Origin of central abundances in the hot intra-cluster medium

Abstract

The hot intra-cluster medium (ICM) is rich in metals, which are synthesised by supernovae (SNe) explosions and accumulate over time into the deep gravitational potential well of clusters of galaxies. Since most of the elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse (SNcc) supernovae, measuring their abundances gives us direct information on the nucleosynthesis products of billions of SNe since the epoch of the star formation peak (z ∼ 2−3). In this study, we use the EPIC and RGS instruments on board XMM-Newton to measure the abundances of nine elements (O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni) from a sample of 44 nearby cool-core galaxy clusters, groups, and elliptical galaxies. We find that the Fe abundance shows a large scatter (∼20−40%) over the sample, within 0.2r 500 and especially 0.05r 500 . Unlike the absolute Fe abundance, the abundance ratios (X/Fe) are uniform over the considered temperature range (∼0.6−8 keV) and with a limited scatter. In addition to an unprecedented treatment of systematic uncertainties, we provide the most accurate abundance ratios measured so far in the ICM, including Cr/Fe and Mn/Fe which we firmly detected (>4σ with MOS and pn independently). We find that Cr/Fe, Mn/Fe, and Ni/Fe differ significantly from the proto-solar values. However, the large uncertainties in the proto-solar abundances prevent us from making a robust comparison between the local and the intra-cluster chemical enrichments. We also note that, interestingly, and despite the large net exposure time (∼4.5 Ms) of our dataset, no line emission feature is seen around ∼3.5 keV.

Radial metal abundance profiles in the intra-cluster medium of cool-core galaxy clusters, groups, and ellipticals

“…All the observations considered here are taken from the CHEERS 2 catalogue (de Plaa et al 2017;Mernier et al 2016a). This sample, optimised to study chemical enrichment in the ICM, consists of 44 nearby cool-core galaxy clusters, groups, and ellipticals for which the O viii 1s-2p line at ∼19 Å is detected with >5σ in their XMM-Newton/RGS spectra.…”

“…where N H i and N H,tot are the atomic and total (atomic and molecular) hydrogen column densities, respectively (for further details, see Mernier et al 2016a). …”

“…As discussed extensively in Mernier et al (2015) and Mernier et al (2016a), the abundances measured from a fit covering the full EPIC energy band may be significantly biased, especially for deep exposure datasets. In fact, a slightly incorrect calibration in the effective area may result in an incorrect prediction of the local continuum close to an emission line.…”

“…Therefore, in the rest of the analysis, we measure the O, Mg, Si, S, Ca, Ar, and Ni abundances by fitting the EPIC spectra within several narrow energy ranges centred around their K-shell emission lines (hereafter the "local" fits; Mernier et al 2016a). The temperature parameters (kT mean and σ T ) are fixed to their values derived from initial fits performed within the broad energy band (hereafter the "global" fits).…”

“…With excellent Suzaku and XMM-Newton exposures, the abundance of other elements, such as carbon, nitrogen (e.g. Werner et al 2006a;Sanders & Fabian 2011, Mao et al 2017, to be submitted), or even chromium and manganese (Tamura et al 2009;Mernier et al 2016a), could be reasonably constrained as well.…”