Spatially Resolved Physical Properties of Young Star Clusters and Star-forming Clumps in the Brightest z > 6 Galaxy, the Strongly Lensed Cosmic Spear at z = 6.2
Year: 2026
Type: article
Abstract: We present a spatially resolved analysis of stellar populations in the brightest z > 6 galaxy known to date (AB mag 23), the strongly lensed MACS0308−zD1 (dubbed the “Cosmic Spear”) at z spec = 6.2. New JWST NIRCam imaging and high-resolution NIRSpec integral field unit (IFU) spectroscopy span the rest-frame ultraviolet to optical. The NIRCam imaging reveals bright star-forming clumps and a tail consisting of three distinct, extremely compact star clusters that are multiply imaged by gravitational lensing. The star clusters have delensed effective radii of R eff ≲ 8 pc, stellar masses of M * ∼ 10 6 –10 7 M ⊙ , and high stellar mass surface densities of Σ * ≳ 2 × 10 4 M ⊙ pc −2 . While their stellar populations are very young (∼6–11 Myr), their dynamical ages exceed unity, consistent with the clusters being gravitationally bound systems. Placing the star clusters in the size versus stellar mass density plane, we find they occupy a region similar to other high-redshift star clusters within galaxies observed recently with JWST, being significantly more massive and denser than local star clusters. Spatially resolved analysis of the brightest clump reveals a compact, intensely star-forming core. The ionizing photon production efficiency ( ξ ion ) is slightly suppressed in this central region, potentially indicating a locally elevated Lyman continuum escape fraction facilitated by feedback-driven channels.
Source: The Astrophysical Journal
Authors: Abdurro’uf, Dan Coe, Tom Resseguier, Calla Murphy, Xinfeng Xu, Angela Adamo, Namrata Roy, Alaina Henry, Vasily Kokorev, Gabriel Brammer, Seiji Fujimoto, Henry C. Ferguson, Amanda Pagul, Rogier A. Windhorst, Timothy Heckman, Jose M. Diego, Hollis B. Akins, Joseph F. V. Allingham, Ricardo O. Amorín, Danielle A. Berg, Maruša Bradač, Larry D. Bradley, Wenlei Chen, John Chisholm, Christopher J. Conselice, Pratika Dayal, Miroslava Dessauges-Zavadsky, Andreas L. Faisst, Steven L. Finkelstein, Yoshinobu Fudamoto, Lukas J. Furtak, Yuichi Harikane, Tiger Yu-Yang Hsiao, Yolanda Jimenez-Teja, Anton M. Koekemoer, Rebecca L. Larson, Ray A. Lucas, Matteo Messa, Lamiya Mowla, Minami Nakane, Gaël Noirot, Richard Pan, Massimo Pascale, Johan Richard, Massimo Ricotti, Luke Robbins, Daniel Schaerer, Fengwu Sun, Eros Vanzella, Brian Welch, Chris Willott, Adi Zitrin
Institutions: Space Telescope Science Institute, Johns Hopkins University, Indiana University, Association of Universities for Research in Astronomy, Northwestern University, Stockholm University, Arizona State University, The University of Texas at Austin, University of Copenhagen, Consejo Superior de Investigaciones Científicas, Instituto de Física de Cantabria, Ben-Gurion University of the Negev, Instituto de Astrofísica de Andalucía, University of Ljubljana, Oklahoma State University, University of Manchester, University of Toronto, University of Geneva, California Institute of Technology, Chiba University, The University of Tokyo, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics, Wellesley College, Tufts University, University of California System, Université de Lyon, University of Maryland, College Park, Centre National de la Recherche Scientifique, Center for Astrophysics Harvard & Smithsonian, International Space Science Institute, Herzberg Institute of Astrophysics, National Research Council Canada
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7114777520