CO outflows from high-mass Class 0 protostars in Cygnus-X
  As natural consequences of the accretion process, outflows are one of the few
(indirect) tracers of accretion. We used CO(2-1) PdBI observations towards 6
MDCs in Cygnus-X, containing 9 high-mass cores, to investigate what the
accretion process and origin of the material feeding the precursors of
high-mass stars are. We compared our sample to low-mass objects from the
literature and developed simple evolutionary models to reproduce the
observables. We find that 8/9 high-mass cores drive clear individual outflows
as true equivalents of Class 0 protostars in the high-mass regime. The
remaining core has only a tentative outflow detection. It could be amongst the
first examples of a true individual high-mass prestellar core. We find that the
momentum flux of high-mass objects has a linear relation to the envelope mass,
as a scale-up of the relations found for low-mass protostars. This suggests a
fundamental proportionality between accretion rates and mass reservoir,
suggesting identical collapse timescales for all masses. We conclude that if
the pre-collapse evolution is quasi-static, the fragmentation scale (which is
similar for all masses) would limit the size of the initial mass reservoirs,
leading to shorter free-fall times for higher mass stars. However, as we find
identical collapse timescales for all masses, a significant turbulent/magnetic
support is needed to slow down the collapse of the more massive envelopes in a
quasi-static view. With this support still to be discovered, and with
indications of large dynamics in pre-collapse gas for high-mass star formation,
we propose that such an identical collapse timescale implies that the initial
densities, which should set the duration of the collapse, should be similar for
all masses. This suggests that the mass that incorporates massive stars has to
have been accreted in a dynamical way from larger scales than those of low-mass
stars.
