Research Note

The evolution of the spatially resolved metal abundance in galaxy clusters up to z = 1.4^⋆

¹ INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna Italy
e-mail: stefano.ettori@oabo.inaf.it
² INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
³ Physics and Astronomy Dept., Michigan State University, East Lansing, MI 48824, USA
⁴ INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
⁵ INAF–IASF, via Bassini 15, 20133 Milan, Italy
⁶ Department of Physics and Astronomy, University of California at Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697–4575, USA
⁷ INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy

Received: 5 December 2014
Accepted: 1 April 2015

Abstract

Context. We present the combined analysis of the metal content of 83 objects in the redshift range 0.09−1.39, and spatially resolved in the three bins (0−0.15, 0.15−0.4, >0.4) R₅₀₀, as obtained with similar analysis using XMM-Newton data in our previous two papers.

Aims. By combining these two large data sets, we investigate the relations between abundance, temperature, radial position and redshift holding in the intracluster medium.

Methods. We fit functional forms to the combination of the different physical quantities of interest, i.e., intracluster medium (ICM) metal abundance, radius, and redshift. We use the pseudo-entropy ratio to separate the cool core (CC) cluster population, where the central gas density tends to be relatively higher, cooler and more metal rich, from the non-cool core systems.

Results. The average, redshift-independent, metal abundance measured in the three radial bins decreases moving outwards, with a mean metallicity in the core that is even three (two) times higher than the value of 0.16 times the solar abundance in Anders & Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197) estimated at r> 0.4 R₅₀₀ in CC (NCC) objects. We find that the values of the emission-weighted metallicity are well fitted by the relation Z(z) = Z₀ (1 + z)^{− γ} at the given radius. A significant scatter, intrinsic to the observed distribution and of the order of 0.05−0.15, is observed below 0.4 R₅₀₀. The nominal best-fit value of γ is significantly different from zero (>3σ) in the inner cluster regions (γ = 1.6 ± 0.2) and in CC clusters only. These results are also confirmed with a bootstrap analysis, which provides a still significant negative evolution in the core of CC systems (P> 99.9 per cent, when counting the number of random repetitions, which yields γ> 0). No redshift evolution is observed when regions above the core (r> 0.15 R₅₀₀) are considered. A reasonable good fit of both the radial and redshift dependence is provided from the functional form Z(r,z) = Z₀(1 + (r/ 0.15 R₅₀₀)²)^{− β}(1 + z)^{− γ}, with (Z₀,β,γ) = (0.83 ± 0.13,0.55 ± 0.07,1.7 ± 0.6) in CC clusters and (0.39 ± 0.04,0.37 ± 0.15,0.5 ± 0.5) for NCC systems.

Conclusions. Our results represent the most extensive study of the spatially resolved metal distribution in the cluster plasma as function of redshift. Our study defines the limits that numerical and analytic models describing the metal enrichment in the ICM have to meet.