P Cygni type Lyα from starburst galaxies

P Cygni type Lyalpha emission is exhibited in the spectra of nearly half the starburst galaxies in either the nearby Universe or the high-z Universe. Such emission is presumably formed by an expanding supershell surrounding star-forming regions. We assume that the Lyalpha photons from the central star-forming regions transfer in a spherical galactic supershell of uniform neutral hydrogen that is expanding radially in a bulk flow. We apply the Monte Carlo code developed previously for static and plane-parallel media. We consider typical cases in which the supershell has Lyalpha line-centre optical depth tau(0) = 10(5)-10(7), a radial expansion velocity V-exp approximate to 300 km s(-1) and turbulence b similar or equal to 40 km s(-1). We find that a series of emission peaks appear redward of the systemic redshift, their frequencies being given by (2N - 1)V-exp, where the number of back-scatterings N is greater than zero. We also investigate how the emergent profiles are changed in accordance with the expansion velocity and the column density of the supershell. We find that the number and the flux ratios of emission peaks are determined by interplay of the two parameters. It is very important that the kinematics of the supershell is imprinted on both the widths of the peaks and the velocity differences between peaks. We discuss the effects of dust extinction and the implication of our work in relation to recent spectroscopic observations of starburst galaxies.