Galaxies are arranged across a vast “cosmic web” of filaments, walls, and nodes. Galaxy clusters, the most massive structures in the Universe, host hundreds to thousands of galaxies and lie at the intersections of this web. They are dominated by old, quiescent galaxies whose stars formed over 10 billion years ago, during the so-called “cosmic noon”, the most intensely active period of star formation and black hole activity in the Universe. At this stage, galaxy clusters in formation are referred to as protoclusters, and simulations predict them to be sites of short-lived but strong starbursts fueling rapid galaxy growth. How galaxies evolve in dense environments remains one of the key open questions, crucial to understanding the formation of massive galaxies and the emergence of large-scale structure in the Universe.
The JADES project tackled this challenge by studying how galaxies assembled their mass within one of the most massive and best-known protoclusters at cosmic noon: the Spiderweb. A major challenge is that vigorous star formation is heavily obscured by dust, making it difficult to trace with optical telescopes. To address this, JADES combined high-resolution near-infrared (NIR) imaging from the James Webb Space Telescope (JWST/NIRCam) with deep data from the Atacama Large Millimeter Array (ALMA), making the Spiderweb the first protocluster ever observed with this unparalleled combination of instruments. JWST’s broad and narrow-band filters capture the near-infrared Paschen-β (Paβ) emission line, a dust-penetrating tracer of star formation, while ALMA maps the cold dust and gas that fuel these episodes. To represent this joint effort between JWST, ALMA, and the Spiderweb field, the project also created a dedicated logo (Fig. 1). Together with ground-based observations, this multiwavelength approach yielded the first panoramic, high-resolution study of both obscured and unobscured star formation across a protocluster. JADES focused on three main scientific goals:
1. Map star formation activity across the Spiderweb protocluster using JWST/NIRCam Paβ narrow-band imaging. This revealed both known star-forming galaxies and previously undetected optically dark Paβ-emitting members hidden by dust.
2. Trace the spatial distribution of dusty star-forming galaxies by comparing the NIR Paβ emission (JWST) with the optical H-alpha (Hα) line from Subaru/MOIRCS. The ratio between these tracers examines how dust attenuation varies across the protocluster, shedding light on how environmental interactions shape galaxy growth.
3. Measure the dust and molecular gas reservoirs fueling star formation by combining JWST imaging with ALMA dust continuum and CO(1–0) observations from the Australia Telescope Compact Array (ATCA). This allowed us to quantify the available gas, estimate how long star formation can continue, and map the distribution of stars, gas, and dust within galaxies, crucial for understanding their transformation into passive ellipticals.
By delivering the first comprehensive view of star formation and gas content in a forming galaxy cluster at cosmic noon, JADES sets a new benchmark for understanding environmental effects on galaxy evolution at this cosmic epoch.
