Outflows and extended [CII] halos in high redshift galaxies
  Recent stacked ALMA observations have revealed that normal, star-forming
galaxies at $z\approx 6$ are surrounded by extended ($\approx
10\,\mathrm{kpc}$) [CII] emitting halos which are not predicted by the most
advanced, zoom-in simulations. We present a model in which these halos are the
result of supernova-driven cooling outflows. Our model contains two free
parameters, the outflow mass loading factor, $\eta$, and the parent galaxy dark
matter halo circular velocity, $v_c$. The outflow model successfully matches
the observed [CII] surface brightness profile if $\eta = 3.20 \pm 0.10$ and
$v_c = 170 \pm 10{\,\rm km\,s^{-1}}$, corresponding to a dynamical mass of
$\approx 10^{11}\, \mathrm{M}_\odot$. The predicted outflow rate and velocity
range are $128 \pm 5 \,\mathrm{M}_\odot {\rm yr}^{-1}$ and $300-500 {\,\rm
km\,s^{-1}}$, respectively. We conclude that: (a) extended halos can be
produced by cooling outflows; (b) the large $\eta$ value is marginally
consistent with starburst-driven outflows, but it might indicate additional
energy input from AGN; (c) the presence of [CII] halos requires an ionizing
photon escape fraction from galaxies $f_{\rm esc} \ll 1$. The model can be
readily applied also to individual high-$z$ galaxies, as those observed, e.g.,
by the ALMA ALPINE survey now becoming available.
