Lyα resonant scattering in young galaxies:: Predictions from cosmological simulations

We present results obtained with a three-dimensional, Ly alpha radiative transfer code applied to a fully cosmological galaxy formation simulation. The developed Monte Carlo code is capable of treating an arbitrary distribution of source Ly alpha emission, neutral hydrogen density, temperature, and peculiar velocity of the interstellar medium. We investigate the influence of resonant scattering on the appearance and properties of young galaxies by applying the code to a simulated Lyman break galaxy at redshift z = 3.6, star formation rate 22 M. yr(-1), and total Ly alpha luminosity 20 x 10(-43) ergs s(-1). It is found that resonant scattering of Ly alpha radiation can explain that young galaxies are frequently observed to be more extended on the sky in Ly alpha than in the optical. Moreover, it is shown that, for the system investigated, due to the anisotropic escape of the photons, the observed maximum surface brightness can differ by more than an order of magnitude, and the total derived luminosity by a factor of similar to 4, depending on the orientation of the system relative to the observer.