Lyα Line Formation in Starbursting Galaxies. II. Extremely Thick, Dustless, and Static HiMedia

Abstract

We investigate the Lyα line transfer in nearby and high-redshift starbursting galaxies, where the effects of high optical depths and the role of dust in the scattering medium are expected to be conspicuous and should be treated in a very careful manner. We present our first results in a dustless, static, and uniform H I media with moderate Lyα line center optical depths τ0 = 103-106. We assume the temperatures of the media to be T = 101-104 K, and use a Monte Carlo technique. We investigate the basic processes of the line transfer and confirm the criterion of aτ0 > 103 for the validity of the diffusion approximation suggested by Neufeld in 1990, where a is the Voigt parameter. Adopting the model for evolution of a galactic supershell suggested by Tenorio-Tagle et al. in 1999, we performed calculations on the Lyα line formation for each evolutionary stage of an expanding supershell. The emergent Lyα profiles are characterized by the double peaks and the absorption trough at the line center. We found that the absorption troughs expected in most of the evolutionary stages are not wide enough to be observed with current instruments. However, the absorption trough in the Lyα emission profile from an expanding recombining supershell can be marginally detected.