Large-scale magnetic fields in Bok globules^⋆

¹ University of Kiel, Institute of Theoretical Physics and Astrophysics, Leibnizstr. 15, 24118 Kiel, Germany
e-mail: gbertrang@astrophysik.uni-kiel.de
² Assam University, Department of Physics, 788 011 Silchar, India

Received: 20 November 2013
Accepted: 27 March 2014

Abstract

Context. The role of magnetic fields in the star formation process is a contentious matter of debate. In particular, no clear observational proof exists of a general influence by magnetic fields during the initial collapse of molecular clouds.

Aims. Our aim is to examine magnetic fields and their influence on a wide range of spatial scales in low-mass star-forming regions.

Methods. We trace the large-scale magnetic field structure on scales of 10³−10⁵ AU in the local environment of Bok globules through optical and near-infrared polarimetry and combine these measurements with existing submillimeter measurements, thereby characterizing the small-scale magnetic field structure on scales of 10²−10³ AU.

Results. For the first time, we present polarimetric observations in the optical and near-infrared of the three Bok globules B335, CB68, and CB54, combined with archival observations in the submillimeter and the optical. We find a significant polarization signal (P ≳ 2%,P/σ_P > 3) in the optical and near-infrared for all three globules. Additionally, we detect a connection between the structure on scales of 10²−10³ AU to 10³−10⁴ AU for both B335 and CB68. Furthermore, for CB54, we trace ordered polarization vectors on scales of ~10⁵ AU. We determine a magnetic field orientation that is aligned with the CO outflow in the case of CB54, but nearly perpendicular to the CO outflow for CB68. For B335 we find a change in the magnetic field oriented toward the outflow direction, from the inner core to the outer regions.

Conclusions. We find strongly aligned polarization vectors that indicate dominant magnetic fields on a wide range of spatial scales.