Observational Results

To illustrate the capabilities of the instrument we have included some observing highlights from the instruments first few years of operation. These data were obtained at the Anglo-Australian 3.9-m Telescope (AAT) and United Kingdom Infrared 3.9-m Telescope (UKIRT).

As an example of the instrument's capabilities, figures 5 - 8 show diffraction limited (PSF FWHM = 0.7 arcseconds) 10 m images of the Galactic Centre (Fig. 5), Carina (Fig. 6), NGC 1068, a Seyfert galaxy (Fig. 7), and a bipolar proto-planetary nebula Mz-3 (Fig. 8). Superimposed on three of the images are polarization vectors, which indicate the direction of the local magnetic field, while the length of the vector indicates the polarization magnitude.

 
Figure 5: A diffraction limited image of the Galactic Centre at 12.5 m. The vectors indicate the direction of the magnetic field, and the magnitude of the polarization.

 
Figure 6: Carina at 12.5 m. Image reconstruction (using the pixon-based method) has been employed to produce an effective image resolution of around 0.3 arcseconds, revealing interesting loops near the homonculus core. In this source grain alignment maybe enhanced by streaming, but the polarization vectors still indicate the direction of the local magnetic field.

 
Figure 7: Broad band 10 m polarimetric image of the Seyfert galaxy NGC 1068. This is the only mid-infrared polarimetric image of a galaxy ever obtained. It shows polarized emission from obscuring dust (magnetic field direction normal to this), plus dilution of the polarization near the galaxy core, probably caused by emission from the active nucleus.

 
Figure 8: Mz-3 at broad band 10 m. Here we see bright bi-polar lobes which are radiatively heated by the central source.

Polarization at these wavelengths is most often due to emission or absorption from aligned dust grains. In the Galactic Centre the grains are aligned by the ambient magnetic field, presumably by a modified Davis-Greenstein mechanism, and the emitted direction of polarization is at right angles to the field: here the displayed vectors have been drawn orthogonal to the polarization and hence give the field direction. These results confirm and extend earlier work at UKIRT (Aitken et al., 1991) using the GSFC camera with a smaller array, but here the area coverage is greatly increased (from a 15 15 arcsecond region to a 30 45 arcsecond region) in roughly the same observing time. Details of these observations are presented in Aitken, Smith, Moore & Roche (1996).

Due to the extremely high signal-to-noise ratio obtained for the polarimetric image of Carina we have been able to employ pixon-based image reconstruction to produce an effective image resolution of around 0.3 arcseconds. The reconstructed image shows interesting loops near the core of the source. The magnetic field structure seen here may be the compressed, pre-existing field about Carina at the time of the 1843 eruption, or the diluted remnant of the stellar field, but it seems more likely that it results from a toroidally magnetized accretion disk in which we suggest the explosion of 1843 occurred. This case is argued in detail in Aitken et al. (1995), and Smith et al., (1995).

The image of NGC 1068 is the only mid-infrared polarimetric image of a galaxy ever obtained. The image data are very similar to that of Braatz et al. (1993 ) and Cameron et al. (1993). It shows polarized emission from obscuring dust, plus dilution of the polarization near the galaxy core, probably caused by emission from the active nucleus. Details of these observations will be presented in Lumsden et al. (1996).

In Mz-3 we see bright bi-polar lobes which are radiatively heated by the central source. These observations are presented in Quinn et al. (1996).

© Copyright Astronomical Society of Australia 1997