Using CLARA ( Code for Lyman Alpha Radiation Analysis ) we constrain the escape fraction of Lyman- \alpha radiation in galaxies in the redshift range 5 \lesssim z \lesssim 7 , based on the MareNostrum High-z Universe , a SPH cosmological simulation with more than 2 billion particles .
We approximate Lyman- \alpha Emitters ( LAEs ) as dusty gaseous slabs with Lyman- \alpha radiation sources homogeneously mixed in the gas .
Escape fractions for such a configuration and for different gas and dust contents are calculated using our newly developed radiative transfer code CLARA .
The results are applied to the MareNostrum High-z Universe numerical galaxies .
The model shows a weak redshift evolution and good agreement with estimations of the escape fraction as a function of reddening from observations at z \sim 2.2 and z \sim 3 .
We extend the slab model by including additional dust in a clumpy component in order to reproduce the UV continuum luminosity function and UV colours at redshifts z \gtrsim 5 .
The LAE Luminosity Function ( LF ) based on the extended clumpy model reproduces broadly the bright end of the LF derived from observations at z \sim 5 and z \sim 6 .
At z \sim 7 our model over-predicts the LF by roughly a factor of four , presumably because the effects of the neutral intergalactic medium are not taken into account .
The remaining tension between the observed and simulated faint end of the LF , both in the UV-continuum and Lyman- \alpha at redshifts z \sim 5 and z \sim 6 points towards an overabundance of simulated LAEs hosted in haloes of masses 1.0 \times 10 ^ { 10 } { { h ^ { -1 } { { M _ { \odot } } } } } \leq M _ { h } \leq 4.0 \times 10 ^ { 10 } { { h% ^ { -1 } { { M _ { \odot } } } } } .
Given the difficulties in explaining the observed overabundance by dust absorption , a probable origin of the mismatch are the high star formation rates in the simulated haloes around the quoted mass range .
A more efficient supernova feedback should be able to regulate the star formation process in the shallow potential wells of these haloes .