Feedback from OB stars on their parent cloud: Gas exhaustion rather than
  gas ejection
  Feedback from high-mass stars shapes the ISM of galaxies and thereby impacts
gas that will form future generations of stars. However, due to our inability
to track the time evolution of individual molecular clouds, quantifying the
exact role of feedback on their star formation history is an observationally
challenging task. In the present study, we take advantage of the unique
properties of the G316.75-00.00 high-mass star-forming ridge to determine how
feedback from O-stars impacts the dynamical stability of filaments. G316.75 is
a 13.6pc long ridge containing 18,900Msun of H2 gas which is half IR dark, half
IR bright. The IR bright half has already formed 4 O-type stars over the past
2Myr, while the IR dark half is still quiescent. Therefore, by assuming the gas
properties of the dark part represents an earlier evolutionary stage of the
bright part, we can quantify how feedback impacts these properties by
contrasting them. We use archive Herschel and molecular line data, tracing both
dense (NH3 and N2H+) and more diffuse (13CO) gas, to measure the ratio of
kinetic to gravitational energy per-unit-length, virial-ratio-per-line, across
the ridge for a range of gas volume densities. We show that despite the
presence of 4 embedded O-stars, feedback cannot unbind the ridge's mass except
for some small gas pockets near the O-stars. In fact, the virial-ratio-per-line
is almost indistinguishable for both parts of the ridge. These results are at
odds with most simulations where O-star-forming clouds are dispersed by
feedback within a few cloud free-fall time. We conclude that the discrepancy
between such simulations and our observations originates from different cloud
morphologies and average densities when the first O-star forms. These results
have important implications regarding, for instance, how feedback is
implemented within cosmological and galactic-scale simulations.
