An XMM-Newton Observation of the Galaxy Group NGC 5044: Abundance profiles, Intrinsic Absorption, and Implications

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Abstract
(Abridged) We present an analysis of a new XMM observation of the galaxy group NGC 5044, which has been previously interpreted as a massive cooling flow. Within r ~ 30 kpc, where T is changing rapidly, the quality of the deprojected spectral fits to the EPIC MOS data is notably superior to their un-deprojected counterparts. Using a simple gaussian emission measure model within the three inner 1-arcmin-wide spatial bins, we measure in each bin the narrow T distribution expected for the single-phase T gradient. A multiphase cooling flow, which implies a much wider T distribution, is a poor fit to the XMM data. The Fe abundance exhibits a prominent gradient where Z_Fe ~ 1 Z_solar within r ~ 5 arcmin (50 kpc) and falls to Z_Fe ~ 0.35 Z_solar at r ~ 100 kpc. The near-solar values confirm that the very sub-solar Fe abundances obtained previously are the result of an ``Fe Bias'' arising from fitting isothermal models to multi-T spectra. We reproduce previous ASCA results and demonstrate explicitly the Fe Bias for NGC 5044 by fitting models to the MOS spectra accumulated within a circle of radius 5 arcmin. Consequently, the ``Iron Discrepancy'' raised by Arimoto et al. can be attributed partially to previous incorrect X-ray measurements of Fe abundances due to the Fe Bias. Models without intrinsic absorption give Mg/O ratios of 5-7 solar in the central bins which substantially exceed the values of 0.8-0.9 solar expected from both SNIa and SNII. Only a warm absorber gives Mg/O ratios near solar consistent with SN enrichment. The apparent absence of multiphase cooling in NGC 5044 is incompatible with traditional gasdynamical models that are globally flowing inward, but the modest central metal enrichment observed in NGC 5044 is also incompatible with outflowing models.

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