts, the optical and near-infrared emissivities from galaxy surveys, the local infrared emissivities from the IRAS survey, the mean abundance of heavy elements from surveys of damped Lyman-alpha systems, and the global star formation rates from H$\alpha$ surveys and submillimeter observations. The solutions presented here suggest that the process of galaxy formation appears to have undergone an early period of substantial inflow to assemble interstellar gas at $z\gtrsim3$, a subsequent period of intense star formation and chemical enrichment at $1\lesssim z\lesssim3$, and a recent period of rapid decline in the gas content, star formation rate, optical stellar emissivity, and infrared dust emission at $z\lesssim1$. [abridged version] 
Yichuan C. Pei, S. Michael Fall, and Michael G. Hauser (STScI)