Abell 851: Are we looking at the beginning of a merging process? |
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| Authors: | E De Filippis S Schindler |
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| Institution: | (1) Astrophysics Research Institute, Liverpool John Moores University, UK;(2) Institut für Astrophysik, Innsbruck |
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| Abstract: | We present an XMM observation of the moderately distant (z=0.41)galaxy cluster CL 0939+4713 (Abell 851), an exceptionally rich cluster. The formation and evolution of clusters depends sensitively
on cosmological parameters like the mean matter density in the universe Οm. Therefore it is important to determine the dynamical state of clusters at different redshifts, i.e. at different evolutionary
states. The X-ray morphology alone is not the best indicator of the dynamical state, but it should be complemented with all
other information available, e.g. the temperature map or the galaxy distribution. The combination of all findings gives a
detailed picture of the state of a cluster. This analysis, of this relatively distant cluster, can be used as a basis for
comparisons at lower and higher redshifts. The capability of XMM to perform spatially resolved spectroscopy can be used also
to determine the distribution of the metal abundances. Not only the overall value of metallicity but also its spatial distribution
gives important indications on the metal enrichment processes. The X-ray image shows pronounced substructure. There are two
main subclusters which have also some internal structure. This is an indication that the cluster is a dynamically young system.
This conclusion is supported by the temperature distribution: a hot region is found between the two main subclusters indicating
that the cluster is in the process of a major merger, in which the two subclusters will probably collide in a few hundreds
of Myr. The intra-cluster gas of CL 0939+4713 shows variations of the metal abundances. The optically richer subcluster has
a somewhat higher metallicity. This finding together with the absence of post-starburst galaxies in this region gives interesting
hints on the metal enrichment processes favouring recent enrichment processes like ram-pressure stripping or tidal stripping.
Throughout this paper we use H
0
=50 km s-1Mpc-1 and q
0
=0.5; all errors are 90% confidence levels.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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| Keywords: | Galaxies: clusters: general intergalactic medium evolution Cosmology: observations Cosmology: theory X-rays: galaxies: clusters |
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