Constraints on star formation theories from the Serpens molecular cloud
L. Olmi & L. Testi
We have mapped the large-scale structure of the Serpens cloud core
using moderately optically thick (13CO(1--0) and
CS(2--1)) and optically thin tracers (C18O(1--0), C34S(2--1), and
N2H+(1--0)), using the 16-element focal plane array
operating at a wavelength of 3mm at the Five College Radio Astronomy
Our main goal was to study the large-scale distribution of the molecular
gas in the Serpens region and
to understand its relation with the denser
gas in the cloud cores, previously studied at high angular resolution.
All our molecular tracers show two main gas condensations, or sub-clumps,
roughly corresponding to the North-West and South-East clusters
of submillimeter continuum sources.
We also carried out a kinematical study of the Serpens cloud.
The 13CO and C18O(1--0) maps of the centroid velocity show an increasing,
smooth gradient in velocity from East to West, which we think
may be caused by a global rotation of the Serpens molecular cloud whose
rotation axis is roughly aligned in the SN direction.
Although it appears that
the cloud angular momentum is not sufficient for being dynamically important
in the global evolution of the cluster, the fact that the observed
molecular outflows are roughly aligned with it may suggest a link between
the large-scale angular momentum and the circumstellar disks around
individual protostars in the cluster.
We also used the normalized centroid velocity difference as an infall
indicator. We find two large regions of the map, approximately coincident
with the SE and NW sub-clumps, which are undergoing an infalling motion.
Although our evidence is not conclusive, our data appear to be in qualitative
agreement with the expectation of a slow contraction followed by a rapid
and highly efficient star formation phase in localized high density regions.