Discovery of kpc-scale semi-relativistic Fe K emission in NGC 5728

We present Chandra ACIS-S imaging spectroscopy results of the extended (300 -1600 pc) hard X-ray emission of NGC 5728, the host galaxy of a Compton thick active galactic nucleus (CT AGN). We find spectrally and spatially-resolved features in the Fe Kα complex (5.0-7.5 keV), redward and blueward of the neutral Fe line in the extended ionized bicone. A simple phenomenological fit of a power law plus Gaussians gives a significance of 5.4σ and 3.7σ for the red and blue features, respectively. Spectral fits employing a set of physically motivated models confirm a significance ≥3σ for the red wing. The significance of the blue wing may be diminished by the presence of rest frame highly ionized Fe XXV (at 6.7 keV) and Fe XXVI (at 6.9keV) lines (1.4σ-3.7σ range in significance). A detailed investigation of the Chandra ACIS-S point spread function (PSF) and comparison with the observed morphology demonstrates that these red and blue features are radially extended (~5′′, ~1 kpc) along the optical bicone axis. If the wings emission is due solely to redshifted and blueshifted high-velocity neutral Fe Kα, then the implied line-of-sight velocities are symmetrically ~0.1c, and their fluxes are consistent with being equal. This outflow has deprojected velocities ~100x larger than the outflows detected in optical spectroscopic studies, potentially dominating the kinetic feedback power.