Astronomy and Astrophysics, volume 462, 429-442 (2007/2-1)
Tracing the evolution in the iron content of the intra-cluster medium.
BALESTRA I., TOZZI P., ETTORI S., ROSATI P., BORGANI S., MAINIERI V., NORMAN C. and VIOLA M.
Abstract (from CDS):
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. Our analysis is aimed at measuring the iron abundance in the intra-cluster medium (ICM) out to the highest redshift probed to date. 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. We find that the emission-weighted iron abundance measured within (0.15-0.3)Rvir in clusters below 5 keV is, on average, a factor of ∼2 higher than in hotter clusters, following Z(T)≃0.88T–0.47Z☉, which confirms the trend seen in local samples. We also find a constant average iron abundance ZFe≃0.25Z☉ as a function of redshift, but only for clusters at z>0.5. The emission-weighted iron abundance is significantly higher (ZFe≃0.4Z☉) in the redshift range z≃0.3-0.5, approaching the value measured locally in the inner 0.15Rvir 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. 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 (ZFe≃0.25Z☉) at a look-back time of 9Gyr. Our data provide significant constraints on the time scales and physical processes that drive the chemical enrichment of the ICM.
cosmology: observations - X-rays: galaxies: clusters
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