The physical and dynamical structure of Serpens^*,**

Two very different sub-(proto)clusters

¹ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK e-mail: Ana.Cabral@postgrad.manchester.ac.uk
² School of Physics, University of Exeter, Exeter EX4 4QL, UK
³ Department of Physics, Bucknell University, Lewisburg, PA 17837, USA
⁴ Astrophysics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE, UK
⁵ Kavli Institute for Cosmology, c/o Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK

Received: 19 December 2009
Accepted: 17 May 2010

Abstract

Context. 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.

Aims. 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.

Methods. Transitions of the C¹⁷O and C¹⁸O observed with the IRAM 30 m 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.

Results. The molecular emission traces the two centres of star formation which are seen in submillimetre dust continuum emission. In the ~40  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 (~10 K) and velocity (~8.5 km s^-1) 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 ~14 K. 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.

Conclusions. 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.