NRC scientist leads largest-ever survey of our sister galaxy

Victoria, BC – An international team of astronomers led from the National Research Council Herzberg Institute of Astrophysics (NRC-HIA) has discovered that our near cosmic neighbour, the Andromeda Galaxy, is swallowing smaller galaxies as it continues to grow. Results published this week in the science journal Nature show the discovery of giant structures in its outer parts, relics of smaller galaxies that have already been absorbed by Andromeda. The finding has come to light from the broadest and deepest image of a galaxy ever made, spanning a volume with a diameter nearly 1,000,000 light years around Andromeda.

The Andromeda Galaxy is the nearest large galaxy visible to the naked eye from the Northern Hemisphere, more than 2,500,000 light years from the Milky Way. “That we are finding streams and structures over the entire survey area is a startling demonstration of the vast size of this ‘typical’ galaxy,” notes Dr Alan McConnachie of NRC-HIA, lead researcher on the project. “Until a few years ago, no one expected to find anything this far from the centre of a galaxy. But Andromeda is showing us that galaxies are much bigger than we originally thought.”

Galaxies are large collections of stars and other matter that are held together by gravity. Theory holds that they evolve and grow by absorbing smaller galaxies over time. One of the major scientific themes that drives astronomy is the quest for the origins of structure in the universe: the formation of planets, stars, and galaxies, as well as the geometry and fate of our universe. The results published today set the stage for a more detailed reconstruction of Andromeda’s formation, a process that appears to be continuing to this day.

According to Dr Thomas Puzia, a researcher at NRC-HIA, initial results indicate that Andromeda is interacting with its close companion, the Triangulum Galaxy. “Ultimately, these two galaxies may end up merging together completely,” says Dr Puzia. “Ironically, galaxy formation and galaxy destruction seem to go hand in hand.”

Dr McConnachie leads the survey team, which includes NRC astronomers alongside university-based researchers from across Canada, as well as colleagues in Australia, France, Germany, the UK and the US. Their findings appeared on September 3 in Nature. The survey, which began in 2008 and continues through 2011, uses the Canada-France-Hawaii Telescope (CFHT), in which NRC is a partner, and CFHT’s MegaCam/MegaPrime digital camera, designed and built by the NRC Herzberg Institute of Astrophysics in Victoria.