CO outflows from high-mass Class 0 protostars in Cygnus-X

TL;DR

This study investigates high-mass star formation in Cygnus-X by analyzing CO outflows from high-mass cores, revealing similarities to low-mass star formation processes and proposing a universal collapse timescale.

Contribution

It provides observational evidence that high-mass cores exhibit outflows similar to low-mass protostars and suggests a universal collapse timescale across different stellar masses.

Findings

Most high-mass cores drive clear outflows.

Outflow momentum flux scales linearly with envelope mass.

Collapse timescales are similar for all stellar masses.

Abstract

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.