A Deep Chandra ACIS Study of NGC 4151. II. The Innermost Emission Line Region and Strong Evidence for Radio Jet-NLR Cloud Collision

TL;DR

This study uses high-resolution X-ray imaging to investigate the innermost emission line region of NGC 4151, revealing jet-cloud interactions, collisionally ionized hot gas, and constraining the origin of Fe Kalpha emission.

Contribution

It provides new evidence for jet-induced gas heating and interaction in the nuclear region of NGC 4151, with detailed spatial and spectral analysis of emission lines.

Findings

Evidence of jet-gas cloud interactions and enhanced X-ray emission.

Detection of collisionally ionized hot gas in the inner region.

Constraints on the origin and spatial extent of Fe Kalpha emission.

Abstract

We have studied the X-ray emission within the inner 150 pc radius of NGC 4151 by constructing high spatial resolution emission line images of OVII, OVIII, and NeIX. These maps show extended structures that are spatially correlated with the radio outflow and optical [OIII] emission. We find strong evidence for jet--gas cloud interaction, including morphological correspondences with regions of X-ray enhancement, peaks of near-infrared [FeII] emission, and optical clouds. In these regions, moreover, we find evidence of elevated NeIX/OVII ratios; the X-ray emission of these regions also exceeds that expected from nuclear photoionization. Spectral fitting reveals the presence of a collisionally ionized component. The thermal energy of the hot gas suggests that >0.1% of the estimated jet power is deposited into the host interstellar medium through interaction between the radio jet and the dense medium of the circum-nuclear region. We find possible pressure equilibrium between the collisionally ionized hot gas and the photoionized line-emitting cool clouds. We also obtain constraints on the extended iron and silicon fluorescent emission. Both lines are spatially unresolved. The upper limit on the contribution of an extended emission region to the Fe Kalpha emission is <5% of the total, in disagreement with a previous claim that 65% of the Fe Kalpha emission originates in the extended narrow line region.