Dynamical Properties of Molecular-forming Gas Clumps in Galaxies at the
  Epoch of Reionization
  We study the properties of molecular-forming gas clumps (MGCs) at the epoch
of reionization using cosmological zoom-in simulations. We identify MGCs in a
z=6 prototypical galaxy ("Althaea") using an H2 density-based clump finder. We
compare their mass, size, velocity dispersion, gas surface density, and virial
parameter (alpha_vir) to observations. In Althaea, the typical MGC mass and
size are Mgas=10^6.5 Msun and R=45-100 pc, which are comparable to those found
in nearby spirals and starburst galaxies. MGCs are highly supersonic and
supported by turbulence, with rms velocity dispersions of sigma_gas=20-100 km
s^-1 and pressure of P/k_B=10^7.6 K cm^-3 (i.e., >1000x with respect to the
Milky Way), similar to those found in nearby and z~2 gas-rich starburst
galaxies. In addition, we perform stability analysis to understand the origin
and dynamical properties of MGCs. We find that MGCs are globally stable in the
main disk of Althaea. Densest regions where star formation is expected to take
place in clouds and cores on even smaller scales instead have lower alpha_vir
and Toomre-Q values. Detailed studies of the star-forming gas dynamics at the
epoch of reionization thus require a spatial resolution of <40 pc (=0.01"),
which is within reach with the Atacama Large (sub-)Millimeter Array and the
Next Generation Very Large Array.
