An In-Depth Study of the Abundance Pattern in the Hot Interstellar Medium in NGC 4649. (arXiv:1207.5814v1 [astro-ph.CO])

An In-Depth Study of the Abundance Pattern in the Hot Interstellar Medium in NGC 4649. (arXiv:1207.5814v1 [astro-ph.CO]):
We present our X-ray imaging spectroscopic analysis of data from deep Suzaku
and XMM-Newton Observatory exposures of the Virgo Cluster elliptical galaxy NGC
4649 (M60), focusing on the abundance pattern in the hot interstellar medium
(ISM). All measured elements show a radial decline in abundance, with the
possible exception of Oxygen. We construct steady state solutions to the
chemical evolution equations that include infall in addition to stellar mass
return and SNIa enrichment, and consider recently published SNIa yields. By
adjusting a single model parameter to obtain a match to the global abundance
pattern in NGC 4649 we infer that introduction of subsolar metallicity external
gas has reduced the overall ISM metallicity and diluted the effectiveness of
SNIa to skew the pattern towards low alpha-to-Fe ratios, and estimate the
combination of SNIa rate and level of dilution. Evidently, newly-introduced gas
is heated as it is integrated into, and interacts with, the hot gas that is
already present. These results indicate a complex flow and enrichment history
for NGC 4649, reflecting the continual evolution of elliptical galaxies beyond
the formation epoch. The heating and circulation of accreted gas may help
reconcile this dynamic history with the mostly passive evolution of elliptical
stellar populations. In an appendix we examine the effects of the recent
updated atomic database AtomDB in spectral fitting of thermal plasmas with hot
ISM temperatures in the elliptical galaxy range.