Magnetic Field at the Galactic Centre from Multi-Wavelength Dust Polarization

We have mapped the magnetic field (B-field) for a region of about 30 pc around the centre of our Galaxy, which encompasses the circumnuclear disk (CND), the mini-spirals, and the 20 km s⁻¹ and 50 km s⁻¹ molecular clouds, using thermal dust polarization observations obtained from SOFIA/HAWC+ and JCMT/SCUPOL. We decompose the spectra of ¹²CO (J=3→2) transition from this region into individual clustered cloud components and find the polarization observed at different wavelengths might be tracing completely different layers of dust along the line-of-sight (LOS). We use modified Davis-Chandrasekhar-Fermi methods to estimate the B-field from the observations. From our analysis we find the mean strength of the plane-of-sky B-field (B_POS) of the CND and the mini-spirals, probed at 53 μm to be of the order of ~2 mG. The magnetic field is lowest close to the Galactic Centre, in the region of the ionized mini-cavity within the CND with B_POS<1 mG, and increases outwards. However, the longer wavelength polarization at 216 μm appears to come from a dust layer that is cooler and behind the CND and has a stronger B-field of about 6 mG. The B-field has the least strength along the Eastern Arm of the mini-spiral, which is also the only region with MA>1 and a mass-to-flux ratio of λ1. The similarity between the B_POS estimates of the 53 μm and 850 μm observations might indicate them originating from the same depth along the LOS, mostly from the CND and its foreground cloud features, including the negative-longitude extension.