Large-scale magnetic fields in Bok globules

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. Method: We trace the large-scale magnetic field structure on scales of 10^3-10^5 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 10^2-10^3 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/sigma(P)>3) in the optical and near-infrared for all three globules. Additionally, we detect a connection between the structure on scales of 10^2-10^3 AU to 10^3-10^4 AU for both B335 and CB68. Furthermore, for CB54, we trace ordered polarization vectors on scales of ~10^5 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. Conclusion: We find strongly aligned polarization vectors that indicate dominant magnetic fields on a wide range of spatial scales.