Bright prospects: Comparing the H Survey with large-scale radio continuum emission

Comparisons

The essential objective of comparisons between radio and H emission is to determine as much as possible about the presence, morphology and physical conditions of the ionised gas.

However, although the limiting emission measures of the Parkes and H surveys are similar, there are several significant differences between the two types of emission in general, and between these two surveys in particular. A few of the more important similarities and differences will be noted now.

First, we reiterate that both H and radio continuum emission are tracers of ionised gas, with temperatures of several times  K. Both types of surveys can therefore assist in detailing the structure and morphology of ionised regions, although the low resolution of our Parkes observations restricts the radio data to investigations on scales of 10 arcmin or greater. Hence, the H survey can provide high-resolution information on many objects identified from the radio data. Note also that the radio continuum, unlike optical observations, is not affected by extinction.

Second, in contrast to H , the radio continuum contains large quantities of non-thermal emission. This can be of benefit when investigating certain objects (such as supernova remnant shocks) but can complicate studies of large-scale, diffuse thermal emission.

Third, the comparison of H with radio continuum data can assist in determining line-to-continuum ratios, which allows the temperature of the ionised gas to be estimated.

© Copyright Astronomical Society of Australia 1997