Chemical abundances in the outskirts of nearby galaxy groups measured with joint Suzaku and Chandra observations

Abstract

We report results from deep Suzaku and mostly snapshot Chandra observations of four nearby galaxy groups: MKW4, Antlia, RXJ1159+5531, and ESO3060170. Their peak temperatures vary over 2–3 keV, making them the smallest systems with gas properties constrained to their viral radii. The average Fe abundance in the outskirts (R > 0.25R200) of their intragroup medium (IGrM) is ZFe = 0.309 ± 0.018 Z⊙ with χ2 = 14 for 12 degrees of freedom, which is remarkably uniform and strikingly similar to that of massive galaxy clusters, and is fully consistent with the numerical predictions from the IllustrisTNG cosmological simulation. Our results support an early-enrichment scenario among galactic systems over an order of magnitude in mass, even before their formation. When integrated out to R200, we start to see a tension between the measured Fe content in ICM and what is expected from supernovae yields. We further constrain their O, Mg, Si, S, and Ni abundances. The abundance ratios of those elements relative to Fe are consistent with the predictions (if available) from IllustrisTNG. Their Type Ia supernovae fraction varies between 14 per cent–21 per cent. A pure core collapsed supernovae enrichment at group outskirts can be ruled out. Their cumulative iron-mass-to-light ratios within R200 are half that of the Perseus cluster, which may imply that galaxy groups do not retain all of their enriched gas due to their shallower gravitational potential wells, or that groups and clusters may have different star formation histories.

The composition and thermal properties of a cool core lacking a brightest cluster galaxy

“…The 𝛼/Fe ratios are found to be consistent with Solar abundances at their centers, but increase outside the cluster centers and reach 2× the Solar value. Interestingly, this latter measurement, with 𝛼/Fe profiles increasing with radius, is fully consistent with the prediction of the IllustrisTNG cosmological simulation (Sarkar et al 2022).…”

“…The abundance ratios outside cluster cores have been observed with Suzaku for only a few clusters (Sarkar et al 2022;Simionescu et al 2015). However, unlike cluster centers, agreement on abundance ratios of cluster outskirts has not been reached.…”

“…Abundance ratios of Si/Fe, Mg/Fe, and S/Fe out to its virial radius have been reported, which are generally consistent with the Solar value. Recently, Sarkar et al (2022) presented the O/Fe, Si/Fe, Mg/Fe, and S/Fe ratios for 4 low mass clusters out to their virial radii. The 𝛼/Fe ratios are found to be consistent with Solar abundances at their centers, but increase outside the cluster centers and reach 2× the Solar value.…”

“…However, the uncertainty of these measurements is greater than 20% and the measurements were performed with a spatial resolution of a few hundred kpc, therefore a non-uniform composition cannot be ruled out. Furthermore, the observed Fe mass in the ICM, when integrated to large radii, far exceeds what can be produced by the visible stellar population (Sarkar et al 2022;Ghizzardi et al 2021; E Black-★ E-mail:ysu262@g.uky.edu well et al 2021), which is difficult to reconcile with the prevailing enrichment model.…”

New Resonance Scattering Model in AtomDB: Application to Line Suppression in Galaxy Clusters and Elliptical Galaxies

“…Over the years, several studies reported the detection of the RS effect and demonstrated the importance of incorporating resonance scattering in modeling the X-ray spectra (Gilfanov et al 1987;Shigeyama 1998;Churazov et al 2004;Sanders & Fabian 2006;Nelson et al 2023). RS is crucial for the accurate determination of the abundances of heavy elements in the intracluster medium (Akimoto et al 2000;Sarkar et al 2022a), measurements of velocity fields and anisotropy of gas motion (Churazov et al 2010;Sarkar et al 2022bSarkar et al , 2023, and the polarization of bright X-ray emission lines in galaxy clusters and elliptical galaxies (Zhuravleva et al 2010). RS can be important for diagnostics of the density or ionization state using He-like ions, Fe L-shell ions, or the ratios of He-like to H-like ions (Schmelz et al 1992).…”