  Numerical simulations suggest that the first galaxies are formed in
protogalactic halos with virial temperatures >= 10^4 K. It is likely that such
halos are polluted with trace amounts of metals produced by the first
generation of stars. The presence of dust can significantly change the
chemistry and dynamics of early galaxies. In this article, we aim to assess the
role of dust on the thermal and dynamical evolution of the first galaxies in
the presence of a background UV flux, and its implications for the
observability of Lyman alpha emitters and sub-mm sources. We have performed
high resolution cosmological simulations using the adaptive mesh refinement
code FLASH to accomplish this goal. We have developed a chemical network
appropriate for these conditions and coupled it with the FLASH code. The main
ingredients of our chemical model include the formation of molecules, a
multi-level treatment of atomic hydrogen, line trapping of Lyman alpha photons
and, photoionization and photodissociation processes in a UV background. We
found that the formation of molecules (H_{2} and HD) is significantly enhanced
in the presence of dust grains. The presence of a background UV flux strongly
influences the formation of molecules by photodissociating them. We explore the
evolution after a major merger, leading to the formation of a binary disk.
These disks have gas masses of ~10^{7} M_sun at a redshift of 5.4. Each disk
lies in a separate subhalo as a result of the merger event. The disks are
supported by turbulent pressure due to the highly supersonic turbulence present
in the halo. The presence of dust does not significantly reduce the Lyman alpha
emission. The emission of Lyman alpha is extended and originates from the
envelope of the halo due to line trapping effects. We also find that dust
masses of 10^8 M_sun are required to observe the dust continuum emission from z
5 galaxies with ALMA.
