The edge-on disk Tau042021: icy grains at high altitudes and a wind containing astronomical PAHs

Spectra of the nearly edge-on protoplanetary disks observed with the JWST have shown ice absorption bands of varying optical depths and peculiar profiles, challenging radiative transfer modelling and our understanding of dust and ice in disks. Aims. With the aim of constraining the underlying disk’s structure and evolutionary state, we build models including dust grain size, shape, and composition to reproduce JWST IFU spectroscopy of a well-characterised, massive and large edge-on disk, Tau 042021. Specifically we aim to match its spectral energy distribution, the spatial distribution of the dust and ice, the spectral characteristics of the dust continuum and ice bands profiles, as well as testing for the presence of astronomical PAH band carriers. Methods. We explore radiative transfer models using different dust grain size distributions, including grains with effective radii aeff = 0.005 − 3000 μm. Mass absorption and scattering coefficients for distributions of triaxial ellipsoidal grains are calculated using the discrete dipole approximation (DDA) for small size parameters (2πaeff/λ < 10), whereas the hollow sphere approximation is used for larger size parameters. We consider compositions including silicates, amorphous carbon, and mixtures of water, carbon dioxide, and carbon monoxide. The resulting orientation-averaged scattering matrices are input into RADMC-3D Monte Carlo radiative transfer models of Tau 042021 to simulate the spectral cubes observed with JWST-NIRSpec and MIRI. We compare the calculated optical depth distributions and profiles of the main ice bands to observations, including water at 3.05 μm, carbon monoxide at 4.67 μm, and carbon dioxide at 4.27 μm. We also compare these results to archival JWST-NIRCam and ALMA continuum images. We test three increasingly complex disk structures, starting from a standard model, first adding an extended atmosphere and then a disk wind containing astro-PAHs. Results. The observed near- to mid-infrared spectral energy distribution requires efficient scatterers, thus implying dust distributions that include grain sizes up to several tens of microns. The intensity distribution perpendicular to the disk exhibits emission profile wings extending into the upper disk atmosphere at altitudes exceeding the classical scale height expected in the isothermal hydrostatic limit.We produce ice absorption images that demonstrate the presence of icy dust grains up to altitudes high above the disk midplane, more than three hydrostatic equilibrium scale heights. We demonstrate the presence of a wind containing the carriers of astronomical PAH bands. The wind appears as an X-shaped emission at 3.3, 6.2, 7.7 and 11.3 microns, characteristic wavelengths associated with the infrared astronomical PAH bands.We associate the spatial distribution of this component with carriers of astronomical PAH bands that form a layer of emission at the interface with the H2 wind.