The effect of dust geometry on the Lyman-alpha output of galaxies
  We present the optical spectroscopic follow-up of 31 z=0.3 Lyman-alpha (Lya)
emitters, previously identified by Deharveng et al. (2008). We find that 17% of
the Lya emitters have line ratios that require the hard ionizing continuum
produced by an AGN. The uniform dust screen geometry traditionally used in
studies similar to ours is not able to simultaneously reproduce the observed
high Lya/Halpha and Halpha/Hbeta line ratios. We consider different
possibilities for the geometry of the dust around the emitting sources. We find
that also a uniform mixture of sources and dust does not reproduce the observed
line ratios. Instead, these are well reproduced by a clumpy dust screen. This
more realistic treatment of the geometry results in extinction corrected
(Lya/Halpha)_C values consistent with Case B recombination theory, whereas a
uniform dust screen model would imply values (Lya/Halpha)_C higher than 8.7.
Our analysis shows that there is no need to invoke "ad-hoc" multi phase media
in which the Lya photons only scatter between the dusty clouds and eventually
escape.
