PDRs4All XXI. JWST-NIRCam Photometric properties of protoplanetary disks in the Orion Nebula Cluster

TL;DR

The paper leverages JWST/NIRCam imaging to study protoplanetary disks and JuMBOs in the ONC, introducing a three-type typology based on the relative positions of ionization and dissociation fronts. It shows that disk radii increase with the projected distance to the ionizing source and with the FUV field, consistent with external photoevaporation, while IR disk sizes exceed millimeter radii, indicating dust radial segregation. SEDs corroborate the typology, with Type I/II disks showing strong Pa α and Br α features and Type III disks being more blackbody-like; JuMBO24 stands out as a likely young low-mass binary with irradiated disks. The study also demonstrates that the thermal pressure in disk PDRs grows with $G_0$ in a way that mirrors ISM PDRs but with a flatter slope, underscoring nuanced PDR physics in disk winds and the broader impact of UV radiation on disk evolution in clustered environments.

Abstract

We use the high angular resolution NIRCam images from the PDRs4All program, combined with those of GTO program 1256, to extract key properties of disks in the Orion Nebula Cluster. We measure disk radii in silhouette against the bright background, identify dissociation fronts (DFs) and ionization fronts (IFs), determine Paschen $α$ intensities, and derive near-infrared spectral energy distributions (SEDs). From these diagnostics we define a typology of ONC disks. Type I sources show merged IFs and DFs close to the disk surface. Type II sources have DFs at the disk surface and IFs located tens of astronomical units away. Type III sources show a DF at the disk surface but no IF. For all types, PAH emission traces the PDR. We find that the disk radius $r_{\rm disk}$ increases with projected distance to the ionizing source $d_{\rm proj}$, following $r_{\rm disk} \propto d_{\rm proj}^{0.30}$, consistent with disk truncation by photoevaporation. Disk radii measured in the infrared are larger than those measured at millimeter wavelengths, suggesting radial dust segregation within the disks. In agreement with PDR models, the thermal pressure in the disk PDR increases with the FUV radiation field $G_0$, but with a flatter slope. Finally, the SEDs of candidate Jupiter Mass Binary Objects (JuMBOs) are similar to those of Type III disks, except for JuMBO24, which resembles a Type I or Type II source. Its SED is consistent with a young low-mass binary hosting an unresolved ionized disk.

Figures (21)

• Figure 1: Composite color Hubble Space Telescope view of the Orion Nebula as provided by robberto_2013_HST. The field of view (FOV) of the NIRCam images from GTO program 1256 is shown as the cyan dotted box. Both FOVs from the PDRs4All NIRCam images are shown as the continuous boxes, and the parallel field of views are shown with dashed boxes for each of the filters listed in Table \ref{['tab:filters']}.
• Figure 2: NIRCam images of the disks seen in silhouette in the narrowband filters from the PDRs4All program dataset. The color scale is in $\log (\rm W\:m^{-2}$ µ m$^{-1}$ sr$^{-1})$.
• Figure 3: [Feii], Paschen $\alpha$, H$_2$ 1-0 S(1) and PAH emission maps of a subsample of ONC protoplanetary disks, obtained following Equation \ref{['eq:recipes_lines']}. The images are north-aligned and in units of $\rm W\ m^{-2}\ sr^{-1}$.
• Figure 4: (A): HST-image of 165-235 in the H$\alpha$ F658N filter at 0.658 µm. (B) JWST-image in the Pa $\alpha$ F187N filter at 1.87 µm. (C): In red, contours of 165-235 from the HST image. In blue, contours from the JWST image.
• Figure 5: Schematic overview of the observational categories for ONC disks. Type I, the IF (Pa $\alpha$ emitting layer, in blue) is close to the disk's surface and almost merged with the DF (H$_2$ emitting layer, in yellow). Type II, the IF is placed further away from the disk's surface and DF. In these two first categories, the disk is in the Hii region and embedded in a photoevaporative wind (PAH emitting area) surrounded by a bright IF. Type III, the disk does not have any associated IF, but still has a DF. This corresponds to the case where the disk is FUV irradiated only, beyond the Strömgren's sphere produced by the Trapezium.