Shock-multicloud interactions in galactic outflows -- II. Radiative
  fractal clouds and cold gas thermodynamics
  Galactic winds are crucial to the cosmic cycle of matter, transporting
material out of the dense regions of galaxies. Observations show the
coexistence of different temperature phases in such winds, which is not easy to
explain. We present a set of 3D shock-multicloud simulations that account for
radiative heating and cooling at temperatures between $10^2\,\rm K$ and
$10^7\,\rm K$. The interplay between shock heating, dynamical instabilities,
turbulence, and radiative heating and cooling creates a complex multi-phase
flow with a rain-like morphology. Cloud gas fragments and is continuously
eroded, becoming efficiently mixed and mass loaded. The resulting warm mixed
gas then cools down and precipitates into new dense cloudlets, which repeat the
process. Thus, radiative cooling is able to sustain fast-moving dense gas by
aiding condensation of gas from warm clouds and the hot wind. In the ensuing
outflow, hot gas with temperatures $\gtrsim 10^6\,\rm K$ outruns the warm and
cold phases, which reach thermal equilibrium near $\approx 10^4\,\rm K$ and
$\approx 10^2\,\rm K$, respectively. Although the volume filling factor of hot
gas is higher in the outflow, most of the mass is concentrated in dense gas
cloudlets and filaments with these temperatures. More porous multicloud layers
result in more vertically extended outflows, and dense gas is more efficiently
produced in more compact layers. The cold phase is not accelerated by
ram-pressure, but, instead, precipitates from warm and mixed gas out of thermal
equilibrium. This cycle can explain the presence of high-velocity H\,{\sc i}
gas with $N_{\rm H\,{\scriptstyle I}}=10^{19-21}\,\rm cm^{-2}$ and $\Delta
v_{{\rm FWHM}}\lesssim37\,\rm km\,s^{-1}$ in the Galactic centre outflow.
