Research Directions


I have many different research directions, but they all centre around the connections between generations of stars.  Carl Sagan gave a pithy summary of what I study: “We are made of starstuff” (from Cosmos).  This line is a short summary of the idea of stellar nucleosynthesis; the idea that the very atoms of which we are made were forged in the nuclear reactions of a previous generation of stars.  Those stars died, returned their material to the gas reservoir in our galaxy (the interstellar medium), and that gas reservoir formed new stars and planetary systems including our Sun. 

Sagan’s quote is a a wonderful little summary of where we came from, and this process of stellar recycling is ongoing today. Given what we think we know about the universe and its origins in a hot Big Bang, this cycle of enrichment must be happening.  But we don’t quite know how this cycle works, and my work aims to develop such an understanding.

From Atomic Gas to Molecular Clouds: Molecular clouds are the sites of all star formation in the local universe.  The process of star formation destroys these clouds meaning that they must be continuously forming to sustain star formation in our Galaxy.  The formation processes of those clouds is unknown.  My group is working to identify those formation mechanisms.  Our primary avenue of research is to study the products in their context: we observe molecular clouds in other galaxy and search for clues

The figure above depicts what happens to the gas in stars when they die, move through the interstellar medium (ISM) and form into new stars.  We astronomers have a pretty good idea of how things work for the blue-coloured connections, but anything with a red connection is not particularly well understood or tested.

From Supernovae to Atomic Gas:  Since dying stars are the sites where elements are returned to the interstellar medium, my research group is searching for the signatures of this effect in the nearby galaxy M33.   The figure at right shows a map of the local enrichment we have made from observations of ionized gas using the Keck telescope.  This project is ongoing and we aim to release a high-resolution, whole-galaxy map of this enrichment pattern.  The pattern of mixing will show how rapidly elements can move between stellar generations and highlight barriers to that process.

about their formation based on changes in the cloud populations.  The figure at left shows molecular clouds (blue dots) overlaid on the atomic gas in a nearby galaxy.  Clouds are only found where there is substantial atomic gas, irrespective of whether there is a spiral arm present, which was some of the first evidence in favour of multiple mechanisms for cloud formation.

From Molecular Clouds to Star Forming Regions: The final aim of my research is to understand how star forming regions form inside molecular clouds.  Some of our research is focused on mapping out the structure of molecular clouds and characterizing it using new tools such as dendrograms.  Most recently, we have been engaged in using statistical methods from the subfield of experimental design to compare numerical models of molecular cloud evolution to actual molecular clouds.  The figures above show observed maps of two molecular clouds (left and centre) and a simulation (right).  We are developing new tools to inter-compare these data sets, which are actually three dimensional data cubes. Given these comparisons, we are able to tune the numerical models to best produce the features of observed star forming regions.

Methods and Directions:  A common methodology running through these projects is studying many objects and combining this with the development of new analysis tools.  My group’s work emphasizes surveys and statistical analyses, where we try to solve problems by observing a large number of systems and test conjectures.  If the existing tools for answering a question are inadequate, we try to develop new ones.  I am keenly interested in similar problems in other fields, and my work uses new developments in high-dimensional image processing, machine learning, dimensionality reduction and image reconstruction. 

Potential Students:  It’s an amazing universe out there and I’d love to teach you more about it.  I am accepting some new students into my research group at the MSc and PhD levels.  To apply, see the Prospective Graduate Students Page and indicate your interest in your statement.  Before you apply, I encourage you to contact me directly beforehand to discuss possible interests and to gauge whether I can support your application. In particular, I am seeking students for work in the PHANGS collaboration.