XMM-Newton observations of NGC 507:: Supersolar metal abundances in the hot interstellar medium

We present the results of the X-ray XMM-Newton observations of NGC 507, a dominant elliptical galaxy in a small group of galaxies, and report supersolar metal abundances of both Fe and alpha-elements in the hot interstellar medium ( ISM) of this galaxy. These results are robust in that we considered all possible systematic effects in our analysis. We find Z(Fe) = 2-3 times solar inside the D-25 ellipse of NGC 507. This is the highest Z(Fe) reported so far for the hot halo of an elliptical galaxy; this high iron abundance is fully consistent with the predictions of stellar evolution models, which include the yield of both Type II and Type Ia supernovae (SNe). Our analysis shows that abundance measurements are critically dependent on the selection of the proper emission model. The spatially resolved, high-quality XMM-Newton spectra provide enough statistics to formally require at least three emission components in each of four circumnuclear concentric shells (within 5' or 100 kpc): two soft thermal components indicating a range of temperatures in the hot ISM plus a harder component, consistent with the integrated output of low-mass X-ray binaries (LMXBs) in NGC 507. The two-component (thermal+ LMXB) model customarily used in past studies yields a much lower Z(Fe), consistent with previous reports of subsolar metal abundances. This model, however, gives a significantly worse fit to the data (F-test probability < 0.0001). The abundance of alpha-elements (most accurately determined by Si) is also found to be supersolar. The alpha-element - to - Fe abundance ratio is close to the solar ratio, suggesting that similar to 70% of the iron mass in the hot ISM originated from Type Ia SNe. The alpha-element - to - Fe abundance ratio remains constant out to at least 100 kpc, indicating that Types II and Ia SN ejecta are well mixed on a scale much larger than the extent of the stellar body.