Recovering 3D Information on Interstellar Magnetic Fields using Multi-Wavelength Dust Polarized Emission

Lapo Fanciullo^1*

¹Department of Physics, NCHU, Taichung, Taiwan

* Presenter:Lapo Fanciullo, email:lfanciullo.astro@gmail.com

The polarization of far-infrared (FIR) dust emission is one of the most important tracers of interstellar magnetic fields, and is often to estimate magnetic field disorder and grain alignment efficiency. Polarimetry is therefore central to many astrophysical fields, including star formation and galaxy evolution on cosmic times.
However, polarization from dust emission can only show the projection of the magnetic field on the plane of the sky. This is the main limitation of dust polarization as a tracer. This issue can be alleviated by using multi-band FIR polarimetry, as opposed to single-band. In environment with strong temperature gradients on the line of sight – such as molecular clouds – different bands are sensitive to dust at different temperature, which will be generally be located at different depths. A change in polarization angle with wavelength can in principle be used to reconstruct the change in magnetic field orientation along the line of sight.
I will present our team’s results for a pilot study of multi-wavelength polarization in the star-forming region NGC 2071, as well as our work in progress in rho Ophiuchi. The analysis combines long-wavelength (850 μm) data from POL-2 at JCMT, observed as part of the BISTRO survey, with short-wavelength (~100-200 μm) data from HAWC+ on SOFIA. We detect a wavelength dependence of the polarization angles which is most likely caused by a rotation of the magnetic field lines within the cloud. On those regions where the observed polarization angle is constant, the polarized spectrum shape suggests heterogenous grain alignment within the cloud.
Overall, the analysis shows the potential of multi-band polarimetry for tracing the 3D structure of magnetic fields, as well as grain alignment.

Keywords: Magnetic Fields, Interstellar Dust, Far-infrared Astronomy, Polarization