PDRs4All

The Orion Nebula Cluster (ONC) provides the closest example of ongoing star and planet formation in highly irradiated environments. In particular, it is a key region for studying how ultraviolet (UV) radiation from massive stars can drive mass loss in protoplanetary disks through photo-evaporation. Far-UV (FUV, energy 6<E<13.6 eV) photons heat up the gas of the disk, forming a wind of neutral gas that is a photodissociation region (PDR). We used high-angular-resolution NIRCam images from the PDRs4All program and combined them with those of the guaranteed time observation (GTO) program 1256. From these images, we extracted key information on ONC disks, such as the radii of the disks observed in silhouette against the bright background, the presence and positions of the dissociation fronts (DFs), the presence and positions of ionization fronts (IFs), intensities of Paschen α lines, and their near-infrared spectral energy distributions (SEDs). From this information we constructed a typology for ONC disks: Type I sources show an IF and DF nearly merged at the disk surface; Type II sources have their DFs at the disk surface and IFs at a distance of several tens of astronomical units from the disk; and Type III sources also have their DF at the disk surface, but show no IF. For all types of disks, we find that PAH emission traces the PDR. We established that the SEDs of candidate Jupiter-mass binary objects (JuMBOs) observed as part of the PDRs4All program are similar to the SEDs of Type III ONC disks, except for one of them, JuMBO24, which is of Type I or II. A detailed look at this SED shows that it is compatible with a young low-mass binary star with an unresolved ionized disk: a microproplyd binary. We observe that the disk radius of ONC disks, rdisk, increases with increasing projected distance to the ionizing source, dproj, following a power law, r disk ∝ dproj0.30, which is interpreted as evidence of the truncation of the disks by the photoevaporation (as reported in previous studies). The disk radii measured at infrared wavelengths appear larger than the disk radii measured at millimeter wavelengths, which is interpreted as evidence of the dust radial segregation within the disks. In agreement with theoretical models and observations of PDRs in the interstellar medium, the thermal pressure within the PDRs of ONC disk increases with the intensity of the FUV radiation field, G0, but with a flatter slope.