1512–cB58 and implications for Lyα emission in high-z starbursts

Aims. To understand the origin of the Lyα line profile of the prototypical Lyman break galaxy (LBG) MS 1512–cB58 and other similar objects. To attempt a consistent fit of Lyα and other UV properties of this galaxy. To understand the main physical parameter(s) responsible for the large variation of Lyα line strengths and profiles observed in LBGs. Methods. Using our 3D Lyα radiation transfer code (Verhamme et al. 2006), we compute the radiation transfer of Lyα and UV continuum photons including dust. Observational constraints on the neutral gas (column density, kinematics, etc.) are taken from other analysis of this object. Results. The observed Lyα profile of MS 1512–cB58 is reproduced for the first time taking radiation transfer and all observational constraints into account. The observed absorption profile is found to result naturally from the observed amount of dust and the relatively high HI column density NH. Radiation transfer effects and suppresion by dust transform a strong intrinsic Lyα emission with EW(Lyα) >∼ 60 Å into the observed faint superposed Lyα emission peak. We propose that the vast majority of LBGs have intrinsically EW(Lyα) ∼ 60–80 Å or larger, and that the main physical parameter responsible for the observed variety of Lyα strengths and profiles in LBGs is NH and the accompanying variation of the dust content. Observed EW(Lyα) distributions, Lyα luminosity functions, and related quantities must therefore be corrected for radiation transfer and dust effects. The implications from our scenario on the duty-cycle of Lyα emitters are also discussed.