Infrared spectropolarimetry of the Galactic Centre: magnetic alignment in the discrete sources

Abstract

We present the results of 8–13 μm spectropolarimetric observations of Galactic Centre sources. All the sources show interstellar polarization due to absorption by aligned silicate grains and these grains appear to be spatially separated along the line-of-sight from those which produce the polarization at shorter wavelengths. The line of sources IRS 1, 10, 5 and 8 comprising the northern arc all show strong intrinsic polarization due to thermal emission from aligned grains of amorphous silicate-like material. This polarization is very uniform among these sources with position angle closely normal to the line of the arc. It is shown that the data are inconsistent with grain alignment due to streaming, but favour alignment by a strong magnetic field >10 mG directed along and linking the northern arc of sources. A field of this magnitude will have significant influence on the structure and evolution of sources in the Galactic Centre, and some possible implications are discussed.