X-ray measured metallicities of the intra-cluster medium: a good measure for the metal mass?

TL;DR

This study assesses how accurately X-ray observations trace the metal content in galaxy clusters' intra-cluster medium, revealing that metal distribution inhomogeneity leads to underestimates of total metal mass, though X-ray maps are reliable for spatial comparisons.

Contribution

It demonstrates the dependence of metallicity estimates on metal distribution and validates the use of X-ray weighted metal maps against synthetic spectra, highlighting limitations in measuring total metal mass.

Findings

X-ray metallicity maps closely match synthetic spectra maps above 30 million K.

Metal mass is often underestimated by up to a factor of three in cluster centers.

Inhomogeneous metal distribution reduces the accuracy of X-ray metallicity as a metal mass proxy.

Abstract

Aims. We investigate whether X-ray observations map heavy elements in the Intra-Cluster Medium (ICM) well and whether the X-ray observations yield good estimates for the metal mass, with respect to predictions on transport mech- anisms of heavy elements from galaxies into the ICM. We further test the accuracy of simulated metallicity maps. Methods. We extract synthetic X-ray spectra from N-body/hydrodynamic simulations including metal enrichment pro- cesses, which we then analyse with the same methods as are applied to observations. By changing the metal distribution in the simulated galaxy clusters, we investigate the dependence of the overall metallicity as a function of the metal distribution. In addition we investigate the difference of X-ray weighted metal maps produced by simulations and metal maps extracted from artifcial X-ray spectra, which we calculate with SPEX2.0 and analyse with XSPEC12.0. Results. The overall metallicity depends strongly on the distribution of metals within the galaxy cluster. The more inhomogeneously the metals are distributed within the cluster, the less accurate is the metallicity as a measure for the true metal mass. The true metal mass is generally underestimated by X-ray observations. The difference between the X-ray weighted metal maps and the metal maps from synthetic X-ray spectra is on average less than 7% in the temperature regime above T > 3E7 K, i.e. X-ray weighted metal maps can be well used for comparison with observed metal maps. Extracting the metal mass in the central parts (r < 500 kpc) of galaxy clusters with X-ray observations results in metal mass underestimates up to a factor of three.