Star forming galaxies in a galaxy supercluster

In 2013, I did research in astrophysics with Professor Tracy Webb at McGill. Professor Webb studies cosmological structure formation, which is the science of how large-scale structures grow in the universe.

This field is full of open questions, but the current paradigm is that large-scale structures formed from gravitationally merging small-scale structures. In this hierarchical picture, stars formed earliest. Clusters of stars went on to form the first galaxies, and galaxies eventually merged into galaxy clusters. Today, the largest known structures in the universe are galaxy superclusters, which are clusters of galaxy clusters. Most of them are still in the process of forming.

In the Webb group, I studied a rare galaxy supercluster called RCS2319+00, which consists of three high-mass galaxy clusters. RCS2319 is considered rare because it’s located at redshift z ∼ 0.9, which means it’s about eight billion lightyears away from Earth and we’re seeing it as it appeared eight billion years ago. (The cosmological redshift z describes the extent to which the expansion of the universe stretches light emitted at different distances from Earth.) Since most galaxy superclusters are still forming today, this implies that RCS2319 formed about eight billion years ahead of its time.

My project was to quantify the star formation rates of the brightest infrared galaxies in RCS2319. These “starburst” galaxies can produce hundreds to thousands of stars per year. To do this, I first built a database of galaxies in the supercluster by identifying them in a spectroscopic catalogue of about 200,000 celestial objects. I then matched them with objects in an infrared catalogue covering the same area of the sky. The result was a list of 38 luminous infrared galaxies likely to be members of the supercluster. To calculate their star formation rates, I fit an infrared galaxy model to each of their spectra. All in all, I estimated that RCS2319 was forming about 2100 solar masses per year.

If you’re interested in learning more, feel free to check out my undergraduate physics thesis. I also presented a poster on this research at the 2014 Canadian Undergraduate Physics Conference in Kingston, Ontario.