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Date and Time of the Query: 2019-05-22 T23:27:55 PDT
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For refcode 2007A&A...462..429B:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2007A&A...462..429B Tracing the evolution in the iron content of the intra-cluster medium Balestra, I.; Tozzi, P.; Ettori, S.; Rosati, P.; Borgani, S.; Norman, V. Mainieri C.; Viola, M. Abstract. Context: We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies at z >~ 0.3, which cover a temperature range of 3 <~ {kT} <~ 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<~ z <~ 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_vir in clusters below 5 keV is, on average, a factor of 2 higher than in hotter clusters, following Z(T)~= 0.88 T^-0.47^ Z_o, which confirms the trend seen in local samples. We also find a constant average iron abundance Z_Fe~= 0.25 Z_o as a function of redshift, but only for clusters at z >~ 0.5. The emission-weighted iron abundance is significantly higher (Z_Fe~=0.4 Z_o) in the redshift range z~=0.3-0.5, approaching the value measured locally in the inner 0.15 R_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~= 1.2. We confirm that the ICM is already significantly enriched (Z_Fe~=0.25 Z_o) 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
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