We extend a previous study of Lyman Alpha Emitters ( LAEs ) based on hydrodynamical cosmological simulations , by including two physical processes important for LAEs : ( a ) Ly \alpha and continuum luminosities produced by cooling of collisionally excited H \scriptstyle I in the galaxy , ( b ) dust formation and evolution ; we follow these processes on a galaxy-by-galaxy basis .
H \scriptstyle I cooling on average contributes 16-18 % of the Ly \alpha radiation produced by stars , but this value can be much higher in low mass LAEs and further increased if the H \scriptstyle I is clumpy .
The continuum luminosity is instead almost completely dominated by stellar sources .
The dust content of galaxies scales with their stellar mass , M _ { dust } \propto M _ { * } ^ { 0.7 } and stellar metallicity , Z _ { * } , such that M _ { dust } \propto Z _ { * } ^ { 1.7 } .
As a result , the massive galaxies have Ly \alpha escape fraction as low as f _ { \alpha } = 0.1 , with a LAE-averaged value decreasing with redshift : \langle f _ { \alpha } \rangle = ( 0.33 , 0.23 ) at z = ( 5.7 , 6.6 ) .
The UV continuum escape fraction shows the opposite trend with z , possibly resulting from clumpiness evolution .
The model successfully reproduces the observed Ly \alpha and UV luminosity functions at different redshifts and the Ly \alpha equivalent width scatter to a large degree , although the observed distribution appears to be more more extended than the predicted one .
We discuss possible reasons for such tension .