ar X iv : a st ro - p h / 03 10 76 8 v 1 2 7 O ct 2 00 3 Constraints on SN Ia Progenitors and ICM enrichment from field and cluster SN rates

The iron mass in galaxy clusters is about 6 times larger than could have been produced by core-collapse SNe, assuming the stars in cluster galaxies formed with a standard IMF. Type-Ia SNe have been proposed as the alternative dominant iron source. We use our HST measurements of the cluster SN-Ia rate at high redshift to study the cluster iron enrichment scenario. The measurements can constrain the star-formation epoch and the SN-Ia progenitor models via the mean delay time between the formation of a stellar population and the explosion of some of its members as SNe-Ia. The low observed rate of cluster SNe-Ia at z ∼ 1 pushes back the star-formation epoch in clusters to z > 2, and implies a short delay time. We also show a related analysis for high-z field SNe which implies, under some conditions, a long SN-Ia delay time. Thus, cluster enrichment by core-collapse SNe from a top-heavy IMF may remain the only viable option. 1 The SN Ia Rate in z ≤ 1 Galaxy Clusters and the Source of Cluster Iron The iron mass in galaxy clusters is about 6 times larger than could have been produced by core-collapse supernovae (SNe), assuming the stars in the cluster formed with a standard initial mass function (IMF; e.g., Renzini 1997). SNe Ia have been proposed as the alternative dominant iron source. Different SN Ia progenitor models predict different " delay functions " , between the formation of a stellar population and the explosion of some of its members as SNe Ia. We use updated measurements of the total iron mass-to-light ratio in rich clusters to normalize the predicted SN Ia rate in clusters vs. redshift, using the delay function parameterization of Madau, Della Valle, & Panagia (1998). We then use our previous measurements of the cluster SN Ia rate at high redshift (Gal-Yam, Maoz, & Sharon 2002) to constrain SN Ia progenitor models and the star-formation epoch in clusters. The low observed rate of cluster SNe Ia at z ∼ 0 − 1 (Fig. 1) means that, if SNe Ia produced the observed amount of iron, they must have exploded at even higher z. This puts a > 95% upper limit on the mean SN Ia delay time of τ < 2 Gyr (< 5 Gyr) if the stars in clusters formed at z f < 2 (z f < 3), assuming Ho = 70 km s …