Results from the 7-mm workshop

The frequency coverage of the Compact Array currently has a rather large gap between 25 and 50 GHz. Since external funding has recently become available to build receivers for this "7-mm" band, a workshop was held on 31 May to explore its scientific opportunities. On sub-galactic scales, the 7-mm band appears optimal to study the poorly constrained theory of the formation of high-mass stars, via observations of radio emission from jets and Ultra-Compact HII regions which signpost the earliest phases in stellar lives. In the later stages of stellar evolution, SiO masers are common in low-intermediate mass stars, being visible throughout the Milky Way and are excellent tracers of galactic dynamics. As an example of using 7-mm observations to study the final stages of stellar evolution, it was reported that the study of SN1987A would profit considerably from the upgrade. It was shown that a vast number of molecular lines exist in this band, many of which are known as valuable probes of density and temperature such as methanol, whilst others are still unexplored or entirely unknown.

In extragalactic astronomy, 7-mm VLBI observations are currently the best compromise of sensitivity and resolution to study AGN cores and jets. International collaborations with KVN, VERA and VLBA appear feasible, as well as Australian-only VLBI observations using the Compact Array, Mopra and Tidbinbilla. On a cosmological scale, the 7-mm upgrade would be invaluable for observations of CO at high redshifts. At almost any redshift between 1.5 and 8, the 7-mm band will not only cover a CO transition of the object, but these transitions would be the easiest to detect with the Compact Array. Furthermore, the 7-mm band would provide data from lower transitions, which are essential when star formation in galaxies at high redshifts is to be modelled. On the largest scale, it was suggested that galaxy clusters could be observed via the Sunyaev-Zeldovich effect, which is a redshift-independent measure of cluster mass. The workshop was widely regarded as a success, and the new ideas will significantly improve the science document for the upgrade. Thanks to all the speakers and participants!

Enno Middelberg
Enno.Middelberg@csiro.au