Mass-invariance of the iron enrichment in the hot haloes of massive ellipticals, groups, and clusters of galaxies

Abstract

X-ray measurements find systematically lower Fe abundances in the X-ray emitting haloes pervading groups (kT 1.7 keV) than in clusters of galaxies. These results have been difficult to reconcile with theoretical predictions. However, models using incomplete atomic data or the assumption of isothermal plasmas may have biased the best fit Fe abundance in groups and giant elliptical galaxies low. In this work, we take advantage of a major update of the atomic code in the spectral fitting package spex to re-evaluate the Fe abundance in 43 clusters, groups, and elliptical galaxies (the CHEERS sample) in a self-consistent analysis and within a common radius of 0.1r 500 . For the first time, we report a remarkably similar average Fe enrichment in all these systems. Unlike previous results, this strongly suggests that metals are synthesised and transported in these haloes with the same average efficiency across two orders of magnitude in total mass. We show that the previous metallicity measurements in low temperature systems were biased low due to incomplete atomic data in the spectral fitting codes. The reasons for such a code-related Fe bias, also implying previously unconsidered biases in the emission measure and temperature structure, are discussed.

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

“…15 shows model results for the relation between the temperature of the hot ICM at r 500 , T 500 (a proxy for the gravitating mass), and the mean iron abundance within r 500 (the black points). Also shown are the observational dataset from Yates et al (2017) for clusters (orange points), and from Mernier et al (2018b) for clusters and groups (light blue points).…”

“…The same procedure is also applied to our model systems, which are assumed to have a Mernier et al (2017) profile when re-scaling the iron abundance from within r 200 to within r 500 (see Section 5 of Yates et al 2017 for details. ) Second, we take account of recent improvements to the way iron abundances are obtained from the X-ray spectra of galaxy groups (Mernier et al 2018b) by excluding from our comparison the observational data for galaxy groups compiled by Yates et al (2017) that relied on Z Fe estimates obtained from older spectral-fitting codes. For clusters, Mernier et al (2018b) found little difference in the Z Fe estimates obtained from older and newer versions of SPEX-ACT.…”

“…) Second, we take account of recent improvements to the way iron abundances are obtained from the X-ray spectra of galaxy groups (Mernier et al 2018b) by excluding from our comparison the observational data for galaxy groups compiled by Yates et al (2017) that relied on Z Fe estimates obtained from older spectral-fitting codes. For clusters, Mernier et al (2018b) found little difference in the Z Fe estimates obtained from older and newer versions of SPEX-ACT. Therefore, we choose to include both the CHEERS dataset and that of Yates et al (2017) in this highertemperature regime.…”

How do atomic code uncertainties affect abundance measurements in the intracluster medium?

“…Another (yet no less important) source of systematic uncertainties concerns our current knowledge of the atomic processes that produce the continuum and the emission lines in ICM spectra. For instance, it has been shown that improvements in atomic codes can significantly affect measurements of absolute Fe abundances in groups and ellipticals (Mernier et al ) and of X/Fe abundance ratios in more massive systems (Mernier et al ), thereby altering their astrophysical interpretations. Nowadays, most of the ICM abundances reported in the literature rely on two sets of atomic codes/tables (Table ).…”

Iron abundance distribution in the hot gas of merging galaxy clusters

“…Uncertainties regarding the atomic codes are limited by the fact that we are using the update of the code SPEXACT and SPEX, which incorporate more precise modelling of the atomic processes and extensive compilation of transitions. However, uncertainties due to a not complete atomic database are still present (Hitomi Collaboration et al 2018) and their effects can be nonnegligible (Mernier et al 2018a).…”