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The Lyman alpha emission line is an essential diagnostic tool for probing galaxy formation and evolution. Not only is it commonly the strongest observable line from high-redshift galaxies but from its shape detailed information about its host galaxy can be revealed. However, due to the scattering nature of Lya photons increasing their path length in a non-trivial way, if dust is present in the galaxy the line may be severely suppressed and its shape altered. In order to interpret observations correctly, it is thus of crucial significance to know how much of the emitted light actually escapes the galaxy. In the present work, using a combination of high-resolution cosmological hydro-simulations and an adaptively refinable Monte Carlo Lya radiative transfer code including an advanced model of dust, the escape fractions fₑsc of Lya radiation from high-redshift (z = 3. 6) galaxies are calculated. In addition to the average escape fraction, the variation of fₑsc in different directions and from different parts of the galaxies is investigated, as well as the effect on the emergent spectrum. Escape fractions from a sample of simulated galaxies of representative physical properties are found to decrease for increasing galaxy virial mass Mᵥir, from fₑsc approaching unity for Mᵥir ~ 10⁹ Mₛun to fₑsc less than 10% for Mᵥir ~ 10¹2 Mₛun. In spite of the dust being almost grey, it is found that the emergent spectrum is affected non-uniformly, with the escape fraction of photons close to the line center being much higher than of those in the wings, thus effectively narrowing the Lya line.
Laursen et al. (Tue,) studied this question.