The Galactic Centre region

The Southern Galactic Plane Survey (SGPS) is a 1.4 GHz radio polarization and HI survey in a large part of the inner Galactic plane at a resolution of about an arcmin. Depolarization and Faraday rotation of polarized radiation from diffuse Galactic synchrotron emission, pulsars, and extragalactic sources can be used to infer information about the strength and structure of the Galactic magnetic field. Here, we discuss science results of the polarization data from the SGPS. We ...

New observations of Sgr A have been carried out with the VLA using the broadband (2 GHz) continuum mode at 5.5 GHz, covering the central 30 pc region of the RBZ at the Galactic center. Using the MS-MFS algorithms in CASA, we have imaged Sgr A with a resolution of 1", achieving an rms 8 $\mu$Jy/beam, and a dynamic range 100,000:1.The radio image is compared with X-ray, CN emission-line and Paschen-$\alpha$ images obtained using Chandra, SMA and HST/NICMOS, respectively. We dis...

The centre of our Milky Way harbours the closest candidate for a supermassive black hole. The source is thought to be powered by radiatively inefficient accretion of gas from its environment. This form of accretion is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which it can be fed. However, the magnetization of the gas, a crucial parameter determining the structure of the accretion flow, ...

Magnetic fields in the Milky Way are present on a wide variety of sizes and strengths, influencing many processes in the Galactic ecosystem such as star formation, gas dynamics, jets, and evolution of supernova remnants or pulsar wind nebulae. Observation methods are complex and indirect; the most used of these are a grid of rotation measures of unresolved polarized extragalactic sources, and broadband polarimetry of diffuse emission. Current studies of magnetic fields in the...

We have carried out observations of the newly-discovered magnetar in the direction of Sagittarius A* using the Australia Telescope Compact Array in four frequency bands from 4.5 to 20 GHz. Radio pulsations are clearly detected at all frequencies. We measure the pulsar's dispersion measure to be 1650 +/- 50 pc/cm^3, the highest of any of the known pulsars. Once Faraday rotation has been taken into account, the pulse profile is more than 80% linearly polarized at all frequencie...

Sub-arcsecond radio continuum observations of the Galactic center region at $\lambda$6 and 2cm reveal a 0.5$^{\prime\prime}$ diameter source with a shell-like morphology. This source is linearly polarized at a level of 16% at $\lambda$6cm and has a steep nonthermal spectrum with spectral index 1.6 between $\lambda$6 and 2 cm. The distance to this source is not known but the large rotation measure value of 3000 rad m$^{-2}$ suggests that G359.87+0.18 is likely to be located in...

We report the detection of polarized emission in the vicinity of the Galactic center for 158 positions within eight different pointings of the Hertz polarimeter operating on the Caltech Submillimeter Observatory. These pointings include positions 2 arcminutes offset to the E, NE, and NW of M-0.02-0.07; positions to the SE and NW of the 20 km/s cloud (M-0.13-0.08), CO+0.02-0.02, M+0.07-0.08, and M+0.11-0.08. We use these data in conjunction with previous far-infrared and submi...

We present a large-scale view of the magnetic field in the central 2deg * 2deg region of our Galaxy. The polarization of point sources has been measured in the J, H, and Ks bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m telescope IRSF. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we obtain polarization originating from magnetically aligned dust grains in the central few-hundred pc of our Galaxy. We fi...

We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) towards 641 polarized extragalactic radio sources in the Galactic longitude range 100-117 degs, within 30 degs of the Galactic plane. For |b| < 15 degs, we observe a symmetric RM distribution about the Galactic plane. This is consistent with a disk field in the Perseus arm of even parity across the Galactic mid-plane. In the range 15<|b|<30 degs, we ...

The scattering diameters of Sgr A* and several nearby OH masers (~ 1" at 1 GHz) indicate that a region of enhanced scattering is along the line of sight to the Galactic center. The scattering diameter of an extragalactic source seen through this scattering region is larger by the ratio (Sun-GC distance)/(GC-scattering region separation). This ratio could be a factor of a few, if the scattering region is far from the GC and only a random superposition with it, to more than 100...