Polarisation around filamentary dark cloud GF 9

When visible and NIR polarization data are combined, no evidence is found for a plateau in the polarization above extinction A_V_~1.3, as seen in dark clouds in Taurus. This lack of saturation effect suggests that even in the denser parts of GF 9 magnetic fields can be probed.

The visible polarization is smooth and has a well-defined orientation. In the core region, the IR and FIR data are also well defined, but each with a different direction. A multiscale analysis of the magnetic field shows that on the scale of a few times the mean radial dimension of the molecular cloud, it is as if the magnetic field were blind to the spatial distribution of the filaments, while on smaller scales in the core region, multiwavelength polarimetry shows a rotation of the magnetic field lines in these denser phases.