Further evidence for a merger in Abell 2218 from an XMM-Newton observation

Free access article

Issue		A&A Volume 433, Number 3, April III 2005


Page(s)		777 - 785
Section		Cosmology (including clusters of galaxies)
DOI		http://dx.doi.org/10.1051/0004-6361:20041415

A&A 433, 777-785 (2005)
DOI: 10.1051/0004-6361:20041415

Further evidence for a merger in Abell 2218 from an XMM-Newton observation

G. W. Pratt, H. Böhringer and A. Finoguenov

MPE Garching, Giessenbachstraße, 85748 Garching, Germany
e-mail: gwp@mpe.mpg.de

(Received 4 June 2004 / Accepted 17 December 2004)

Abstract
The galaxy cluster Abell 2218, at z=0.171, is well-known for the discrepancy between mass estimates derived from X-ray and strong lensing analyses. With the present XMM-Newton observation, we are able to trace the gas density and temperature profiles out to a radius of ${\sim} 1400~h_{70}^{-1}$ kpc (approximately the virial radius of the cluster). The overall surface brightness profile is well fitted over three orders of magnitude with a simple $\beta$ -model with a core radius of $0\farcm95$ and $\beta = 0.63$ . The projected temperature profile declines steeply with radius (by ${\sim} 50\%$ ), and is well described by a polytrope with parameters t₀ = 8.09 keV and $\gamma=1.15$ . The temperature map shows a pronounced peak in the central arcminute, where the temperature rises by a factor of two (from ${\sim} 5$ to ${\sim} 10$ keV). The mass profile, calculated assuming hydrostatic equilibrium and spherical symmetry, is best fitted with a King approximation to an isothermal sphere, implying a dark matter distribution with a central core, in contrast with the cusped cores found in more obviously relaxed clusters. The X-ray mass is approximately two times less than the strong lensing mass at $r \sim 80~h_{50}^{-1}$ kpc, although the agreement between X-ray and weak lensing mass measurements at larger radius ( $r \sim 400~h_{50}^{-1}$ kpc) is slightly better. While the X-ray total mass estimates can vary by 30 per cent depending on the mass model, all measurements are significantly lower than the corresponding total mass from optical measurements. Given the X-ray results indicating considerable disturbance of the intracluster gas, leading to a probable violation of the assumption of hydrostatic equilibrium, and the observed substructure in the optical, suggesting a line-of-sight merger, it is unlikely that the different mass estimates of this cluster can be reconciled, at least with standard modelling assumptions.

Key words: galaxies: clusters: individual: A2218 -- galaxies: intergalactic medium -- cosmology: observations -- cosmology: dark matter -- X-rays: galaxies: clusters

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.