An In-Depth Study of the Abundance Pattern in the Hot Interstellar Medium in NGC 4649

Abstract

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.

20 pages, including 19 figures, uses emulateapj.cls; accepted for publication in ApJ

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• Half-Megasecond Chandra Spectral Imaging of the Hot Circumgalactic Nebula around Quasar Mrk 231
• Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies
• On the radial profile of gas-phase Fe/α ratio around distant galaxies
• Spectral Implications of Atomic Uncertainties in Optically-thin Hot Plasmas
• Constraining the Physical State of the Hot Gas Halos in NGC 4649 and NGC 5846
• Abundance Patterns in the Interstellar Medium of Early-type Galaxies Observed with Suzaku
• The cycle of metals in the infalling elliptical galaxy NGC 1404
• HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z = 0.4