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

Abstract

We forward-model rest-frame $8$--$20\,μ\mathrm{m}$ JWST/MIRI MRS spectra of 25 active galactic nuclei (AGN) with a three-dimensional radiative-transfer library in order to compare radial dust-density laws of the form $n(r)\propto r^{-p}$ over $p=0.5$--$2.0$. Within our tempered grid-based comparison, the model scores do not identify a single radial profile that is preferred for all sources. Instead, 20 of the 25 sources have their largest normalized tempered weights at $p\leq1$, while five have their highest scores at $p\geq1.5$, suggesting that both more extended and more centrally concentrated effective MIR-emitting dust distributions may be represented in the sample. The silicate feature shows a second systematic trend: absorption minima remain close to the canonical $9.7\,μ\mathrm{m}$ wavelength, whereas emission peaks are shifted redward by about $1\,μ\mathrm{m}$, consistent with a combination of radiative-transfer effects and dust processing in the illuminated inner regions. By contrast, the effective obscuring-geometry parameters are more tightly clustered within the adopted grid: the fitted opening-angle values cluster at $30^\circ$--$40^\circ$, and 24 sources have the intermediate radial-extent grid value $Y = 100$. These results suggest that variations in the radial dust distribution and effective dust properties are important contributors to the observed MIR spectral diversity, while the fitted opening-angle parameter is comparatively clustered within the adopted model framework.