Radial dust distributions and obscuring geometry in AGN from JWST/MIRI spectroscopy

Abstract

The spatial distribution of obscuring dust in active galactic nuclei (AGN) is critical for distinguishing between static torus models and dynamical disk-wind scenarios. To constrain this geometry, we forward-model the rest-frame $5$--$14\mu \mathrm{m}$ JWST/MIRI MRS spectra of 25 local AGN using a three-dimensional, axisymmetric radiative-transfer library combined with empirical starburst templates. Using a grid-based inference framework, we systematically compare radial dust-density laws of the form $n(r)\propto r^{-p}$ over the range $p=0.5$--$2.0$. Our model comparison strongly favours shallow radial profiles at the sample level: 20 sources achieve their largest statistical weight at $p=0.5$, and 21 accumulate more than half of their combined density-law weight at $p\le 1$. This tendency remains robust even when the likelihood power $\beta$ is varied, although the preferred profile of individual sources can change. Furthermore, the $9.7\mu \mathrm{m}$ silicate feature exhibits a distinct trend: absorption minima remain near $9.7\mu \mathrm{m}$, whereas four observed emission maxima are shifted redward by approximately $0.8$--$1.3\mu \mathrm{m}$. These results favour relatively extended MIR-emitting dust distributions rather than strictly compact geometries, and suggest that an interplay of radiative-transfer effects and intrinsic dust grain properties drives the observed spectral diversity.

18 pages, 9 figures