Galaxies are often found in clusters, which contain many ‘red and dead’
members that stopped forming stars in the distant past. Over billions of
years, galaxy clusters build up structure in the universe - merging
with adjacent clusters. When this happens, there is a huge release of
energy as the clusters collide. The resulting shock wave travels through
the cluster like a tsunami, but until now there was no evidence that
the galaxies themselves were affected very much.
An international team of astronomers, led by Andra Stroe of Leiden
Observatory and David Sobral of Leiden and the University of Lisbon
observed the merging galaxy cluster CIZA J2242.8+5301, nicknamed the
‘Sausage’. They used a custom-designed set of narrow-band filters
mounted on the Wide Field Camera on the Isaac Newton Telescope, the
multi-object spectrograph, Autofib-2, on the William Herschel Telescope,
and some other telescopes in Hawaii. They find that far from ‘watching
from the back’ the cluster galaxies were transformed by the shock wave,
triggering a new wave of star formation.
The new work implies that the merger of galaxy clusters has a major
impact on the formation of stars: the shocks lead to turbulence in the
galactic gas which then triggers an avalanche-like collapse, leading to
the formation of very dense, cold gas clouds, which are vital for the
formation of new stars. Star formation at this rate leads to a lot of
massive, short-lived stars coming into being, which explode as
supernovae a few million years later. The explosions drive huge amounts
of gas out of the galaxies and with most of the rest consumed in star
formation, the galaxies soon run out of fuel. The cluster mergers make
the galaxies even more red and dead.
Every cluster of galaxies in the nearby Universe has experienced a
series of mergers during its lifetime, so they should all have passed
through a period of extremely vigorous production of stars. Given that
the shocks will only however lead to a brief (in astronomical terms)
increase in star formation, astronomers have to be very lucky to catch
the cluster at a time in its evolution when the galaxies are still being
`lit up’ by the shock.
More Information
David Sobral, Andra Stroe, William A. Dawson, David Wittman, M. James
Jee, Huub Röttgering, Reinout J. van Weeren and Marcus Brüggen, 2015,
"MC2: boosted AGN and star formation activity in CIZA J2242.8+5301, a
massive post-merger cluster at z = 0.19", MNRAS, 450, 630. Paper.
Andra Stroe, David Sobral, William Dawson, M. James Jee, Henk Hoekstra,
David Wittman, Reinout J. van Weeren, Marcus Brüggen and Huub J. A.
Röttgering, 2015, "The rise and fall of star formation in z~0.2 merging
galaxy clusters", MNRAS, 450, 646. Paper.
"Giant cosmic tsunami wakes up comatose galaxies", RAS press release, 24 April 2015.
Contact:
Javier Méndez (Public Relations Officer)
Source: Isaac Newton Group of Telescopes
