XMM observation of M~87 II. Abundance structure of the interstellar and intergalactic medium

TL;DR

This study analyzes the temperature and element abundance profiles of the intracluster medium in M~87 using XMM data, revealing gradients and ratios that inform on supernova contributions and chemical enrichment.

Contribution

It provides detailed radial abundance profiles of seven elements in M~87's ICM, highlighting the role of supernova types in chemical enrichment and the spatial distribution of elements.

Findings

Abundance of Si, S, Ar, Ca, and Fe decreases with radius, becoming nearly constant at ~1.5 solar.

Fe/Si ratio is approximately 0.9 solar with no radial gradient.

O abundance is lower at the center and has a flatter gradient.

Abstract

Based on a detailed study of the temperature structure of the intracluster medium in the halo of M~87, abundance profiles of 7 elements, O, Mg, Si, S, Ar, Ca, and Fe are derived. In addition, abundance ratios are derived from the ratios of line strengths, whose temperature dependences are small within the temperature range of the ICM of M~87. The abundances of Si, S, Ar, Ca and Fe show strong decreasing gradients outside 2$'$ and become nearly constant within the radius at $\sim1.5$ solar. The Fe/Si ratio is determined to be 0.9 solar with no radial gradient. In contrast, the O abundance is less than a half of the Si abundance at the center and has a flatter gradient. The Mg abundance is $\sim$1 solar within 2$'$, which is close to stellar abundance within the same radius. The O/Si/Fe pattern of M~87 is located at the simple extension of that of Galactic stars. The observed Mg/O ratio is about 1.25 solar, which is also the same ratio as for Galactic stars. The O/Si/Fe ratio indicates that the SN Ia contribution to Si and Fe becomes important towards the center and SN Ia products have similar abundances of Si and Fe at least around M~87, which may reflect dimmer SN Ia observed in old stellar systems. The S abundance is similar to the Si abundance at the center, but has a steeper gradient. This result suggests that the S/Si ratio of SN II products is much smaller than the solar ratio.