Mopra came to Nagoya university in Japan this week. The occasion was a workshop on the centre of our Milky Way galaxy. Nagoya, home to the Nanten2 telescope in Chile featured in earlier blog entries, are also big users of Mopra. The reason is simple: Mopra and Nanten2 have very complementary capabilities and can work together well in charting the molecular medium of our Galaxy. Nanten is smaller, but can work at higher frequency, and is capable of mapping larger regions than Mopra, albeit with lower resolution.
The centre of the Galaxy is of especial interest to millimetre-waves astronomers, for it also hosts the largest concentration of molecular gas in our Galaxy – the Central Molecular Zone (or CMZ) – home to around 100 million solar masses of molecules in the inner few hundred parsecs of our Galaxy. Mopra has been engaged in a program to map the distribution of a range of exotic molecules that are found in the CMZ – where they are found extended over several degrees of sky. The molecular gas here is denser, hotter and more turbulent than the molecular clouds found in the spiral arms of our Galaxy, and presents a very different environment for study. It is also the only galactic nucleus we can see up close, so the CMZ provides a kind of standard candle against which we can compare the unresolved emission from other galactic nuclei against, in the hope of understanding them.
We have used the wide band spectrometer to simultaneously map the emission from these molecules, a unique capability that Mopra has. In two spectral ranges, between 85-93 GHz in the 3mm waveband, and 42-50 GHz in the 7mm waveband, the spectrum is especially rich, and Mopra has mapped the distribution of about 50 different species of molecules and atoms. We are now engaged in a new program to map the CO distribution over the inner 5×2 degrees of the Galaxy, a particularly challenging project due to the extremely broad lines, extending over ~500 km/s in velocity. Rebecca Blackwell, a PhD student at Adelaide, is leading this program, where the data is being combined with wider view, but lower resolution Nanten data, as we seek to understand its dynamical motions and orbital trajectories. It appears that gas is continually being fed into the CMZ, where it gets converted into the most luminous stellar clusters found in the Galaxy.
The CMZ contains a diverse range of astrophysical phenomena, from cold gas and the formation of stars, to hot plasma and the most energetic particles in our Galaxy, all centred on a black hole which weighs around 4 million times the mass of our Sun. Particularly intriguing is the close relation between gamma rays and molecular gas – for their distributions are remarkably similar, given that they represent some of the highest and lower energy phenomena that exist in nature, respectively. The key appears to be that the gamma rays are produced when extreme energy cosmic rays collide with nuclei in space, and the latter are most common in molecular clouds. So mapping the molecular gas distribution in the coldest regions of space is essential for understanding the acceleration mechanisms behind the highest energy particles we know about! With the building of the next generation gamma ray telescope about to begin – the Cherenkov Telescope Array (CTA) – the Mopra data will be invaluable. For it will provide an image of the regions where these collection occur of comparable resolution to that which CTA will make of the gamma rays that are then produced!
Professor Yasuo Fukui, director of the Nanten2 telescope, explaining the linkages between molecular clouds and gamma rays in the Nagoya university science magazine “philosophia”.
But the final mystery to be tackled at Nagoya wasn’t astronomical at all, it was location of Craig. Craig is a mythical figure, responsible for one of the most amazing new telescopes of recent times, the terahertz frequency HEAT telescope on the top of the Antarctic plateau. HEAT is mapping the element carbon across the plane of our Galaxy, in a project with close connections to the CO survey we are undertaking with Mopra. But Craig is an elusive person, almost impossible for his colleagues to find, so many projects is he involved with. The mystery of his location was solved in Nagoya with the discovery of Craig’s cafe sited right next to the building our galactic centre workshop was held in, and home to the best cappuccino in the university. Craig must be leading a double life as both a barista and an astronomical instrument builder!