Metal Abundances in the Hot Interstellar Medium in Early-Type Galaxies Observed with ASCA

TL;DR

This study analyzes ASCA X-ray data of 27 early-type galaxies to determine their interstellar medium metal abundances, revealing that Fe and alpha-element abundances are around solar levels in X-ray luminous galaxies, suggesting significant SN Ia product escape.

Contribution

First detailed analysis of metal abundances in early-type galaxies' hot ISM considering atomic physics uncertainties, showing Fe and alpha-element abundances are near solar in luminous galaxies.

Findings

Fe and alpha-element abundances are ~1 solar in X-ray luminous galaxies.

Uncertainties in atomic physics affect abundance measurements but can be mitigated.

X-ray faint galaxies have lower contributions from Type-Ia supernovae to their ISM.

Abstract

We have analyzed ASCA data of 27 early-type galaxies, and studied the properties of their X-ray emitting ISM (Inter Stellar Medium) in detail. We found that overlapping lines and free-bound continuum cause strong coupling in the derived abundances of various elements. The abundance determination is also difficult due to the uncertainties in the Fe-L atomic physics, because Fe-L lines couple with O and Ne K-lines. However, when abundances of $\alpha$-elements are fixed, all the plasma codes give similar Fe abundances with a scattering of only 20-30%. To relax the strong coupling among the elements, we included 20% systematic errors in the Fe-L region of the spectra. Then, in X-ray luminous galaxies, the derived abundance of Fe and $\alpha$-elements both became $\sim 1$ solar within a factor of 2. This result relaxes the previous severe discrepancy between the ISM and stellar metallicities. The ISM metallicity in X-ray fainter galaxies is still uncertain, but we can at least constrain that contribution from type-Ia SN to the ISM abundance is lower than in X-ray luminous systems. These results strongly suggest that a large fraction of SN Ia products have escaped into intergalactic space.