Interpretation of Abundance Ratios

Abstract

Abstract:In this paper we discuss abundance ratios and their relation to stellar nucleosynthesis and other parameters of chemical evolution models, reviewing and clarifying the correct use of the observed abundance ratios in several astrophysical contexts. In particular, we start from the well-known fact that abundance ratios depend on stellar yields, initial mass function, and stellar lifetimes, and we show, by means of specific examples, that in some cases it is not correct to infer constraints on the contributions from different supernovae types (Ia, II), and particularly on different sets of yields, in the absence of a complete chemical evolution model taking into account stellar lifetimes. In spite of the fact that some of these results should be well known, we believe that it is useful to discuss the meaning of abundance ratios in the light of several recent claims based upon an incorrect interpretation of observed abundance ratios. In particular, the procedure, often used in the recent literature, of directly deriving conclusions about stellar nucleosynthesis just by relating abundance ratios to yield ratios implicitly assumes the instantaneous recycling approximation. This approximation is clearly not correct when one analyses the contributions of supernovae type Ia relative to supernovae type II as functions of cosmic time. In this paper we show that the uncertainty which arises from adopting this oversimplified procedure in a variety of astrophysical objects, such as elliptical galaxies, the intracluster medium, and high redshift objects, does not allow us to draw any firm conclusion, and that the differences between abundance ratios predicted by models with the instantaneous recycling approximation and models with detailed stellar lifetimes is of the same order as the differences between different sets of yields. On the other hand, if one is interested only in establishing the global metal production (e.g. galaxies plus intracluster medium) over the lifetime of the Universe, then the adoption of simplified arguments can be justified.

Abundance ratios in the hot ISM of elliptical galaxies

“…The yields for each given element, as well as the recycling by low-mass single stars do play a role in shaping the abundance pattern. Matteucci & Chiappini (2005), Loewenstein & Davis (2010) stressed that to reproduce the abundance ratios of many elements it is important to ensure that an α-enhanced gas is ejected (recycled) by single low-mass stars. That is, the abundance ratios cannot be interpreted by comparing them directly to the predicted SNIa/SNII yield ratio pattern.…”

Metal abundances in the cool cores of galaxy clusters

“…the fraction of the iron mass synthesized in type Ia supernovae, M Fe,SNIa and M Fe,SNcc are respectively the total Fe mass ejected by SNIa and SNcc. Matteucci & Chiappini (2005) caution against an inappropriate use of Eq. (1) as in principle this equation is valid only if one is interested in the global Fe production (i.e., Fe in stars, galaxies and the ICM).…”

Chemical Evolution in Sersic 159-03 Observed with Xmm-Newton

“…A small part of the supernova products can also be locked up in low-mass stars, so the abundance distribution we observe in the ICM is not entirely representative for the total abundance distribution in the cluster. A more detailed description of the problems when one uses this simplified model is described in Matteucci & Chiappini (2005). The derived supernova ratios should be interpreted as the number fraction of supernovae that would be needed to enrich the ICM, not the actual number of supernovae during the history of the cluster.…”