Core-collapse supernova enrichment in the core of the Virgo Cluster
  Using a deep (574 ks) Chandra observation of M87, the dominant galaxy of the
nearby Virgo Cluster, we present the best measurements to date of the radial
distribution of metals in the central intracluster medium (ICM). Our
measurements, made in 36 independent annuli with $\sim$250,000 counts each,
extend out to a radius r$\sim$40 kpc and show that the abundance profiles of
Fe, Si, S, Ar, Ca, Ne, Mg, and Ni are all centrally peaked. Interestingly, the
abundance profiles of Si and S - which are measured robustly and to high
precision - are even more centrally peaked than Fe, while the Si/S ratio is
relatively flat. These measurements challenge the standard picture of chemical
enrichment in galaxy clusters, wherein type Ia supernovae (SN Ia) from an
evolved stellar population are thought to dominate the central enrichment. The
observed abundance patterns are most likely due to one or more of the following
processes: continuing enrichment by winds of a stellar population pre-enriched
by SNCC products; intermittent formation of massive stars in the central
cooling core; early enrichment of the low entropy gas. We also discuss other
processes that might have contributed to the observed radial profiles, such as
a stellar initial mass function that changes with radius; changes in the
pre-enrichment of core-collapse supernova progenitors; and a diversity in the
elemental yields of SN Ia. Although systematic uncertainties prevent us from
measuring the O abundance robustly, indications are that it is about 2 times
lower than predicted by the enrichment models.
