EDP Sciences
Free Access
Volume 462, Number 2, February I 2007
Page(s) 429 - 442
Section Cosmology (including clusters of galaxies)
DOI https://doi.org/10.1051/0004-6361:20065568
Published online 02 November 2006

A&A 462, 429-442 (2007)
DOI: 10.1051/0004-6361:20065568

Tracing the evolution in the iron content of the intra-cluster medium

I. Balestra1, P. Tozzi2, 3, S. Ettori4, P. Rosati5, S. Borgani3, 6, V. Mainieri C. Norman1, 7, and M. Viola6

1  Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
    e-mail: balestra@mpe.mpg.de
2  INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
3  INFN, National Institute for Nuclear Physics, Trieste, Italy
4  INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
5  European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
6  Dipartimento di Astronomia dell'Università di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
7  Department of Physics and Astronomy, Johns Hopkins University, MD 21218 Baltimore, USA

(Received 8 May 2006/ Accepted 20 September 2006 )

Context.We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies at $z \ga 0.3$, which cover a temperature range of $3 \la {\it kT} \la 15$ keV.
Aims.Our analysis is aimed at measuring the iron abundance in the intra-cluster medium (ICM) out to the highest redshift probed to date.
Methods.We made use of combined spectral analysis performed over five redshift bins at $0.3\la z \la 1.3$ to estimate the average emission weighted iron abundance. We applied non-parametric statistics to assess correlations between temperature, metallicity, and redshift.
Results.We find that the emission-weighted iron abundance measured within $(0.15{-}0.3)\,R_{\rm vir}$ in clusters below 5 keV is, on average, a factor of ~2 higher than in hotter clusters, following $Z(T)\simeq 0.88\,T^{-0.47}~Z_\odot$, which confirms the trend seen in local samples. We also find a constant average iron abundance $Z_{\rm Fe}\simeq 0.25~Z_\odot$ as a function of redshift, but only for clusters at $z\ga0.5$. The emission-weighted iron abundance is significantly higher ( $Z_{\rm Fe}\simeq0.4~Z_\odot$) in the redshift range $z\simeq0.3{-}0.5$, approaching the value measured locally in the inner $0.15~R_{\rm vir}$ radii for a mix of cool-core and non cool-core clusters in the redshift range 0.1<z<0.3. The decrease in metallicity with redshift can be parametrized by a power law of the form ~ (1+z)-1.25. We tested our results against selection effects and the possible evolution in the occurrence of metallicity and temperature gradients in our sample, and we do not find any evidence of a significant bias associated to these effects.
Conclusions.The observed evolution implies that the average iron content of the ICM at the present epoch is a factor of ~2 larger than at $z\simeq 1.2$. We confirm that the ICM is already significantly enriched ( $Z_{\rm Fe}\simeq 0.25~Z_\odot$) at a look-back time of 9 Gyr. Our data provide significant constraints on the time scales and physical processes that drive the chemical enrichment of the ICM.

Key words: cosmology: observations -- X-rays: galaxies: clusters

© ESO 2007

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