CN Zeeman observations of the NGC 2264-C protocluster^⋆,⋆⋆

¹ ESO, Karl Schwarzschild Strasse 2, 85748 Garching bei München, Germany
e-mail: amaury@eso.org
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ IRAM, 300 rue de la Piscine, 38406 St Martin d’Hères, France

Received: 1 March 2012
Accepted: 2 June 2012

Abstract

From an observational point of view, the role of magnetic fields in star formation remains unclear, and two main theoretical scenarios have been proposed so far to regulate the star-formation processes. The first model assumes that turbulence in star-forming clumps plays a crucial role, and especially that protostellar outflow-driven turbulence is crucial to support cluster-forming clumps; while the second scenario is based on the consideration of a magnetically-supported clump. Previous studies of the NGC 2264-C protocluster indicate that, in addition to thermal pressure, some extra support might effectively act against the gravitational collapse of this cluster-forming clump. We previously showed that this extra support is not due to the numerous protostellar outflows, nor the enhanced turbulence in this protocluster. Here we present the results of the first polarimetric campaign dedicated to quantifying the magnetic support at work in the NGC 2264-C clump. Our Zeeman observations of the CN(1–0) hyperfine lines provide an upper limit to the magnetic field strength B_los ≲ 0.6 mG in the protocluster (projected along the line of sight). While these results do not provide sufficiently tight constraints to fully quantify the magnetic support at work in NGC 2264-C, they suggest that, within the uncertainties, the core could be either magnetically super or sub-critical, with the former being more likely.