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Galactic archaeology using the MegaCam

Images from the MegaCam camera developed at the Irfu reveal previously unexpected, extended structures within a group of galaxies called Stephan's Quintet. These structures demonstrate long-standing interactions between galaxies, indicating that the group is much older than models have predicted.
Published on 16 February 2018

Located 340 million light-years from us, Stephan's Quintet is an exceptional arrangement of five very close galaxies. Because of this, it is a well-studied case study for understanding the collective evolution of galaxies: slow collisions, the formation of "tidal tails", stellar formation flare-ups, etc. Under the effect of gravity, galaxies disintegrate or merge according to their successive interactions until they form a single giant elliptical galaxy.

The images provided by the MegaCam reveal for the first time a large number of galactic and extragalactic structures around the Quintet, some of which are quite extensive and not very bright. In particular, a red halo made up of old stars and centered on one of the Quintet's elliptical galaxies indicates that this particular galaxy has been interacting with the other four for a very long time, whereas astrophysicists had believed it to be inert or a recent arrival. Thus, the Quintet would be much older than the researchers had previously thought.

These results are the outcome of a collaboration between the Observatory of Strasbourg, the Irfu and the Lund Observatory (Sweden). They are based on an image originally intended for a Canada-France-Hawaii Telescope (CFHT) calendar.

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