XMM-Newton high-resolution spectroscopy reveals the chemical evolution of M 87

Abstract

We present a study of chemical abundances in the giant elliptical galaxy M 87 using high-resolution spectra obtained with the Reflection Grating Spectrometers during two deep XMM-Newton observations. While we confirm the two-temperature structure of the inter-stellar medium (ISM) in M 87, we also show that a continuous temperature distribution describes the data equally well. The high statistics allow us, for the first time, to also determine relatively accurate abundance values for carbon and nitrogen. The comparison of the abundance ratios of C, N, O, and Fe in the ISM of M 87 with those in the stellar population of our Galaxy shows that the relative contribution of core-collapse supernovae to the enrichment of the ISM in M 87 is significantly less than in the Milky Way and indicates that the enrichment of the ISM by iron through Type Ia supernovae and by carbon and nitrogen is occurring in parallel. This suggests that the main sources of carbon and nitrogen in M 87 are the low- and intermediate-mass asymptotic giant branch stars. From the oxygen to iron abundance ratio in the hot gas, we estimate that the relative number of core collapse and type Ia supernovae contributing to the enrichment of the ISM in the core of M 87 is ∼60% and ∼40% respectively. The spatial distributions of iron and oxygen are different. Although the oxygen abundance distribution is flat, the iron abundance peaks in the core and has a gradient throughout the 4' wide field of view of the instrument, suggesting early enrichment by core-collapse supernovae and a continuous contribution of type Ia supernovae.