A JWST NIRCam/MIRI view of the W51A high-mass star-forming region

We present observations of the W51A region, including the massive protoclusters W51-E and W51-IRS2, with JWST in 10 NIRCam and 5 MIRI filters. In this work, we highlight the most novel features apparent in these images and compare them with other multi-wavelength images. The broad view of the NIRCam/MIRI images of the W51A region shows that areas dominated by warm dust and ionized gas are distinct from those dominated by PAHs. The high angular resolution of the JWST images resolves dust filaments in high contrast, revealing geometrically converging features feeding W51-E and a cavity around W51-IRS2. This picture adds support to the hypothesis that feedback from W51-IRS2 is suppressing further gas infall onto the protocluster, while by contrast, gas is still accreting onto W51-E. Comparing the NIRCam and MIRI images to ALMA data, we find 24 sources detected by both JWST and ALMA, accounting for only $\sim10%$ of the ALMA sources; the rest are too embedded or too cool to be detected by JWST. A knot of [Fe II] and H$_2$ emission north of W51-IRS2, previously detected in ground-based images, reveals peculiarly bright and compact peaks detected in all JWST bands. The knot is likely the most energetic example of a protostellar jet driven by a massive star impacting dense interstellar medium. The new images provide a complementary view to the previous long-wavelength perspective on this 4 x 8 pc area of one of the most active star-forming regions in our Galaxy, revealing new mysteries to be further explored.

💡 Research Summary

This paper presents the first JWST NIRCam and MIRI imaging of the massive star‑forming complex W51A, covering a 4 × 8 pc area that includes the two protoclusters W51‑E (also known as W51 Main) and W51‑IRS2. Observations were carried out in ten NIRCam filters (1.4–4.8 µm) and five MIRI filters (5.6–21 µm) with total exposure times of 1890 s and 56 s respectively. The data were reduced with the standard JWST pipeline (v1.17.1) with custom handling of saturated pixels and 1/f noise removal.

The authors use color‑difference images to separate three key components: warm dust (traced by F480M–F360M, T ≈ 500 K), ionized gas (Br α line in F405N vs. continuum F410M), and polycyclic aromatic hydrocarbons (PAHs, traced by the F335M/F480M ratio). The maps show that ionized gas and warm dust coexist in H II regions, while PAH emission is strongly suppressed inside the ionized zones and enhanced at the surrounding photodissociation region (PDR) boundaries, reproducing the classic PAH‑destruction pattern seen in other Galactic H II regions.

High‑resolution NIRCam images reveal a network of dark, filamentary dust lanes that converge toward the center of W51‑E, suggesting ongoing accretion of material onto this protocluster. In contrast, the interior of W51‑IRS2 is largely cleared of such filaments, displaying a cavity that the authors attribute to strong radiative and mechanical feedback from the massive stars within the cluster. This visual contrast supports the hypothesis that feedback from IRS2 is inhibiting further gas inflow, whereas W51‑E remains in a growth phase.

Cross‑matching with the ALMA 1.3 mm compact source catalog (≈200 “PPOs”) finds only 24 common objects, roughly 10 % of the ALMA detections. The majority of ALMA sources are either too deeply embedded or too cool to be seen in the near‑ and mid‑infrared, highlighting the complementary nature of JWST and (sub)mm observations.

A particularly striking feature is a compact knot of