The kpc Scale Fe K$\alpha$ Emission in the Compton Thin Seyfert 2 Galaxy NGC 4388 resolved by Chandra

TL;DR

This study uses Chandra observations to resolve and analyze kpc-scale Fe Kα emission in the Seyfert 2 galaxy NGC 4388, revealing spatially extended structures and their relation to the AGN activity.

Contribution

First detailed spatially resolved imaging and spectral analysis of kpc-scale Fe Kα emission in NGC 4388, linking extended X-ray features to AGN activity and galactic structures.

Findings

Extended Fe Kα emission correlates with [OIV] luminosity.

Extended structures align with galactic disk and dust lane.

Differences in Fe Kα equivalent width suggest varying column densities or scattering angles.

Abstract

We present Chandra imaging and spectral observations of Seyfert 2 galaxy NGC 4388. Three extended X-ray structures around the nucleus on kpc scale are well imaged, allowing an in-depth spatially resolved study. Both the extended hard continuum and the Fe K$\alpha$ line show similar morphology, consistent with a scenario where the ionizing emission from nucleus is reprocessed by circumnuclear cold gas, resulting in a weak reflection continuum and an associated neutral Fe K$\alpha$ line. This has been seen in other Compton thick active galactic nuclei (AGN), but NGC 4388 is one of the rare cases with a lower column density ($N_{\rm H} < 1.25\times 10^{24}$ cm$^{-2}$) along the line of sight. Significant differences in equivalent width of the Fe K$\alpha$ emission line are found for the nuclear and extended regions, which could be ascribed to different column densities or scattering angles with respect to the line of sight, rather than variations in iron abundances. The north-east and west extended structures are aligned with the galactic disk and dust lane in the HST $V-H$ map, and located at the peak of molecular gas distribution. The morphology implies that the kpc-scale radio outflow may have compressed the interstellar gas and produced clumps working as the reflector to enhance line emission. Using [OIV] emission as a proxy of the AGN intrinsic luminosity, we find that both of the extended Fe K$\alpha$ emission and reflection continuum are linearly correlated with the [OIV] luminosity, indicating a connection between the AGN and the extended emission.