High-resolution X-ray imaging and spectroscopy of the core of NGC 4945 with XMM-Newton and Chandra

Abstract

We utilize the complementary capabilities of XMM-Newton and Chandra to conduct a detailed imaging and spectral study of the nearby galaxy NGC 4945 focusing on its nucleus and immediate surroundings (within ~ kpc of the nucleus). A complex morphology is revealed including a predominantly hard, but partially resolved, nuclear source plus a spectrally soft, conically shaped X-ray `plume', which extends 30 arcsec (500 pc) to the north-west. In NGC 4945 our direct view of the active galactic nucleus (AGN) is blocked below ~10 keV by extremely heavy line-of-sight absorption, and the observed X-ray spectrum is dominated by multi-temperature thermal emission associated with the nuclear starburst and the X-ray plume. Nevertheless the signature of the AGN is present in the form of a neutral Compton reflection component and a 6.4 keV fluorescent iron Kα line. We conjecture that the site of the continuum reprocessing is the far wall of a highly inclined molecular torus, a geometry which is consistent with the presence of H₂O megamaser emission in this source. The soft spectrum (~0.6 keV) and limb-brightened appearance of the X-ray plume suggest an interpretation in terms of a mass-loaded superwind emanating from the nuclear starburst.