The near-infrared silhouette of the Flying Saucer edge-on disc revealed by the JWST JEDIce program

Aims. Edge-on discs offer a unique opportunity to probe radial and vertical dust and gas distributions in the protoplanetary phase. This study aims to investigate the distribution of micron-sized dust particles in the Flying Saucer in Rho Ophiuchi by leveraging the unique observational conditions of a bright infrared background that enables the edge-on disc to be seen in both silhouette and scattered light at specific wavelengths. Methods. We used NIRSpec IFU observations from the JWST Edge-on Disc Ice program (JEDIce) of the Flying Saucer serendipitously observed against a Polycyclic Aromatic Hydrocarbons-emitting background to constrain the dust distribution and grain sizes via radiative transfer modelling. Results. The observation of the Flying Saucer in silhouette at 3.29 μm reveals that the midplane radial extent of small dust grains is ∼235 au, i.e. larger than the large-grain disc extent previously determined to be 190 au from millimetre data. The scattered light observed in emission probes micron-sized icy grains at large vertical distances above the midplane. The vertical extent of the disc silhouette is similar at visible, near-IR, and mid-IR wavelengths, corroborating the conclusion that dust settling is inefficient for grains as large as tens of microns, both vertically and radially.