CFHT, Current Image of the Week


July 31st, 2000

The COMA cluster of Galaxies

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The COMA cluster of galaxies

Credit: A. Mazure , C. Adami & C. Savine
Laboratoire d'Astrophysique de Marseille, France

(This image has been obtained in the framework of a large collaboration involving:
A. Mazure, C. Savine, C. Adami (Marseille), M. West (UH), J.P. Picat, G. Mathez, R. Pello (Toulouse), M. Gregg (UC Davis), J.C. Cuillandre (CFHT), C. Conselice, J. Gallagher (Madison), M.P. Ulmer (NU))

The distribution of matter in the Universe is highly structured. Stars gather in galaxies. Galaxies themselves are grouped in clusters. Clusters of galaxies are the largest structures in dynamical equilibrium in the Universe. They are composed of dark matter, hot gas and galaxies. Such systems act as very large cosmological laboratories. In this harsh environment, galaxies are subject to many abuses: they suffer stripping by the hot intracluster medium, tidal disruption by the cluster gravitational field, destructive encounters with neighbors.

The Coma cluster is a prototypical rich cluster of galaxies, with over a thousand members known. We present two enlargements of an optical image of the core of the Coma cluster recently obtained with the CFH12K camera. It represents one of the deepest view of Coma on such a large field (two times 30 arcmin x 40 arcmin). Most of the objects in these pictures are galaxies, mostly ellipticals and SO. The two luminous central giant elliptical galaxies, NGC 4889 (left) and NGC 4874 (right), are clearly identified in the large scale mosaic . The two enlargements shown here reveal interesting features of this image: (Bottom Right) a close-up on MGC 4874 and a tidal tail (field of view shown: 8'x8'), resulting probably from the disruption of small galaxies in the gravitational field of the central ellipticals, (Bottom Left) an example of the swarm of faint galaxies detected down to R=25 both in the cluster and in the background (field: 4'x4').

Such images associated with spectroscopy, allow to understand the kinematical properties of these large structures, and therefore to study the mass distribution of the galaxies in these systems, especially at the low mass end, a key parameter for cosmological studies. Other important issues that can be addressed are: the structure of the line of sight, the tidal disruption efficiency in the core of the cluster, chemical abundances of the galaxies, and study of the diffuse light.

Technical description:

The image presented is a mosaic of 2 CFH12K fields in the R band taken on February 6th and 7th, 1999 and April, 9th and 10th, 2000. Exposure time is 1 hour. The seeing was around 0.9 arcsec. The pixel scale is 0.2 arcsec. For the top mosaic an 8x8 pixel binning has been used. North is up, East to the left.

next week: To be announced shortly

editors: François Ménard, Jean-Charles Cuillandre & Catherine Dougados
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CFHT is funded by the Governments of Canada and France, and by the University of Hawaii.