Cosmic emissivity and background intensity from damped Lyman-alpha galaxies

We present a new method to compute the cosmic emissivity E(v) and background intensity J(v). Our method is based entirely on data from quasar absorption-line studies, namely, the comoving density of H I and the mean metallicity and dust-to-gas ratio in damped Ly alpha galaxies. These observations, when combined with models of cosmic chemical evolution, are sufficient to determine the comoving rate of star formation as a function of redshift. From this, we compute E(v), and J(v) using stellar population synthesis models. Our method includes a self-consistent treatment of the absorption and reradiation of starlight by dust. In all of our calculations, the near-UV emissivity declines rapidly between z approximate to 1 and z = 0, in agreement with estimates from the Canada-France Redshift Survey. The background intensity is consistent with a wide variety of observational limits and with a tentative detection at far-IR wavelengths.