Stellar feedback as the origin of an extended molecular outflow in a
  starburst galaxy
  Recent observations have revealed that starburst galaxies can drive molecular
gas outflows through stellar radiation pressure. Molecular gas is the phase of
the interstellar medium from which stars form, so these outflows curtail
stellar mass growth in galaxies. Previously known outflows, however, involve
small fractions of the total molecular gas content and are restricted to
sub-kiloparsec scales. It is also apparent that input from active galactic
nuclei is in at least some cases dynamically important, so pure stellar
feedback has been considered incapable of aggressively terminating star
formation on galactic scales. Extraplanar molecular gas has been detected in
the archetype starburst galaxy M82, but so far there has been no evidence that
starbursts can propel significant quantities of cold molecular gas to the same
galactocentric radius (~10 kpc) as the warmer gas traced by metal absorbers.
Here we report observations of molecular gas in a compact (effective radius 100
pc) massive starburst galaxy at z=0.7, which is known to drive a fast outflow
of ionized gas. We find that 35 per cent of the total molecular gas is
spatially extended on a scale of approximately 10 kpc, and one third of this
has a velocity of up to 1000 km/s. The kinetic energy associated with this
high-velocity component is consistent with the momentum flux available from
stellar radiation pressure. This result demonstrates that nuclear bursts of
star formation are capable of ejecting large amounts of cold gas from the
central regions of galaxies, thereby strongly affecting their evolution.
