Cosmic Emissivity and Background Intensity from Damped Lyman-Alpha Galaxies

We present a new method to compute the cosmic emissivity $\E_\nu$ and background intensity $J_\nu$. Our method is based entirely on data from quasar absorption-line studies, namely, the comoving density of HI 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 $\E_\nu$ and $J_\nu$ 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 $z\approx1$ 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.