  We present the first Lyman Alpha Emitter (LAE) study that combines: (i)
cosmological SPH simulations run using GADGET-2, (ii) radiative transfer
simulations (CRASH), and (iii) a previously developed LAE model. This complete
LAE model accounts for the intrinsic LAE Lyman Alpha/continuum luminosity, dust
enrichment and Lyman Alpha transmission through the intergalactic medium (IGM),
to quantify the effects of reionization, dust and velocity fields on the Lyman
Alpha and UV Luminosity Functions (LF). We find that a model neglecting dust
sorely fails to reproduce either the slope or the magnitude of the observed
Lyman Alpha and UV LFs. Clumped dust is required to simultaneously fit the
observed UV and Lyman Alpha LFs, such that the intrinsic Lyman
Alpha-to-continuum luminosity is enhanced by a factor f_alpha/f_c ~ 1.5 (3.7)
excluding (including) peculiar velocities. The higher value including velocity
fields arises since LAEs reside in large potential wells and inflows decrease
their Lyman Alpha transmission. For the first time, a degeneracy is found
between the the ionization state of the IGM and the clumping of dust inside
high-redshift galaxies. The Lyman Alpha LF at z ~ 5.7 can be well reproduced
(to within a 5 sigma error) by a wide range of IGM average neutral hydrogen
fraction, 3.4/10^3 to 0.16, provided that the increase in the Lyman Alpha
transmission through a more ionized IGM is compensated by a decrease in the
Lyman Alpha escape fraction from the galaxy due to dust absorption. The
physical properties of LAEs are presented, along with a discussion of the
assumptions adopted.
