Formation of prestellar cores via non-isothermal gas fragmentation
  Sheet-like clouds are common in turbulent gas and perhaps form via collisions
between turbulent gas flows. Having examined the evolution of an isothermal
shocked slab in an earlier contribution, in this work we follow the evolution
of a sheet-like cloud confined by (thermal)pressure and gas in it is allowed to
cool. The extant purpose of this endeavour is to study the early phases of
core-formation. The observed evolution of this cloud supports the conjecture
that molecular clouds themselves are three-phase media (comprising viz. a
stable cold and warm medium, and a third thermally unstable medium), though it
appears, clouds may evolve in this manner irrespective of whether they are
gravitationally bound. We report, this sheet fragments initially due to the
growth of the thermal instability and some fragments are elongated,
filament-like. Subsequently, relatively large fragments become gravitationally
unstable and sub-fragment into smaller cores. The formation of cores appears to
be a three stage process : first, growth of the thermal instability leads to
rapid fragmentation of the slab; second, relatively small fragments acquire
mass via gas-accretion and/or merger and third, sufficiently massive fragments
become susceptible to the gravitational instability and sub-fragment to form
smaller cores. We investigate typical properties of clumps (and smaller cores)
resulting from this fragmentation process. Findings of this work support the
suggestion that the weak velocity field usually observed in dense clumps and
smaller cores is likely seeded by the growth of dynamic instabilities.
Simulations were performed using the smooth particle hydrodynamics algorithm.
