Magnetic field in the Galactic Centre: Rotation Measure (RM) observations of extragalactic sources

Subhashis Roy1, A. Pramesh Rao1, Ravi Subrahmanyan2

1 National Centre for Radio Astrophysics (TIFR),
Pune University Campus, Post Bag No.3, Ganeshkhind, Pune 411 007, India.
2 ATNF, P.O. Box 76, Epping, NSW 2121, Australia

E-mail contact: roy@ncra.tifr.res.in

Magnetic fields can be strong enough to have a significant influence on the dynamics and evolution in the central region of our Galaxy. However, other than the central 200 pc region, the magnetic fields of the inner 5 kpc region of the Galaxy have not been observationally constrained. Therefore, we have studied Rotation Measure (RM) towards suspected extragalactic sources seen through the central l x b = 12deg x 3.6deg region of our Galaxy with the ATCA and VLA. A total of 65 sources were observed, out of which 45 sources were found to be polarised. We have estimated the RM towards these sources. The estimated RM towards the sources located within 1.5 degrees from the Galactic plane are quite high, about 1000 rad m^-2. RM towards most of the sources are estimated to be positive and no significant variation of RM with the galactic longitude could be detected. This rules out any axisymmetric model of the magnetic field near the central region of the Galaxy. We discuss possible implications of these results.