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It has been suggested that radiative transfer effects may explain theunusually high equivalent widths (EWs) of the Lya line, observed occasionallyfrom starburst galaxies, especially at high redshifts. If the dust is locked upinside high-density clouds dispersed in an empty intercloud medium, the Lyaphotons could scatter off of the surfaces of the clouds, effectively havingtheir journey confined to the dustless medium. The continuum radiation, on theother hand, does not scatter, and would thus be subject to absorption insidethe clouds. This scenario is routinely invoked when Lya EWs higher than what isexpected theoretically are observed, although the ideal conditions under whichthe results are derived usually are not considered. Here we systematicallyexamine the relevant physical parameters in this idealized framework, testingwhether any astrophysically realistic scenarios may lead to such an effect. Itis found that although clumpiness indeed facilitates the escape of Lya, it ishighly unlikely that any real interstellar media should result in apreferential escape of Lya over continuum radiation. Other possible causes arediscussed, and it is concluded that the observed high EWs are more likely to becaused by cooling radiation from cold accretion and/or anisotropic escape ofthe Lya radiation.

On the (non-)enhancement of the Lyman \alpha\ equivalent width by a multiphase interstellar medium