Fragmentation and Evolution of Molecular Clouds. III: The Effect of Dust
  and Gas Energetics
  Dust and gas energetics are incorporated into a cluster-scale simulation of
star formation in order to study the effect of heating and cooling on the star
formation process. We build on our previous work by calculating separately the
dust and gas temperatures. The dust temperature is set by radiative equilibrium
between heating by embedded stars and radiation from dust. The gas temperature
is determined using an energy-rate balance algorithm which includes molecular
cooling, dust-gas collisional energy transfer, and cosmic-ray ionization. The
fragmentation proceeds roughly similarly to simulations in which the gas
temperature is set to the dust temperature, but there are differences. The
structure of regions around sink particles have properties similar to those of
Class 0 objects, but the infall speeds and mass accretion rates were, on
average, higher than those seen for regions forming only low-mass stars. The
gas and dust temperature have complex distributions not well modeled by
approximations that ignore the detailed thermal physics. There is no simple
relationship between density and kinetic temperature. In particular, high
density regions have a large range of temperatures, determined by their
location relative to heating sources. The total luminosity underestimates the
star formation rate at these early stages, before ionizing sources are
included, by an order of magnitude. As predicted in our previous work, a larger
number of intermediate mass objects form when improved thermal physics is
included, but the resulting IMF still has too few low mass stars. However, if
we consider recent evidence on core-to-star efficiencies, the match to the IMF
is improved.
