3D Lyα radiation transfer

II. Fitting the Lyman break galaxy MS 1512–cB58 and implications for Lyα emission in high-z starbursts

¹ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: daniel.schaerer@obs.unige.ch
² Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 avenue E. Belin, 31400 Toulouse, France

Received: 24 October 2007
Accepted: 7 January 2008

Abstract

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, A&A, 460, 397), 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 analyses 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 H i column density N_H. 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 N_H 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 of our scenario on the duty-cycle of Lyα emitters are also discussed.