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Though Lyman alpha emission (Lya) is one of the most used tracers of massivestar formation at high redshift, a correct understanding of radiation transfereffects by neutral gas is required to properly quantify the star formation ratealong the history of the Universe. We are embarked in a program to study theproperties of the Lya emission (spectral profile, spatial distribution,relation to Balmer lines intensity,...) in several local starburst galaxies. Wepresent here the results obtained for IRAS 08339+6517.  Using evolutionary population synthesis models, we have characterized theproperties of the starburst (UV continuum, Halpha, total infrared and X-rayemissions, etc.), which transformed 1.4e+8 Mo of gas into stars around 5-6 Myrago. In addition to the central compact emission blob, we have identified adiffuse Lya emission component smoothly distributed over the whole central areaof IRAS 08339+6517. This diffuse emission is spatially decoupled from the UVcontinuum, the Halpha emission or the Halpha/Hbeta ratio. Both locally andglobally, the Lya/Halpha ratio is lower than the Case B predictions, even afterreddening correction, with an overall Lya escape fraction of only 4%.  We conclude that in IRAS 08339+6517 the resonant scattering of Lya photons byan outflowing shell of neutral gas causes their highly-efficient destruction bydust, which explains the low Lya escape fraction measured. These results stressagain the importance of a proper correction of scattering and transfer effectswhen using Lya to derive the star formation rate in high-redshift galaxies.

Physical properties and evolutionary state of the Lyman alpha emitting starburst galaxy IRAS 08339+6517