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

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 ~ 1.5 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 ~ 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.