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

TL;DR

This study analyzes the elemental abundance patterns in the hot interstellar medium of NGC 4649 using X-ray data, revealing a complex enrichment history influenced by external gas infall and supernova activity.

Contribution

It introduces a chemical evolution model incorporating external gas infall and updated SNIa yields to explain the observed abundance patterns in NGC 4649.

Findings

Radial decline in element abundances with possible exception of Oxygen

External gas infall dilutes ISM metallicity and affects SNIa enrichment signatures

Updated atomic database impacts spectral fitting accuracy

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.