The Galactic centre region

Abstract

We have observed the central 450 region of the Galaxy at 620 MHz band of the Giant Metrewave Radio Telescope (GMRT) in radio continuum, and measured the polarisation properties of 64 small diameter background extragalactic sources seen through the -6o < l < 6o, -2o< b < 2o region with the Australia Telescope Compact Array (ATCA) and the Very Large Array (VLA). Our 620 MHz observations show that Sgr A* is located behind the HII region Sgr A West. Using the ATCA and the VLA observations, we measured the Faraday rotation measure (RM) of the polarised sources. The measured RMs are mostly positive, and show no reversal of sign across the rotation axis of the Galaxy. This rules out any circularly symmetric model of magnetic field in the region. We estimate the magnetic field strength in the region to be ~ 10mu G, which raises doubts against an all pervasive mG field in the central few hundred pc of the Galaxy