Detection of a high-redshift molecular outflow in a primeval
  hyperstarburst galaxy
  We report the discovery of a high-redshift, massive molecular outflow in the
starburst galaxy SPT0346-52 ($z=5.656$) via the detected absorption of
high-excitation water transitions (H$_2$O $4_{2,3}-4_{1,4}$ and H$_2$O
$3_{3,0}-3_{2,1}$) with the Atacama Large Millimeter/submillimeter Array
(ALMA). The host galaxy is one of the most powerful starburst galaxies at high
redshift (star formation rate; SFR $\sim3,600$M$_\odot$year$^{-1}$), with an
extremely compact ($\sim320$pc) star formation region and a star formation rate
surface density ($\Sigma_{SFR}\sim5,500$M$_{\odot}~$year$^{-1}~$kpc$^{-2}$)
five times higher than `maximum' (i.e. Eddington-limited) starbursts, implying
a highly transient phase. The estimated outflow rate is
$\sim500$M$_{\odot}$year$^{-1}$, which is much lower than the SFR, implying
that in this extreme starburst the outflow capabilities saturate and the
outflow is no longer capable of regulating star formation, resulting in a
runaway process in which star formation will use up all available gas in less
than 30Myr. Finally, while previous kinematic investigations of this source
revealed possible evidence for an ongoing major merger, the coincidence of the
hyper-compact starburst and high-excitation water absorption indicates that
this is a single starburst galaxy surrounded by a disc.
