Iron in X-COP: Tracing enrichment in cluster outskirts with high accuracy abundance profiles (Corrigendum)
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Cited by 3 publications
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In intermediate-mass galaxy clusters (M = 2 − 4 × 10 14 M ⊙ , or equivalently T = 2.5 − 4.5 keV), abundance measurements are almost equally driven by iron K and L transitions at ∼ 6.7 keV and 0.9 − 1.3 keV, respectively. While K-shell-derived measurements are considered reliable, the resolution of the currently available instrumentation, as well as our current knowledge of the atomic processes, makes the modelling of the L-line complex challenging, resulting in potential biases for abundance measurements. In this work we study with unprecedented accuracy the systematics related to the modelling of the Fe L-line complex that may influence iron-abundance measurements in the intermediate-mass range. To this end, we selected a sample of three bright and nearby galaxy clusters, with long XMM-Newton observations available and temperatures in the 2.5 − 4.5 keV range. We fit the spectra extracted from concentric rings with APEC and APEC+APEC models, by alternately excluding one band (L-shell or Kα) at a time, and derived the fractional difference of the metal abundances ∆Z/Z as an indication of the consistency between K-and L-shell-derived measurements. The ∆Z/Z distribution was then studied as a function of the cluster radius, ring temperature, and X-ray flux. The L-blend-induced systematics, measured through an individual fit of each XMM-Newton MOS and pn camera spectrum, remain constant at a 5 − 6% value in the whole 2.5 − 4.5 keV temperature range. Conversely, a joint fit of MOS and pn spectra leads to a slight excess of 1 − 2% in this estimate. No significant dependence on the ring X-ray flux is highlighted. The measured 5 − 8% value indicates a modest contribution of the systematics to the derived iron abundances, giving confidence for future measurements. To date, these findings represent the best achievable estimate of the systematics in analysis, while future microcalorimeters will significantly improve our understanding of the atomic processes underlying the Fe L emissions.
In intermediate-mass galaxy clusters (M = 2 − 4 × 10 14 M ⊙ , or equivalently T = 2.5 − 4.5 keV), abundance measurements are almost equally driven by iron K and L transitions at ∼ 6.7 keV and 0.9 − 1.3 keV, respectively. While K-shell-derived measurements are considered reliable, the resolution of the currently available instrumentation, as well as our current knowledge of the atomic processes, makes the modelling of the L-line complex challenging, resulting in potential biases for abundance measurements. In this work we study with unprecedented accuracy the systematics related to the modelling of the Fe L-line complex that may influence iron-abundance measurements in the intermediate-mass range. To this end, we selected a sample of three bright and nearby galaxy clusters, with long XMM-Newton observations available and temperatures in the 2.5 − 4.5 keV range. We fit the spectra extracted from concentric rings with APEC and APEC+APEC models, by alternately excluding one band (L-shell or Kα) at a time, and derived the fractional difference of the metal abundances ∆Z/Z as an indication of the consistency between K-and L-shell-derived measurements. The ∆Z/Z distribution was then studied as a function of the cluster radius, ring temperature, and X-ray flux. The L-blend-induced systematics, measured through an individual fit of each XMM-Newton MOS and pn camera spectrum, remain constant at a 5 − 6% value in the whole 2.5 − 4.5 keV temperature range. Conversely, a joint fit of MOS and pn spectra leads to a slight excess of 1 − 2% in this estimate. No significant dependence on the ring X-ray flux is highlighted. The measured 5 − 8% value indicates a modest contribution of the systematics to the derived iron abundances, giving confidence for future measurements. To date, these findings represent the best achievable estimate of the systematics in analysis, while future microcalorimeters will significantly improve our understanding of the atomic processes underlying the Fe L emissions.
Metal enrichment: The apex accretor perspective
The goal of this work is to devise a description of the enrichment process in large-scale structure that explains the available observations and makes predictions for future measurements. We took a spartan approach to this study, employing observational results and algebra to connect stellar assembly in star-forming halos with metal enrichment of the intra-cluster and group medium. On one hand, our construct is the first to provide an explanation for much of the phenomenology of metal enrichment in clusters and groups. It sheds light on the lack of redshift evolution in metal abundance, as well as the small scatter of metal abundance profiles, the entropy versus abundance anti-correlation found in cool core clusters, and the so-called Fe conundrum, along with several other aspects of cluster enrichment. On the other hand, it also allows us to infer the properties of other constituents of large-scale structure. We find that gas that is not bound to halos must have a metal abundance similar to that of the ICM and only about one-seventh to one-third of the Fe in the Universe is locked in stars. A comparable amount is found in gas in groups and clusters and, lastly and most importantly, about three-fifths of the total Fe is contained in a tenuous warm or hot gaseous medium in or between galaxies. We point out that several of our results follow from two critical but well motivated assumptions: 1) the stellar mass in massive halos is currently underestimated and 2) the adopted Fe yield is only marginally consistent with predictions from synthesis models and SN rates. One of the most appealing features of the work presented here is that it provides an observationally grounded construct where vital questions on chemical enrichment in the large-scale structure can be addressed. We hope that it may serve as a useful baseline for future works.
CIZA J1358.9−4750 is a nearby galaxy cluster in the early phase of a major merger. The two-dimensional temperature map using XMM-Newton EPIC-PN observation confirms the existence of a high-temperature region, which we call the “hot region,” in the “bridge region” connecting the two clusters. The ∼500 kpc wide region between the south-east and north-west boundaries also has higher pseudo-pressure compared to the unshocked regions, suggesting the existence of two shocks. The southern shock front is clearly visible in the X-ray surface brightness image and has already been reported by Kato et al. (2015, PASJ, 67, 71). The northern one, on the other hand, is newly discovered. To evaluate their Mach number, we constructed a three-dimensional toy merger model with overlapping shocked and unshocked components in the line of sight. The unshocked and pre-shock intracluster medium (ICM) conditions are estimated based on those outside the interacting bridge region, assuming point symmetry. The hot-region spectra are modeled with two-temperature thermal components, assuming that the shocked condition follows the Rankin–Hugoniot relation with the pre-shock condition. As a result, the shocked region is estimated to have a line-of-sight depth of ∼1 Mpc with a Mach number of ∼1.3 in the south-east shock and ∼1.7 in the north-west shock. The age of the shock waves is estimated to be ∼260 Myr. This three-dimensional merger model is consistent with the Sunyaev–Zel’dovich signal obtained using the Planck observation within the cosmic microwave background fluctuations. The total flow of the kinetic energy of the ICM through the south-east shock was estimated to be ∼2.2 × 1042 erg s−1. Assuming that $10\%$ of this energy is converted into ICM turbulence, the line–of–sight velocity dispersion is calculated to be ∼200 km s−1, which is basically resolvable via upcoming high spectral resolution observations.
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