Misc,
The Launching of Cold Clouds by Galaxy Outflows II: The Role of Thermal Conduction
(Feb 4, 2016)
Abstract
We explore the impact of electron thermal conduction on the evolution of
radiatively-cooled cold clouds embedded in flows of hot and fast material, as
occur in outflowing galaxies. Performing a parameter study of three-dimensional
adaptive mesh refinement hydrodynamical simulations, we show that electron
thermal conduction causes cold clouds to evaporate, but it can also extend
their lifetimes by compressing them into dense filaments. We distinguish
between low column-density clouds, which are disrupted on very short times, and
high-column density clouds with much-longer disruption times that are set by a
balance between impinging thermal energy and evaporation. We provide fits to
the cloud lifetimes and velocities that can be used in galaxy-scale simulations
of outflows, in which the evolution of individual clouds cannot be modeled with
the required resolution. Moreover, we show that the clouds are only accelerated
to a small fraction of the ambient velocity because compression by evaporation
causes the clouds to present a small cross-section to the ambient flow. This
means that either magnetic fields must suppress thermal conduction, or that the
cold clouds observed in galaxy outflows are not formed of cold material carried
out from the galaxy.
