Fluorescent Lyα emission from the high-redshift intergalactic medium

We combine a high-resolution hydro simulation of the Lambda CDM cosmology with two radiative transfer schemes ( for continuum and line radiation) to predict the properties, spectra, and spatial distribution of fluorescent Ly alpha emission at z similar to 3. We focus on line radiation produced by recombinations in the dense intergalactic medium ionized by UV photons. In particular, we consider both a uniform background and the case in which gas clouds are illuminated by a nearby quasar. We find that the emission from optically thick regions is substantially less than predicted from the widely used static, plane-parallel model. The effects induced by a realistic velocity field and by the complex geometric structure of the emitting regions are discussed in detail. We make predictions for the expected brightness and size distributions of the fluorescent sources. Our results account for recent null detections and can be used to plan new observational campaigns both in the field ( to measure the intensity of the diffuse UV background) and in the proximity of bright quasars ( to understand the origin of high column density absorbers).