New evidence for the dusty wind model: Polar dust and a hot core in the type-1 Seyfert ESO$\,$323-G77

TL;DR

Infrared interferometry of Seyfert galaxy ESO 323-G77 reveals polar dust emission and a hot core, challenging the classical torus model and supporting the dusty wind model in AGN unification schemes.

Contribution

This study provides new interferometric data and morphological analysis of ESO 323-G77, demonstrating polar dust emission consistent with the dusty wind model, unlike traditional torus models.

Findings

65% of mid-IR flux is unresolved, indicating a compact core.

Dust emission is elongated along the polar direction, confirming polar extension.

A dusty wind model fits the data better than a classical torus model.

Abstract

Infrared interferometry of Seyfert galaxies has revealed that their warm ($300-400\,$K) dust emission originates primarily from polar regions instead of from an equatorial dust torus as predicted by the classic AGN unification scheme. We present new data for the type 1.2 object ESO$\,$323-G77 obtained with the MID-infrared interferometric Instrument (MIDI) and a new detailed morphological study of its warm dust. The partially resolved emission on scales between $5$ and $50\,$mas ($1.6-16\,$pc) is decomposed into a resolved and an unresolved source. Approximately $65\%$ of the correlated flux between $8$ and $13\,\mu\mathrm{m}$ is unresolved at all available baseline lengths. The remaining $35\%$ is partially resolved and shows angular structure. From geometric modelling we find that the emission is elongated along a position angle of $155^\circ\pm14^\circ$ with an axis ratio (major/minor) of $2.9\pm0.3$. Because the system axis is oriented in position angle $174^\circ\pm2^\circ$, we conclude that the dust emission of this object is also polar extended. A $\textit{CAT3D-WIND}$ radiative transfer model of a dusty disk and a dusty wind with a half opening angle of $30^\circ$ can reproduce both the interferometric data and the SED, while a classical torus model is unable to fit the interferometric data. We interpret this as further evidence that a polar dust component is required even for low-inclination type 1 sources.