The MSSSO Wide Field CCD H Imaging Survey

Comparison with MOST Galactic Plane Images

Continuum emission at 843 MHz is dominated by nonthermal processes. H is a tracer of thermal emission. A comparison of the two surveys will give insights into the distribution of the different mechanisms. The MOST Galactic Plane survey has a resolution of (Green 1996) while the H images have a resolution of 12'' per pixel.

Because the radio emission is not affected by dust extinction, the MOST images contain many extragalactic objects, in particular background galaxies which are seen as unresolved sources. These radio galaxies will not be seen in H. However, gas-rich spiral galaxies with significant star formation could well appear as (mostly unresolved) H sources. The vast majority of the H emission will be from our Galaxy, in the form of extended filaments and clouds. Supernova remnants also characteristically have filamentary structure, in this case produced by the nonthermal synchrotron process. This emission is produced from the interaction of the expanding shock front from the supernova explosion with interstellar and circumstellar material. Studies of nearby supernova remnants such as Vela (eg Bock 1997) and the Cygnus Loop (eg Straka et al 1986) show large variations in the correspondence between the H and radio filaments. The results from the present survey will be used to further investigate this question. Some discussion of the expected correlations are given in Cram et al (1998). The presence of shocked lines of [SII] and [OIII] may help to discriminate between the different excitation mechanisms.

© Copyright Astronomical Society of Australia 1997