Periodic Reporting for period 1 - JADES (JWST + ALMA Dust Enshrouded Star-formation in the Spiderweb protocluster at the cosmic noon)
Reporting period: 2023-06-01 to 2025-05-31
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.
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.
Scientifically, our JWST/NIRCam program yielded the first Paβ luminosity function in a protocluster and identified new dust-enshrouded galaxies missed in previous surveys. We derived Paβ/Hα ratios to trace dust attenuation and its dependence on local density and cluster-centric distance. To examine star formation fueling mechanisms, we incorporated ALMA Band-6 dust continuum and molecular gas observations from ATCA, enabling estimates of dust masses, gas fractions, and depletion timescales. These results revealed both short-lived starbursts and gas-fed sustained star formation, offering insight into the environmental drivers of galaxy evolution in the Spiderweb.
JADES has been highly productive, with 12 peer-reviewed articles submitted to top-tier journals (A&A, ApJ, MNRAS), 9 already accepted, including two as first author. Four form the scientific core of the project and are the focus of this summary. Notably, two were featured in an ESA press release (“Webb finds surprises in Spiderweb protocluster field,” Dec 4, 2024; Fig. 2) and a related release by the Instituto de Astrofísica de Canarias (IAC). The results also received coverage in international newspapers and the German magazine Sterne und Weltraum, underscoring their scientific and public impact. I presented these findings at six international conferences, including four invited talks. A major highlight was the conference “From Fake News to Real Clusters”, which I chaired and organized in May 2025 at the IAC, bringing together 30 early-career and senior researchers from eight countries and three continents, boosting JADES' visibility and fostering future collaborations.
JADES has been highly productive, with 12 peer-reviewed articles submitted to top-tier journals (A&A, ApJ, MNRAS), 9 already accepted, including two as first author. Four form the scientific core of the project and are the focus of this summary. Notably, two were featured in an ESA press release (“Webb finds surprises in Spiderweb protocluster field,” Dec 4, 2024; Fig. 2) and a related release by the Instituto de Astrofísica de Canarias (IAC). The results also received coverage in international newspapers and the German magazine Sterne und Weltraum, underscoring their scientific and public impact. I presented these findings at six international conferences, including four invited talks. A major highlight was the conference “From Fake News to Real Clusters”, which I chaired and organized in May 2025 at the IAC, bringing together 30 early-career and senior researchers from eight countries and three continents, boosting JADES' visibility and fostering future collaborations.
By combining high-resolution NIR imaging from JWST with deep (sub)millimeter observations from ALMA and ATCA, we have delivered the most complete multi-tracer view to date of a cosmic noon protocluster to date. Our core scientific results include:
1. First dual-tracer (Paβ and Hα) map of star formation in a protocluster. JADES identified 41 Paβ emitters, including many optically dark, dusty galaxies missed by Hα surveys, enabling an extinction-insensitive view of the star-forming population. Fig. 3 shows their spatial distribution (left) and examples of dual Hα + Paβ emitters observed by Subaru and JWST.
2. Dust attenuation across the protocluster. Using Paβ/Hα ratios from 43 spectroscopically confirmed members, JADES delivered the first extinction map of a protocluster, showing moderate dust obscuration and no clear environmental imprints, suggesting secular star formation dominates over interaction-driven modes at this stage.
3. Molecular gas reservoir census with ATCA. This revealed a stellar mass threshold separating gas-rich, low-mass galaxies likely fed by cosmic filaments from more evolved, gas-depleted systems. The high prevalence of AGN in massive galaxies suggests that feedback, together with environmental effects, drives gas depletion and quenching, in line with the emergence of the red sequence in clusters.
4. Complete survey of ALMA-bright dusty star-forming galaxies (DSFGs) in the Spiderweb field. We detected 47 dust continuum sources, revealing a factor-of-two overdensity relative to blank fields, with even stronger concentrations in substructures such as infalling groups. In addition, direct comparison between ALMA and JWST emission revealed the presence of extended stellar disks within them, supporting the scenario of gas-fed secular growth for these sources instead of violent gravitational interactions.
In summary, JADES has established a new standard for early protocluster observational studies. To build on this progress, several future key actions are needed: 1) spectroscopic confirmation of Paβ-only sources to refine membership and completeness; 2) high-resolution CO kinematics to distinguish between merger-driven and secular evolution; 3) statistical protocluster surveys to assess whether the Spiderweb is representative or exceptional; and 4) systematic comparisons with cosmological simulations. These steps will ensure that the legacy of JADES continues to shape our understanding of galaxy evolution in the cosmic web.
1. First dual-tracer (Paβ and Hα) map of star formation in a protocluster. JADES identified 41 Paβ emitters, including many optically dark, dusty galaxies missed by Hα surveys, enabling an extinction-insensitive view of the star-forming population. Fig. 3 shows their spatial distribution (left) and examples of dual Hα + Paβ emitters observed by Subaru and JWST.
2. Dust attenuation across the protocluster. Using Paβ/Hα ratios from 43 spectroscopically confirmed members, JADES delivered the first extinction map of a protocluster, showing moderate dust obscuration and no clear environmental imprints, suggesting secular star formation dominates over interaction-driven modes at this stage.
3. Molecular gas reservoir census with ATCA. This revealed a stellar mass threshold separating gas-rich, low-mass galaxies likely fed by cosmic filaments from more evolved, gas-depleted systems. The high prevalence of AGN in massive galaxies suggests that feedback, together with environmental effects, drives gas depletion and quenching, in line with the emergence of the red sequence in clusters.
4. Complete survey of ALMA-bright dusty star-forming galaxies (DSFGs) in the Spiderweb field. We detected 47 dust continuum sources, revealing a factor-of-two overdensity relative to blank fields, with even stronger concentrations in substructures such as infalling groups. In addition, direct comparison between ALMA and JWST emission revealed the presence of extended stellar disks within them, supporting the scenario of gas-fed secular growth for these sources instead of violent gravitational interactions.
In summary, JADES has established a new standard for early protocluster observational studies. To build on this progress, several future key actions are needed: 1) spectroscopic confirmation of Paβ-only sources to refine membership and completeness; 2) high-resolution CO kinematics to distinguish between merger-driven and secular evolution; 3) statistical protocluster surveys to assess whether the Spiderweb is representative or exceptional; and 4) systematic comparisons with cosmological simulations. These steps will ensure that the legacy of JADES continues to shape our understanding of galaxy evolution in the cosmic web.