Silicate emission in a type-2 quasar: JWST/MIRI constraints on torus geometry and radiative feedback

Type-2 quasars (QSO2s) are active galactic nuclei (AGN) seen through a significant amount of dust and gas that obscures the central supermassive black hole and the broad line region. Despite this, recent mid-infrared spectra of the central 0.5–1.1 kpc of five QSO2s at z ∼ 0.1, obtained with the MRS module of JWST/MIRI, revealed 9.7, 18, and 23 μm silicate features in emission in two of them. This indicates that the high angular resolution of JWST/MIRI now allows us to peer into their nuclear region, exposing some of the directly illuminated dusty clouds that produce silicate emission. To test this, we fit the nuclear mid-infrared spectrum of the QSO2 with the strongest silicate features, J1010, with two different sets of torus models implemented in an updated version of the Bayesian tool <ns0:monospace>BayesClumpy</ns0:monospace>. These are the CLUMPY and the CAT3D-WIND models. The CAT3D-WIND model is preferred by the observations based on the marginal likelihood and fit residuals, although the two torus models successfully reproduce the spectrum by means of intermediate covering factors (C$ _{\mathrm{T}} = 0.45\pm^{0.26}_{0.18} $ and C$ _{\mathrm{T}} = 0.66\pm^{0.16}_{0.17} $ for the CLUMPY and CAT3D-WIND models) and low inclinations ($ \mathrm{i} = 50{\circ}\pm^{8{\circ}}_{9{\circ}} $ and $ \mathrm{i} = 13{\circ}\pm^{7{\circ}}_{6{\circ}} $). Indeed, four of the five QSO2s with JWST/MIRI observations, including J1010, are in the blowout or “forbidden” region of the Eddington ratio-column density diagram, indicating that they are actively clearing gas and dust from their nuclear regions, leading to reduced covering factors. This is in contrast with Seyfert 2 galaxies observed with JWST, which are in the “permitted” regions of the diagram and show 9.7 μm silicate features in absorption. This supports a scenario where the more luminous the AGN and the higher their Eddington ratio, the lower the torus covering factor, driven by radiation pressure on dusty gas.