The subarcsecond mid-infrared view of local active galactic nuclei: III. Polar dust emission

TL;DR

This study investigates the prevalence of polar dust emission in local AGN, finding that a significant portion shows extended MIR emission aligned with the system axis, challenging traditional torus models.

Contribution

It provides evidence that most MIR emission in Seyfert galaxies originates from polar dust, suggesting a need to revise the standard AGN infrared emission paradigm.

Findings

At least 40% of Seyferts show extended MIR emission.

Extended MIR emission aligns with the system axis in 18 out of 21 cases.

The MIR emission correlates with [OIV] fluxes, indicating a connection to the AGN activity.

Abstract

Recent mid-infrared (MIR) interferometric observations showed in few active galactic nuclei (AGN) that the bulk of the infrared emission originates from the polar region above the putative torus, where only little dust should be present. Here, we investigate whether such strong polar dust emission is common in AGN. Out of 149 Seyferts in the MIR atlas of local AGN (Asmus et al.), 21 show extended MIR emission on single dish images. In 18 objects, the extended MIR emission aligns with the system axis position angle, established by [OIII], radio, polarisation and maser based position angle measurements. The relative amount of resolved MIR emission is at least 40 per cent and scales with the [OIV] fluxes implying a strong connection between the extended continuum and [OIV] emitters. These results together with the radio-quiet nature of the Seyferts support the scenario that the bulk of MIR emission is emitted by dust in the polar region and not by the torus, which would demand a new paradigm for the infrared emission structure in AGN. The current low detection rate of polar dust in the AGN of the MIR atlas is explained by the lack of sufficient high quality MIR data and the requirement for the orientation, NLR strength and distance of the AGN. The James-Webb Space Telescope will enable much deeper nuclear MIR studies with comparable angular resolution, allowing us to resolve the polar emission and surroundings in most of the nearby AGN.