The Kiloparsec-scale Fe Ka Emission in the Compton-thin Seyfert 2 Galaxy NGC 4388 Resolved by Chandra

We present imaging and spectral analysis of the combined similar to 48 ks Chandra observations of Seyfert 2 galaxy NGC 4388. Compared with previous studies, three prominent extended X-ray structures around the nucleus on a kiloparsec-scale are well imaged, allowing an in-depth spatially resolved study. Both the extended hard continuum (4-6 keV) and the Fe K alpha line (6.2-6.7 keV) show similar morphology, consistent with a scenario where the ionizing emission from the 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-H < 1.25 x 10(24) cm(-2)) along the line of sight. Significant differences in equivalent width of the Fe K alpha emission line (up to a factor of 3) are found for the nuclear and extended regions. Such a difference could be ascribed to different column densities or scattering angles with respect to the line of sight, rather than variations in iron abundances. The northeast and west extended structures appear to be aligned with the larger-scale galactic disk and dust lane in the HST V - H color map, and are located at the peak of molecular gas distribution. The morphology of remaining extended features likely traces edges of a known radio jet, indicating that the outflow at the kiloparsec-scale may have compressed the interstellar gas and produced clumps working as the reflector to enhance line emission. In addition, using [O iv] 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 [O iv] luminosity, which indicates a connection between the central AGN and the extended emission.

Automated summary

This study presents imaging and spectral analysis of Seyfert 2 galaxy NGC 4388 based on around 48 ks Chandra observations. The extended X-ray structures and Fe K alpha line morphology suggest reprocessing of ionizing emission from the nucleus by circumnuclear gas. The differences in Fe K alpha emission line equivalent width between nuclear and extended regions may be due to varying column densities or scattering angles, rather than iron abundances. The extended structures appear to align with the galactic disk and are located at the peak of molecular gas distribution, indicating a connection between central AGN and extended emission.