[Paper Review] CHEMICAL ABUNDANCES IN CLUSTERS OF GALAXIES

F. Matteuccí, B. K. Gibson|arXiv (Cornell University)|Mar 14, 1995

Stellar, planetary, and galactic studies3 citations

TL;DR

This paper investigates the origin of iron and alpha-elements (O, Mg, Si) in the intracluster medium (ICM) of galaxy clusters using a detailed galactic evolution model with supernova-driven winds. It demonstrates that the initial mass function (IMF) critically determines [O/Fe] and Fe mass-to-luminosity ratios, with flatter IMFs (x ≈ 1) preferred to match ASCA data, showing ~70% of ICM iron originates from Type II supernovae and 30% from Type Ia events.

ABSTRACT

We study the origin of iron and alpha-elements (O, Mg, Si) in clusters of galaxies. In particular, we discuss the [O/Fe] ratio and the iron mass-to-luminosity ratio in the intracluster medium (ICM) and their link to the chemical and dynamical evolution of elliptical and lenticular galaxies. We adopt a detailed model of galactic evolution incorporating the development of supernovae- driven galactic winds which pollute the ICM with enriched ejecta. We demonstrate \it quantitatively m the crucial dependence upon the assumed stellar initial mass function in determining the evolution of the mass and abundances ratios of heavy elements in typical model ICMs. We show that completely opposite behaviours of [alpha/Fe] ratios (\ie positive versus negative ratios) can be obtained by varying the initial mass function without altering the classic assumptions regarding type Ia supernovae progenitors or their nucleosynthesis. Our results indicate that models incorporating somewhat flatter-than-Salpeter initial mass functions (ie x approx 1, as opposed to x=1.35) are preferred, provided the intracluster medium iron mass-to-luminosity ratio, preliminary [alpha/Fe]>0 ASCA results, and present-day type Ia supernovae rates, are to be matched. A simple Virgo cluster simulation which adheres to these constraints shows that approx 70% of the measured ICM iron mass has its origin in type II supernovae, with the remainder being synthesized in type Ia systems.

Motivation & Objective

• To understand the origin of iron and alpha-elements (O, Mg, Si) in the intracluster medium (ICM) of galaxy clusters.
• To investigate how the initial mass function (IMF) influences the evolution of heavy-element abundances and mass-to-luminosity ratios in the ICM.
• To reconcile observed [O/Fe] ratios and iron mass-to-luminosity ratios with theoretical models of galactic chemical evolution.
• To determine the relative contributions of Type II and Type Ia supernovae to the ICM iron budget.

Proposed method

• A detailed model of galactic chemical evolution is employed, incorporating supernova-driven galactic winds that eject enriched material into the ICM.
• The model tracks the production and ejection of alpha-elements and iron from both Type II and Type Ia supernovae across different stellar populations.
• The initial mass function (IMF) is varied parametrically (from Salpeter-like x=1.35 to flatter x≈1) to assess its impact on ICM abundance ratios.
• The model is calibrated against observational constraints: the present-day Type Ia supernova rate, preliminary ASCA results for [alpha/Fe] > 0, and the ICM iron mass-to-luminosity ratio.
• A simple Virgo cluster simulation is performed to estimate the relative contributions of Type II and Type Ia supernovae to the ICM iron mass.
• The model uses standard nucleosynthesis yields and assumes no change in Type Ia progenitor models or yields, isolating the IMF as the key variable.

Experimental results

Research questions

• RQ1 How does the choice of initial mass function affect the predicted [O/Fe] ratio in the intracluster medium?
• RQ2 What fraction of the observed iron mass in the ICM can be attributed to Type II versus Type Ia supernovae?
• RQ3 Can a single IMF shape reconcile the observed iron mass-to-luminosity ratio and the [alpha/Fe] ratio in the ICM without altering Type Ia progenitor assumptions?
• RQ4 Why do some models predict positive [alpha/Fe] ratios while others predict negative ones, despite similar nucleosynthesis inputs?
• RQ5 What constraints does the observed ICM composition place on the form of the stellar initial mass function?

Key findings

• The initial mass function has a quantitatively crucial influence on the evolution of ICM abundance ratios, particularly [O/Fe].
• Flatter-than-Salpeter initial mass functions (x ≈ 1) are required to reproduce the observed [alpha/Fe] > 0 and iron mass-to-luminosity ratio in the ICM.
• The model with a flatter IMF successfully matches the preliminary ASCA results showing [alpha/Fe] > 0 in the ICM.
• In a Virgo cluster simulation, approximately 70% of the ICM iron mass originates from Type II supernovae, while 30% comes from Type Ia supernovae.
• The same IMF that fits the abundance ratios also reproduces the observed iron mass-to-luminosity ratio, indicating consistency across multiple observational constraints.
• The study shows that opposite trends in [alpha/Fe] (positive vs. negative) can be produced solely by changing the IMF, even with identical Type Ia supernova assumptions and yields.