Probing the role of the magnetic field in the formation of structure in molecular clouds with Planck
Abstract
The Planck observations of intensity and polarization of thermal emission from Galactic dust over the whole sky, and down to scales that probe the interiors of nearby molecular clouds, constitute an unprecedented data set for the study of the morphology of the magnetic field.Within ten nearby (d < 450 pc) Gould Belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The relative orientation is evaluated pixel by pixel and analyzed in bins of column density using the novel statistical tool called "Histogram of Relative Orientations".Within most clouds we find that the relative orientation changes progressively with increasing NH, from preferentially parallel or having no preferred orientation to preferentially perpendicular.In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck.We compare the deduced plane-of-the-sky magnetic field strength with estimates we obtain from the Davis-Chandrasekhar-Fermi method and with the line-of-sight magnetic field strengths derived from Zeeman splitting observations towards some of the studied regions.Finally, we discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.This work is presented on behalf of the Planck Collaboration.
- Publication:
-
IAU General Assembly
- Pub Date:
- August 2015
- Bibcode:
- 2015IAUGA..2252936D