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

TL;DR

This study re-evaluates iron abundance in hot haloes of various cosmic systems using updated atomic data, revealing a universal enrichment level across different masses, challenging previous lower measurements in smaller systems.

Contribution

It provides the first consistent analysis showing similar iron enrichment in groups, ellipticals, and clusters, correcting biases from outdated atomic data.

Findings

Iron enrichment is similar across all studied systems.

Previous low measurements were due to atomic data biases.

Metal synthesis and transport are equally efficient across systems.

Abstract

X-ray measurements find systematically lower Fe abundances in the X-ray emitting haloes pervading groups ($kT\lesssim1.7$ 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 0.1$r_{500}$. 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.