A Dynamically Collapsing Core and a Precursor of a Core in a Filament
  Supported by Turbulent and Magnetic Pressures
  To study physical properties of the natal filament gas around the cloud core
harboring an exceptionally young low-mass protostar GF9-2, we carried out J=1-0
line observations of 12CO, 13CO, and C18O molecules using the Nobeyama 45m
telescope. The mapping area covers ~1/5 of the whole filament. Our 13CO and
C18O maps clearly demonstrate that the core formed at the local density maxima
of the filament, and the internal motions of the filament gas are totally
governed by turbulence with Mach number of ~2. We estimated the scale height of
the filament to be H = 0.3 ~ 0.7 pc, yielding the central density of n_c = 700
~4200 cm^-3. Our analysis adopting an isothermal cylinder model shows that the
filament is supported by the turbulent and magnetic pressures against the
radial and axial collapse due to self-gravity. Since both the dissipation time
scales of the turbulence and the transverse magnetic fields can be comparable
to the free-fall time of the filament gas of 10^6 years, we conclude that the
local decay of the supersonic turbulence made the filament gas locally
unstable, hence making the core collapse. Furthermore, we newly detected a gas
condensation with velocity width enhancement to ~0.3 pc south-west of the GF9-2
core. The condensation has a radius of ~0.15 pc and an LTE mass of ~5 Msun. Its
internal motion is turbulent with Mach number of ~3, suggestive of a
gravitationally unbound state. Considering the uncertainties in our estimates,
however, we propose that the condensation is a precursor of a cloud core which
would have been produced by the collision of the two gas components identified
in the filament.
