PDRs4All XIII. Empirical prescriptions for the interpretation of JWST imaging observations of star-forming regions

TL;DR

This paper develops empirical methods to interpret JWST infrared images of star-forming regions by linking observed emissions to physical conditions, aiding both Galactic and extragalactic studies.

Contribution

It provides new empirical prescriptions to derive emission line and PAH intensities from JWST imaging data, calibrated with detailed spectroscopic observations of the Orion Bar PDR.

Findings

Accurate predictions for Pa-α, Br-α, and PAH features using the prescriptions.

Identification of environmental dependencies for FeII, H2, and other emissions.

Linear combinations of images effectively trace different gas components.

Abstract

(Abridged) JWST continues to deliver incredibly detailed infrared (IR) images of star forming regions in the Milky Way and beyond. IR emission from star-forming regions is very spectrally rich due to emission from gas-phase atoms, ions, and polycyclic aromatic hydrocarbons (PAHs). Physically interpreting IR images of these regions relies on assumptions about the underlying spectral energy distribution in the imaging bandpasses. We aim to provide empirical prescriptions linking line, PAH, and continuum intensities from JWST images, to facilitate the interpretation of JWST images in a wide variety of contexts. We use JWST PDRs4All Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) imaging and Near-Infrared Spectrograph (NIRSpec) integral field unit (IFU) and MIRI Medium Resolution Spectrograph (MRS) spectroscopic observations of the Orion Bar photodissociation region (PDR), to directly compare and cross-calibrate imaging and IFU data at ~100 AU resolution over a region where the radiation field and ISM environment evolves from the hot ionized gas to the cold molecular gas. We measure the relative contributions of line, PAH, and continuum emission to the NIRCam and MIRI filters as functions of local physical conditions. We provide empirical prescriptions based on NIRCam and MIRI images to derive intensities of emission lines and PAH features. Within the range of the environments probed in this study, these prescriptions accurately predict Pa-$\alpha$, Br-$\alpha$, PAH 3.3 $\mu$m and 11.2 $\mu$m intensities, while those for FeII 1.644 $\mu$m, H$_2$ 1--0 S(1) 2.12 $\mu$m and 1--0 S(9) 4.96 $\mu$m, and PAH 7.7 $\mu$m show more complicated environmental dependencies. Linear combinations of JWST NIRCam and MIRI images provide effective tracers of ionized gas, H$_2$, and PAH emission in PDRs. We expect these recipes to be useful for both the Galactic and extragalactic communities.