The physical and dynamical structure of Serpens: Two very different
  sub-(proto)clusters
  The Serpens North Cluster is a nearby low mass star forming region which is
part of the Gould Belt. It contains a range of young stars thought to
correspond to two different bursts of star formation and provides the
opportunity to study different stages of cluster formation. This work aims to
study the molecular gas in the Serpens North Cluster to probe the origin of the
most recent burst of star formation in Serpens. Transitions of the C17O and
C18O observed with the IRAM 30m telescope and JCMT are used to study the mass
and velocity structure of the region while the physical properties of the gas
are derived using LTE and non-LTE analyses of the three lowest transitions of
C18O. The molecular emission traces the two centres of star formation which are
seen in submillimetre dust continuum emission. In the ~40M_sun NW sub-cluster
the gas and dust emission trace the same structures although there is evidence
of some depletion of the gas phase C18O. The gas has a very uniform temperature
(~10K) and velocity (~8.5km/s) throughout the region. This is in marked
contrast to the SE sub-cluster. In this region the dust and the gas trace
different features, with the temperature peaking between the submillimetre
continuum sources, reaching up to ~14K. The gas in this region has double
peaked line profiles which reveal the presence of a second cloud in the line of
sight. The submillimetre dust continuum sources predominantly appear located in
the interface region between the two clouds. Even though they are at a similar
stage of evolution, the two Serpens sub-clusters have very different
characteristics. We propose that these differences are linked to the initial
trigger of the collapse in the regions and suggest that a cloud-cloud collision
could explain the observed properties.
