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

• Published in: Astronomy and astrophysics (Berlin) 2007-02, Vol.462 (2), p.429-442
• Main Authors: Balestra, I., Tozzi, P., Ettori, S., Rosati, P., Borgani, S., Norman, V. Mainieri C., Viola, M.
• Format: Article
• Language: English
• Subjects: Astronomy; cosmology: observations; Earth, ocean, space; Exact sciences and technology; X-rays: galaxies: clusters
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20065568

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