Astronomy Colloquium

Dense molecular gas is considered to be the fuel for star formation in galaxies. To understand the formation of molecular gas, the gravitational collapse of the dense gas into stars and the energetic impact of young massive stars on the ambient clouds in detail, it is therefore indispensable to accurately measure its physical properties such as density and temperature. The transitions of ammonia, the most abundant top-heavy molecule, can be utilized as an easy-to-use thermometer for this important gas phase. Over the last few years, a new generation of 1cm receivers at ATNF and other telescopes has been commissioned which enables astronomers to exploit this peculiar feature of ammonia in far more objects than before. In this talk, I will present results from extensive ammonia observations toward the Galactic Center, nearby starburst and ultraluminous-infrared galaxies, the Magellanic Clouds, and gravitational lenses.