Kiloparsec-scale Neutral Iron K<i>α</i> 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 K α emission due to the AGN activity. We report the discovery of very extended Fe K α 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 galactic disk by ∼60° 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 K α is extended on kiloparsec-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 K α emission arose from a period of AGN eruption several million years ago—a relic of a past AGN ejection episode.