Lyman alpha emission from the first galaxies: Signatures of accretion
  and infall in the presence of line trapping
  The formation of the first galaxies is accompanied by large accretion flows
and virialization shocks, during which the gas is shock-heated to temperatures
of $\sim10^4$ K, leading to potentially strong fluxes in the Lyman alpha line.
Indeed, a number of Lyman alpha blobs has been detected at high redshift. In
this letter, we explore the origin of such Lyman alpha emission using
cosmological hydrodynamical simulations that include a detailed model of atomic
hydrogen as a multi-level atom and the effects of line trapping with the
adaptive mesh refinement code FLASH. We see that baryons fall into the center
of a halo through cold streams of gas, giving rise to a Lyman alpha luminosity
of at least $\rm 10^{44} erg s^{-1}$ at $\rm z=4.7$, similar to observed Lyman
alpha blobs. We find that a Lyman alpha flux of $\rm 5.0\times 10^{-17} erg
cm^{-2} s^{-1}$ emerges from the envelope of the halo rather than its center,
where the photons are efficiently trapped. Such emission can be probed in
detail with the upcoming James Webb Space Telescope (JWST) and will constitute
an important probe of gas infall and accretion.
