UH Hilo, Canada-France-Hawaiʻi Telescope, and Université Laval Collaborate to Simulate Galaxy Collision

Astronomers studying a slow-motion collision between two galaxies have uncovered a massive burst of new star formation. The new study co-authored by Dr. R. Pierre Martin, an astronomer at UH Hilo, takes a look at the interaction between two spiral galaxies, NGC2207 and IC 2163.

A new study co-authored by Camille Poitras, PhD student at Université Laval, Dr. R. Pierre Martin of the University of Hawaiʻi at Hilo (UHH), and colleagues at Université Laval in Québec, Canada, simulates the past, present, and future of a collision between two spiral galaxies. The authors relied on the “amazing” data from the Canada-France-Hawaiʻi Telescope (CFHT)’s Fourier transform spectrograph SITELLE — the only instrument of its kind in the world, based right here in Hawaiʻi. Discoveries like these particularly speak to the importance of undergraduate research experience, international collaboration, and building longstanding relationships that allow these discoveries to occur.

This study is a culmination of over two decades of collaboration between researchers at CFHT and Laval. R. Pierre Martin, the principal investigator, former astronomer, and director of science operations at CFHT, who is now the chair of the Department of Physics and Astronomy at UH Hilo and director of the UHH Educational Observatory. He and Laurent Drissen, the third author listed in the study, actually first met on Maunakea. “Maunakea brought us together as a research team. It is a very special place for Hawai‘i and for the world. There are many researchers worldwide who really, deeply care about Maunakea,” said Pierre.

Their ongoing work together began with a dream — to build an instrument capable of observing all sorts of galaxy phenomena and behavior over a much larger field of view than was previously possible. Perhaps even large enough to observe multiple galaxies in their entirety. After many years of incredibly hard work led by Laurent, the instrument came to fruition in 2015 — the Fourier Transform spectrograph SITELLE, installed at CFHT. “It’s a remarkable instrument,” said Pierre. “Among all the galaxies we have been studying since, notably under a large program called SIGNALS, I've also wanted to study this specific galaxy collision for a long time. But we never had the right instrument until now.” With its exceptional capabilities, SITELLE was able to capture the entirety of both galaxies at once, allowing researchers to model the full extent of the collision in dazzling detail.

The collision in question began ~440 million years ago, between two large galaxies called NGC 2207 and IC 2163. Since then, the two have slammed into each other, pulled apart, and come back together multiple times. Eventually they will merge into one, and their ancient shapes and characteristics will be rendered unrecognizable.

“All galaxies collide in their lifetimes. They are very social beings!” Pierre explained. The immense gravity pulls galaxies towards one another, and these interactions range from small ones — like when the Milky Way has eaten up small galaxies in the past — to completely transformative. The research team hoped to not only try to understand the collision but also how it has altered both galaxies and how it may continue to in the future.

This particular galaxy collision was first simulated 20 years ago by other investigators. The team used these early models to create a starting point for their own simulation, which was carried out using advanced, high-performance computer simulations based at Université Laval in Québec. They ran hundreds of simulations, using the high-quality data from the SITELLE spectrograph to model the shape, gas distribution, rate of star formation, and the motions of stars and gases throughout the galaxies with great accuracy. “This is the most sophisticated simulation to do this in the world right now,” Pierre said. By simulating both how the galaxies would have evolved individually as well as simulating collisions until they finally matched our contemporary observations, the team was able to create an impressive model that spans more than 600 million years – from their first interaction 440 million years ago to predicting the galaxies’ behavior more than 200 million years into the future.

Making those predictions can be extremely difficult, as every collision is unique. “It’s as if you said, ‘model a car crash,’” explained Pierre. The number of variables — speed, angle, the makeup of elements in the galaxies — means there is an almost infinite range of what galactic collisions can look like. But studying one in detail, like NGC 2207 and IC 2163, gives us a better idea of what could happen in the future, including for our own galaxy, the Milky Way. When galaxies collide, it can have a big ripple effect, literally, which redistributes the gases and chemical elements within the galaxies. These gas cloud collisions can often trigger more new star formations, as the increased mixing of gases between the two galaxies introduces new elements that may have been missing. This has large consequences for the galaxy’s evolution as well as kinds of new planets that then form within the galaxy.

Read the full story at Maunakea Observatories, Hawaii News Now (HNN), and Maui Now.

Read the journal article at Monthly Notices of the Royal Astronomical Society.