Molecular clouds are responsible for much of the evolution in the Universe, including starbirth, galaxy mergers, and the fueling of active galactic nuclei. Unfortunately, this gas is mostly molecular hydrogen, which does not radiate easily, and so observations must rely on tracer molecules that are more easily detected, the commonest of which is carbon monoxide (CO). However, in the most energetic regions, changes in cloud chemistry mean that other molecules may be better tracers. Single-dish spectra of nearby starburst galaxies show that global chemical differences among galaxies can be significant, which calls into question the use of CO, or, indeed, any other single molecule as a tracer of molecular clouds and gas mass. This project will focus on the chemical properties of the centers of the closest spiral galaxies, where giant molecular clouds can be resolved in line images, studying at least seven molecules and looking for correlations, trying to find simple characterizations of the cloud chemistry.
This work on the chemical imaging of galaxies is the first of its kind. In addition to revealing the astrophysical environments in these galaxies, this research may place constraints on individual chemical reactions, identifying gas-phase and gas-grain chemistry, and working towards the study of many, much more distant, galaxies with future millimeter array instruments.
