Cluster Abundances (PPT, PDF)
Most of the baryonic matter in clusters resides in a 107 - 108K intracluster medium (ICM) which contains both primordial material, not yet incorporated into galaxies, and enriched material from galactic outflows. Standard models of chemical evolution that reproduce abundances in Milky Way stars fail to explain the abundance pattern in the ICM (e.g., Matsushita et al. 2007, Finoguenov et al. 2002; Fig. 1.3). Heavy elements are created in and expelled from spheroidal galaxies with very different characteristics and histories from the Milky Way. Therefore, the detailed nature of star formation in these galaxies must differ from that in the Milky Way -- perhaps requiring novel sources of enrichment such as primordial Pop. III stars (Baumgartner et al. 2006) or a new variety of Type I supernova (de Plaa et al. 2007).
SXS determines abundances of key diagnostic elements that are currently inaccessible because of low equivalent widths (i.e., N, Al, Ca, and Ar) or blending with the vast number of Fe L shell transitions (Ne and Mg). Because of its distinct production channels, N is a particularly accurate diagnostic of the stellar initial mass function (IMF), while the Ca/Ar ratio is sensitive to the Type Ia explosion mechanism (de Plaa et al. 2007). Simulations show that a 300 ksec observation of any of the 40 brightest hot clusters yields an N abundance accurate to ± 20%, far better than any current observatory in any waveband.
SXS observations yield, for the first time, abundance measurements accurate to ±10% of O, Ne, and Mg to z~0.2 and ±20% to z~0.4. Fe and Si abundances can be determined in bright clusters with z > 1. These measurements distinguish between different enrichment models, constrain models of the IMF, and determine key characteristics of Type Ia supernovae, such as the explosion mechanism, efficiency of binary progenitor formation, and distribution of delay times.
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| Cluster abundances averaged from multiple 10-100 ksec XMM-Newton observations, fit with a combination of observed SN Ia ejecta from Tycho (green) and theoretical core-collapse models (blue) (after de Plaa et al. 2007). Surprisingly, no combination of these two sources explains the observed ratios of elements, in particular [Ar/Fe] and [Ca/Fe]. | The average range for [Ca/Fe] is shown in red, with values for individual clusters from XMM (black) and SXS simulations (blue). SXS enables tests on a per-cluster basis, rather than as an average. |
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