From dusty filaments to massive stars: The case of NGC 7538 S
  We report on high-sensitivity and high-angular resolution archival
Submillimeter Array (SMA) observations of the large ($\sim$15000 AU) putative
circumstellar disk associated with the O-type protostar NGC 7538 S.
Observations of the continuum resolve this putative circumstellar disk into
five compact sources, with sizes $\sim$ 3000 AU and masses $\sim10 M_\odot$.
This confirm the results of recent millimeter observations made with CARMA/BIMA
towards this object. However, we find that from most of these compact sources
eject collimated bipolar outflows, revealed by our silicon monoxide (SiO {\it
J}=5-4) observations and confirm that these sources have a (proto)stellar
nature. All outflows are perpendicular to the large and rotating dusty
structure. We propose therefore that, rather than being a single massive
circumstellar disk, NGC 7538 S could be instead a large and massive contracting
or rotating filament that is fragmenting at scales of 0.1 to 0.01 pc to form
several B-type stars, via the standard process involving outflows and disks. As
in recent high spatial resolution studies of dusty filaments, our observations
also suggest that thermal pressure does not seem to be sufficient to support
the filament, so that either additional support needs to be invoked, or else
the filament must be in the process of collapsing. An SPH numerical simulation
of the formation of a molecular cloud by converging warm neutral medium flows
produces contracting filaments whose dimensions and spacings between the stars
forming within them, as well as their column densities, strongly resemble those
observed in the filament reported here.
