The Galactic Centre region

We present a broadband spectropolarimetric survey of 563 discrete, mostly unresolved radio sources between 1.3 \& 2.0 GHz using data taken with the Australia Telescope Compact Array (ATCA). We have used rotation measure synthesis to identify Faraday complex polarized sources --- i.e. objects whose frequency-dependent polarization behaviour indicates the presence of material possessing complicated magnetoionic structure along the line of sight (LOS). For sources classified as ...

With the Westerbork Synthesis Radio Telescope (WSRT), multi-frequency polarimetric images were taken of the diffuse radio synchrotron background in a region centered on (l,b) = (161,16). The observations were done simultaneously in 5 frequency bands from 341 MHz to 375 MHz, with 5 arcmin resolution. Ubiquitous structure on arcminute and degree scales in the polarized intensity and polarization angle, combined with no observed structure in total intensity, indicates that the s...

The magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission o...

We present a detailed examination of the relationship between the magnetic field structures and the variations in Faraday Rotation across PKS1246-410, a radio source in the Centaurus cluster of galaxies, using data from Taylor, Fabian and Allen. We find a significant relationship between the intrinsic position angle of the polarization and the local amount of Faraday Rotation. The most plausible explanation is that most or all of the rotation is local to the source. We sugges...

The amplitude of the magnetic field surrounding the Galactic Centre (GC) on large scales (> 100 pc) has been uncertain by two orders of magnitude for several decades: different analyses report fields as weak as ~6 microG on the one hand and 1 mG on the other. Here I report on our recent work which shows that the field on 400 pc scales has a firm lower limit of about 50 microG. To obtain this result we compiled existing (mostly single dish) radio data to construct the spectrum...

Regular magnetic field structures can be derived from the Faraday rotation measures (RM) of polarized background sources observable at 1.4 GHz with the SKA. At lower frequencies ($<250$ MHz) polarimetry of radio sources with the Low Frequency Array (LOFAR) will allow the investigation of extremely small RM, to detect and map weak regular fields in halos and outer parts of spiral galaxies, and in the interstellar and intergalactic medium. Very little is known yet about the num...

The amplitude of the magnetic field near the Galactic Centre has been uncertain by two orders of magnitude for several decades. On a scale of approximately 100 pc fields of approximately 1000 microG have been reported, implying a magnetic energy density more than 10,000 times stronger than typical for the Galaxy. Alternatively, the assumption of pressure equilibrium between the various phases of the Galactic Centre interstellar medium (including turbulent molecular gas; the c...

The magnetic field within a few hundred parsecs of the center of the Galaxy is an essential component of any description of that region. The field has several pronounced observational manifestations: 1) morphological structures such as nonthermal radio filaments (NTFs) -- magnetic flux tubes illuminated by synchrotron emission from relativistic electrons -- and a remarkable, large-scale, helically wound structure, 2) relatively strong polarization of thermal dust emission fro...

A514 contains six extended and polarized radio sources located at various projected distances from the cluster center. Here we present a detailed study of these six radio sources in total intensity and polarization using the Very Large Array at 3.6 and 6 cm. Since the radio sources sample different lines of sight across the cluster, an analysis of the Faraday Rotation Measures (RMs) provides information on the strength and the structure of the cluster magnetic field. These so...

We measured the linear polarization of Sagittarius A* to be 7.2 +/- 0.6 % at 230 GHzusing the BIMA array with a resolution of 3.6 x 0.9 arcsec. This confirms the previously reported detection with the JCMT 14-m antenna. Our high resolution observations demonstrate that the polarization does not arise from dust but from a synchrotron source associated with Sgr A*. We see no change in the polarization position angle and only a small change in the polarization fraction in four o...