ATTENUATION OF LYMAN-ALPHA EMISSION BY DUST IN DAMPED LYMAN-ALPHA SYSTEMS

We derive relations between the Ly-alpha surface brightness, star formation rate, and abundance of dust in damped Ly-alpha absorption systems. These are idealized as plane-parallel objects in which the sources of Ly-alpha photons are either distributed throughout the gas or confined to a thin, central sheet. For the dust-to-gas ratio in the damped Ly-alpha systems, we adopt the typical value inferred from the reddening of background quasars. We then use the results of several recent searches for Ly-alpha emission to set limits on, and in one case, estimate the star formation rate per unit area of the damped. Ly-alpha systems. When the H I column density exceeds 5 x 10(20) cm-2, the attenuation of Ly-alpha emission is large and the star formation rate can be one or two orders of magnitude higher than that in the solar neighborhood. The large uncertainties are caused by the unknown orientations of the damped Ly-alpha systems and the unknown distributions of stars, gas, and dust within them. However, when the H I column density is less than 5 x 10(20) cm-2, the attenuation is smaller and the limits on or value of the star formation rate per unit area are similar to that in the solar neighborhood, a few M. Gyr-1 pc-2.