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
Abstract
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.
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Authors: Abdurrouf, Massimo Ricotti
Institutions: Northwestern University, Johns Hopkins University, Tufts University, University of Manchester, University of Toronto, Consejo Superior de Investigaciones Científicas, University of Copenhagen, The University of Tokyo, The University of Texas at Austin, University of Geneva, Centre National de la Recherche Scientifique, University of Maryland, College Park, Arizona State University, Ben-Gurion University of the Negev, University of Ljubljana, Stockholm University, University of California System, Oklahoma State University, Instituto de Física de Cantabria, Indiana University, California Institute of Technology, National Research Council Canada, Chiba University, Instituto de Astrofísica de Andalucía, National Institute for Astrophysics, Wellesley College, Osservatorio di Astrofisica e Scienza dello Spazio, Space Telescope Science Institute, Center for Astrophysics Harvard & Smithsonian, Herzberg Institute of Astrophysics, International Space Science Institute, Université de Lyon, Association of Universities for Research in Astronomy