Shocks, Winds, and a Torus: The Large Binocular Telescope Interferometer (LBTI) Resolves the Active Nucleus of NGC 4151

TL;DR

This study uses high-resolution mid-infrared imaging from the LBTI to resolve the dusty torus and surrounding structures in NGC 4151, revealing details about dust heating mechanisms and comparing it to NGC 1068 to test AGN models.

Contribution

First high-resolution MIR imaging of NGC 4151 with LBTI bridging previous data, revealing the torus and shock heating effects, and comparing AGN structures to test the Unified Model.

Findings

Resolved a 32 pc dusty torus in NGC 4151.

Detected shock heating from radio jets affecting dust.

Found the torus size scales with luminosity as r∝L^{0.5}.

Abstract

We present mid-infrared (MIR) observations of the Seyfert 1 galaxy NGC 4151 using the Large Binocular Telescope Interferometer (LBTI). We took open-loop Fizeau images with 66-104 mas (5.8-9.1 pc) resolution in the N-band (at $8.7$ and $10.5~\mu m$), using the full resolution of the LBTI -- equivalent to that of a 28.8 m telescope. These images were complemented by AO imaging in the LM-bands ($3.7$ and $4.8~\mu m$), with 50-62 mas (4.4-5.4 pc) resolution. These images bridge the scales between previous Very Large Telescope Interferometer (VLTI)/MIDI and VLT/VISIR data, delivering ELT-like imaging resolution in the N-band. We resolve a dusty torus, (diameter 32 pc, PA$=125^{\circ}$), and detect dusty clouds within the narrow line region. Matching the resolution across four bands, we measured spatially-resolved SEDs of the central $\sim 100$ pc. Modified blackbody fitting revealed dust temperature and extinction profiles, indicating both heating from the accretion disk and additional shock heating due to the radio jet. The spatial coincidence of ionized emission (e.g., [Fe II] and [O III]), extended MIR structures, and radio features further supports the interpretation of shock heating. Comparison with NGC 1068 tests the Unified Model of Active Galactic Nuclei (Unified Model of AGN): Structures are similar, despite differences in orientation and Eddington ratio. NGC 4151's torus is smaller than NGC 1068's following a $r\propto L^{0.5}$ scaling. These thirty-meter-telescope class observations of NGC 4151 and NGC 1068 highlight the need to revise MIR radiative transfer models of AGN to account for jet-related heating.