CHEERS: The chemical evolution RGS sample

Abstract

Context. The chemical yields of supernovae and the metal enrichment of the intra-cluster medium (ICM) are not well understood. The hot gas in clusters of galaxies has been enriched with metals originating from billions of supernovae and provides a fair sample of large-scale metal enrichment in the Universe. High-resolution X-ray spectra of clusters of galaxies provide a unique way of measuring abundances in the hot intracluster medium (ICM). The abundance measurements can provide constraints on the supernova explosion mechanism and the initial-mass function of the stellar population. This paper introduces the CHEmical Enrichment RGS Sample (CHEERS), which is a sample of 44 bright local giant ellipticals, groups, and clusters of galaxies observed with XMM-Newton. Aims. The CHEERS project aims to provide the most accurate set of cluster abundances measured in X-rays using this sample. This paper focuses specifically on the abundance measurements of O and Fe using the reflection grating spectrometer (RGS) on board XMM-Newton. We aim to thoroughly discuss the cluster to cluster abundance variations and the robustness of the measurements. Methods. We have selected the CHEERS sample such that the oxygen abundance in each cluster is detected at a level of at least 5σ in the RGS. The dispersive nature of the RGS limits the sample to clusters with sharp surface brightness peaks. The deep exposures and the size of the sample allow us to quantify the intrinsic scatter and the systematic uncertainties in the abundances using spectral modeling techniques. Results. We report the oxygen and iron abundances as measured with RGS in the core regions of all 44 clusters in the sample. We do not find a significant trend of O/Fe as a function of cluster temperature, but we do find an intrinsic scatter in the O and Fe abundances from cluster to cluster. The level of systematic uncertainties in the O/Fe ratio is estimated to be around 20−30%, while the systematic uncertainties in the absolute O and Fe abundances can be as high as 50% in extreme cases. Thanks to the high statistics of the observations, we were able to identify and correct a systematic bias in the oxygen abundance determination that was due to an inaccuracy in the spectral model. Conclusions. The lack of dependence of O/Fe on temperature suggests that the enrichment of the ICM does not depend on cluster mass and that most of the enrichment likely took place before the ICM was formed. We find that the observed scatter in the O/Fe ratio is due to a combination of intrinsic scatter in the source and systematic uncertainties in the spectral fitting, which we are unable to separate. The astrophysical source of intrinsic scatter could be due to differences in active galactic nucleus activity and ongoing star formation in the brightest cluster galaxy. The systematic scatter is due to uncertainties in the spatial line broadening, absorption column, multi-temperature structure, and the thermal plasma models.

L-GALAXIES 2020: Spatially resolved cold gas phases, star formation, and chemical enrichment in galactic discs

“…Here, we further refine this technique by including two modifications. First, we update the Z Fe radial profile assumed when re-scaling all measurements to that presented by Mernier et al (2017), which is based on a set of 44 groups and clusters from the CHEERS sample (de Plaa et al 2017) observed with XMM-Newton. This CHEERS analysis found very similar profile shapes for groups and clusters.…”

Searching for cool and cooling X-ray emitting gas in 45 galaxy clusters and groups

“…The CHEERS project includes clusters, groups and elliptical galaxies with the O VIII line detected at 5 σ in the Reflection Grating Spectrometer (RGS) spectra (Pinto et al 2015), and provides a moderately large sample of objects with deep exposure times. Some of the original aims of the CHEERS project were to accurately measure the abundances of key elements, e.g, O and Fe (de Plaa et al 2017) and constrain the level of turbulence (Pinto et al 2015). These suggest that the sample is also suitable for measuring the cooling structure of clusters below 1-2 keV, since the relevant O and Fe ionisation stages in the soft X-ray band are strong and usually peak at different temperatures.…”

Lessons learned from 19 years of high‐resolution X‐ray spectroscopy of galaxy clusters with the reflection grating spectrometer on board XMM‐Newton

“…On average, the relative fractions of type Ia supernovae are SN Ia/(SN Ia + SN cc) ∼25–45%, possibly larger than the Solar environment (∼15–25%) and, therefore, suggest additional production of heavy elements from recent SN type Ia in the BCG. However, the uniformity of the O/Fe and Ne/Fe abundance ratios over more than an order of magnitude in mass range (from giant ellipticals to groups and then clusters of galaxies) and the lack of spatial gradients and distribution with the redshift indicate that either most metals were formed around z ∼2 or that several phenomena such as sloshing and metal uplift by AGN bubbles redistributed the metals (de Plaa et al ; Mernier et al ).…”

“…RGS has been crucial in testing the accuracy of atomic databases for plasmas at ∼ 0.1–1 keV temperatures. de Plaa et al () and Gu et al () have shown that RGS spectra are sensitive enough to distinguish among different calculations of atomic cross‐sections. The ICM abundance pattern seems to agree with that of the Sun if state‐of‐art atomic databases are adopted (Section 4.2 and Gu et al ).…”