Accurate Determination of Chemical Abundances near a Supermassive Black Hole

TL;DR

This study uses high-resolution X-ray spectroscopy to analyze metal abundances near a supermassive black hole, revealing recent supernova enrichment patterns in the galactic nucleus.

Contribution

It presents new observations of the Circinus Galaxy's nucleus with XRISM, providing detailed metal abundance patterns and insights into supernova contributions near a black hole.

Findings

Material responsible for iron-Kα emission is cold, metal-rich, and located >0.024 pc from the black hole.

Abundance pattern indicates dominance of core-collapse supernovae from stars less than 20 M_.

Gas feeding the black hole was enriched by recent core-collapse supernovae.

Abstract

The metal abundances in galactic nuclei carry key information on the history of star formation and mass transfer in central regions of galaxies. X-ray fluorescence analysis is a unique tool to reliably measure the abundances of various elements via simple physics. Here we present a new observation of the active nucleus in the Circinus Galaxy with the XRISM satellite at unprecedented X-ray energy resolution. The fluorescent iron-K$\alpha$ line profile modified by Compton scattering indicates that the material responsible for its emission is cold, metal-rich, and is located $\gtrsim$0.024 parsecs (pc) from the supermassive black hole, consistent with the dusty torus region. The abundance pattern derived from comparing fluorescent line intensities of different metals shows sub-solar ratios of argon- and calcium-to-iron, and a super-solar ratio of nickel-to-iron. This abundance pattern is best produced by a combination in number fraction of $92^{+2}_{-4}$\% core-collapse supernovae from progenitor stars less massive than $20^{+3}_{-2} M_\odot$ and $8^{+4}_{-2}$\% type-Ia SNe. This suggests that gas feeding the super-massive black hole was enriched by recent core-collapse supernovae. Our findings imply that in metal-rich environments stars more massive than about 20 $M_\odot$ directly collapse into black holes or make faint SNe without ejecting heavy metals into the space.