[Paper Review] Galactic chemical evolution in hierarchical formation models - II. The Intracluster Medium

Matías Arrigoni, S. C. Trager+1 more|arXiv (Cornell University)|Jun 6, 2010

Gamma-ray bursts and supernovae3 citations

TL;DR

This paper extends a semi-analytic galaxy formation model to predict intracluster medium (ICM) metallicity and abundance ratios in a hierarchical structure formation framework. By introducing direct metal injection into the hot ICM ("hot enrichment") and increasing the SN Ia rate, the model successfully reproduces observed ICM iron abundance and elemental ratios, resolving a key deficit in prior models.

ABSTRACT

We use the cosmological semi-analytic model (SAM) for galaxy formation presented in Paper I to study the metallicities and abundance ratios of the intracluster medium (ICM) within the hierarchical structure formation paradigm. By requiring a slightly flat IMF (x=1.15) and a two-population delay-time-distribution (DTD) for SN Ia explosions we found previously that this model is able to reproduce the abundance ratios and supernova rates of early-type galaxies in the local Universe. Predictions for elemental abundances in the ICM pose a further test of the model. We find that with the fiducial model from Paper I the overall metal content of the ICM is too low, although the abundance ratios are in good agreement with the data. However, we find that allowing a fraction of the metal-enriched material ejected by stars to be deposited directly into the hot ICM, instead of being deposited into the cold ISM, appears to be a plausible and physically-motivated solution.

Motivation & Objective

• To test whether the semi-analytic model (SAM) from Paper I can reproduce observed intracluster medium (ICM) metallicity and abundance ratios in clusters.
• To address the persistent underprediction of ICM iron abundance in hierarchical galaxy formation models.
• To investigate whether direct deposition of metal-enriched stellar ejecta into the hot ICM—bypassing the cold ISM—can resolve the discrepancy.
• To assess the consistency of the modified model with observed galaxy abundance ratios and supernova rates.
• To evaluate whether the new physics affects the global baryon budget or star formation efficiency in halos.

Proposed method

• Adapt the semi-analytic model (SAM) from Paper I, which already reproduces local galaxy abundance ratios using a slightly flat IMF (x=1.15) and a bimodal delay-time distribution (DTD) for SN Ia.
• Introduce 'hot enrichment' by allowing 80% of metal-rich ejecta from stars to be deposited directly into the hot ICM instead of the cold ISM.
• Adjust the binary fraction parameter A to increase the SN Ia rate, testing values A=0.03 (fiducial) and A=0.04 to improve iron production.
• Use updated SN Ia yields (Iwamoto et al. 1999, WDD3) to reduce excessive nickel production compared to prior yields.
• Compare model predictions for ICM metallicity, [α/Fe], and SN Ia rates against X-ray observations of nearby clusters.
• Validate the model's impact on galaxy properties by comparing predicted [α/Fe] and SN Ia rates with local galaxy data.

Experimental results

Research questions

• RQ1 Can the hierarchical galaxy formation model from Paper I reproduce observed intracluster medium (ICM) metallicity and abundance ratios?
• RQ2 Why is the ICM iron abundance systematically too low in the fiducial model, and what physical mechanism can resolve this?
• RQ3 Does direct injection of metals into the hot ICM (hot enrichment) improve agreement with ICM observations?
• RQ4 How does increasing the SN Ia rate affect the consistency of the model with both ICM and galaxy observations?
• RQ5 Does the inclusion of hot enrichment alter the global baryon budget or star formation efficiency in cluster halos?

Key findings

• The fiducial model from Paper I underpredicts the ICM iron abundance, despite successfully matching galaxy abundance ratios.
• Introducing 'hot enrichment'—where 80% of metal-rich ejecta are deposited directly into the hot ICM—significantly improves the agreement with observed ICM metallicity.
• A higher SN Ia rate (A=0.04 instead of A=0.03) is required to match the observed ICM iron content, and this value remains consistent with SN Ia rate observations as a function of specific star formation rate.
• The model successfully reproduces the observed flat trend of ICM abundance ratios with cluster temperature, matching observational data.
• For some elements (O, Si, Ca, Ni), the zero-point of abundance ratios is reproduced remarkably well; others (Ar, S) agree marginally, while Ne and Mg are underpredicted.
• The [Mg/Fe] ratio can be corrected by increasing the Mg yield from SN II, as done with standard WW95 yields, suggesting that yield uncertainties may contribute to discrepancies in other elements.