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SLOW MOTION
MERGERS IN GALAXY CLUSTERS PROVIDE CONDITIONS TO TRANSFORM SPIRALS TO SMOOTH
DISKS
Astronomers at
Over the past several billion years
the predominant shape of disc galaxies in clusters has changed from a spiral to
a smooth disk. Theory suggests that this change occurs when two galaxies of
unequal mass merge and gravitational effects pull gas to the galaxies nucleus,
sweeping away the spiral structure and leaving behind a smooth, barren,
thickened disk known as a lenticular galaxy. However, galaxies orbiting in
clusters move at high speeds and in random directions, which should mean that
conditions needed for these slow interactions rarely occur. Instead, multiple
rapid encounters between galaxies, known as 'galaxy harassment', are dominant
but these types of fast encounters cannot easily form the smooth
disks.
The group from Liverpool John Moores
compared eight examples of populations of galaxies falling towards the centres
of galaxy clusters with control samples of galaxies far from the clusters. They
found that the infalling galaxies in the cluster were predominantly distorted in
shape and had a higher than normal rates of star formation. Between a half
and three-quarters of these galaxies were very close by to another galaxy or
appeared to be merging with a companion galaxy, which suggested that
interactions and mergers are more common in galaxies falling into the cluster
than in the control sample.
"Our findings are very exciting
because these results suggest that galaxies are more likely to merge when
falling into a cluster and this may explain why clusters today have so few
spirals and so many lenticular galaxies," said Dr Chris Moss, who will be
presenting the results at the Royal Astronomical Society's National Astronomy
Meeting on the 5th April.
The results suggest the conditions
needed for slow galaxy interactions and mergers are more likely to occur in
galaxies falling into a galaxy cluster compared to the general population of
galaxies outside clusters.
Since infalling of galaxies into
clusters was greater in the past, such interactions and mergers may have
contributed significantly to the transformation of the past population of
cluster spirals to lenticular galaxies in present-day
clusters.
The observations were carried out
over the past several years using the JKT (Jacobus Kapteyn Telescope) and the
Nordic Optical telescope,
NOTES FOR
EDITORS
The 2006 RAS National Astronomy
Meeting is hosted by the
IMAGES:
For images,
see:
http://www.astro.livjm.ac.uk/press/chrismoss.html
1. Cluster: Abell 347, galaxy CGCG
538-043
2. Cluster Abell 426, galaxy CGCG
540-112 = IC 316
3. Cluster Abell 1367, galaxy CGCG
127-012
CONTACTS
Chris
Moss
Astrophysics Research Institute,
Tel: 0151 231
2902
Mobile: 07760 253
992
Fax: 0151 231
2921
E-mail: cmm@astro.livjm.ac.uk
From Wednesday 4th to Friday 7th
April, Dr Moss can be contacted through the
Claire
Thomas
Astrophysics Research Institute,
Tel: 0151 231
2905
Fax: 0151 231
2921
E-mail: cft@astro.livjm.ac.uk
Phil
James
Astrophysics Research Institute,
Tel: 0151 231
2916
Fax: 0151 231
2921
E-mail: paj@astro.livjm.ac.uk