Lyman alpha emission from thick clouds photoionized by the metagalactic radiation

Abstract

We present calculations of the expected Lyα surface brightness and emergent spectral line profiles from thick (N H ≥10 20 cm −2 ), massive (≥ 10 10 M ○ .) clouds at high redshift (z ≥ 3) photoionized by the metagalactic background radiation. Our results directly apply to the damped Lyα systems and to the «pancakes» that are expected to form at large redshift in the Sunyaev-Zel'dovich theory of cluster formation. We consider both quasar-dominated and stellar-dominated metagalactic fluxes. For the quasar-dominated metagalactic flux, we use two energy distributions: a power law with index − 1, which is representative of a «raw» (unfiltered) quasar energy distribution, and a distribution from Miralda-Escude and Ostriker [ApJ, 350, 1 (1990)] in which the ionizing background arises from quasar emission filtered by dust intervening galaxies and by Lyα forest clouds