Kpc-Scale Neutral Iron Kα Emission in the Starburst-AGN NGC 4945: a Relic AGN Outflow?
Abstract
NGC 4945 contains a well-known heavily obscured active galactic nucleus (AGN) at its core, with prior reports of strong nuclear and off-nuclear neutral Fe Kα emission due to the AGN activity. We report the discovery of very extended Fe Kα emission with the XMM-Newton EPIC pn in a 5 kpc by 10 kpc region that is misaligned with the plane of the inclined optical galaxy disk by 60 degrees in projection. After a careful consideration of the crowded center of the galaxy and numerous unresolved hard X-ray sources present, we estimate that 15% of the Fe Kα is extended on kpc-sized scales. The overall size and misalignment of the region follows an unusual pattern of radio polarization that is not typical of starbursts or normal disk galaxies but has been interpreted as possibly due to AGN activity. We suggest that the extended Fe Kα emission arose from a period of AGN eruption several million years ago - a relic of a past AGN ejection episode.
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