A cataclysmic galactic collision has produced impressive – but transient – arcs of flowing gas and new stars visible with the Atacama Large Millimetre Array (ALMA). The unusual arcuate shape of the starburst region resembles an eyelid.
ALMA was used to track carbon monoxide in the spiral galaxy IC2163, which is interacting with NGC2207. The gas picks out arcuate features to the north and south of the inner spiral, along which there is also intense star formation. The CO in these outer curves of IC2163 is moving inwards at more than 100 km s–1. In the inner part of the galaxy, the motion becomes more chaotic and the gas flow decelerates and aligns with the rotation of the galaxy. At the same time, the gas becomes significantly denser; the eyelids mark strong shocks within the gas triggering star formation, something predicted by models of galaxy interactions. Their existence is likely to be ephemeral, lasting perhaps a few tens of millions of years. This grazing interaction is probably the start of a long-lived interaction between galaxies that will probably result in a merger.
“What we observe in this galaxy is very much like a massive ocean wave barreling toward shore until it interacts with the shallows, causing it to lose momentum and dump all of its water and sand on the beach,” said Bruce Elmegreen, a scientist with IBM’s T.J. Watson Research Center in Yorktown Heights, New York, and co-author of the paper in the Astrophysical Journal.
This image is published in the December 2016 issue of Astronomy & Geophysics.