M. A. Latif, D. R. G. Schleicher, M. Spaans
Numerical simulations suggest that the first galaxies are formed in
protogalactic halos with virial temperatures $\rm \geq 10^{4}$ K. The presence
of dust can significantly change the chemistry and dynamics of early galaxies.
We have performed high resolution cosmological simulations using the adaptive
mesh refinement code FLASH to study the influence of dust on the thermal
evolution of protogalactic halos and the assembly of the first galaxies in the
presence of a background UV flux. 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 (both in
the gas phase and on dust grains), 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 is
significantly enhanced in the presence of dust grains as compared to only gas
phase reactions, depending on the metal content. The presence of a background
UV flux strongly influences the formation of molecules by photodissociating
them. We also explore the evolution after a major merger, leading to the
formation of a binary disk. These disks have gas masses of 10^{7} M_{\odot} at
a redshift of 5.4. They are formed despite the strength of the background UV
flux and the metal content in our simulations. 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. We find
that 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. We also find that dust masses of a few times 10^{8}
M_{\odot} are required to observe the dust continuum emission from z 5
galaxies.
View original:
http://arxiv.org/abs/1110.4256
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