James Webb Space Telescope Feed Post

Dust beyond the torus: Revealing the mid-infrared heart of local Seyfert ESO 428-G14 with JWST/MIRI

Left: RGB composite image of the JWST/MIRI images of ESO 428-G14, where red, green, and blue channels correspond to F1500W, F1000W, and F560W filters, respectively. The combination of these three filters reveals the MIR structure of the circumnuclear disk along with the small-scale nuclear extensions. The field of view (FOV) is ~ 25'' across. The strong diffraction spikes are due to the bright central point-like source, which has not been subtracted in the version of the images used for this composite. Right: Optical HST image of ESO 428-G14 in the F814W filter over the same FOV as the JWST colour composite from the left panel. Zooming into the inner 2'' × 2'' region, the radio jet traced by the VLA 15 GHz emission is displayed in the bottom right of the figure. Abstract: Polar dust has been discovered in a number of local Active Galactic Nuclei (AGN), with radiation-driven torus models predicting a wind to be its main driver. However, little is known about its characteristics, spatial extent, or connection to the larger scale outflows. We present the first JWST/MIRI study aimed at imaging polar dust by zooming onto the heart of ESO 428-G14, part of the GATOS survey of local AGN. We clearly detect extended mid-infrared (MIR) emission within 200 pc from the nucleus. This polar structure is co-linear with a radio jet and lies perpendicular to a molecular gas lane that feeds and obscures the nucleus. The morphology of the MIR structure bears a striking resemblance to that of gas ionised by the AGN in the narrow-line region (NLR). We demonstrate that part of this spatial correspondence is due to contamination within the JWST filter bands from strong emission lines. Correcting for the contamination using ancillary spectroscopy, we find the morphology of the dust continuum to be asymmetric around the nucleus and more compact, though still clearly extended out to r ~ 100 pc. We estimate a temperature of the emitting dust of ~ 120 K. Using simple models, we find that the heating of small dust grains (~ 0.01 microns) by the radiation from the central AGN and/or radiative jet-induced shocks is responsible for the extended MIR emission. Large-grained dust, predicted by models of radiation-driven dusty winds from the torus, is unlikely to be important. This has important implications for scales to which AGN winds can carry dust and dense gas out into their host galaxies.