The Astrophysical Journal· 2026Q1
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
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- Q1SCImago
- 2026year
Short summary
JWST NIRCam imaging reveals three extremely compact star clusters (R_eff ≲ 8 pc, M* ~ 10^6–10^7 M☉) in the z=6.2 galaxy MACS0308−zD1, exhibiting higher mass surface densities (Σ* ≳ 2 × 10^4 M☉ pc⁻²) than local clusters.
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Key points
- Resolved three multiply imaged, extremely compact star clusters in the z=6.2 galaxy MACS0308−zD1.
- Star clusters have delensed effective radii of ≲ 8 pc and stellar masses of 10^6–10^7 M☉.
- Observed high stellar mass surface densities (Σ* ≳ 2 × 10^4 M☉ pc⁻²) for these early universe clusters.
- These clusters are significantly more massive and denser than local star clusters.
- A bright star-forming clump shows suppressed ionizing photon production efficiency in its core.
AI-generated from the title and abstract; the full text is not read.
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.
The authors' abstract, as published at the source. The Astrophysical Journal, 2026 · DOI ↗
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Field: Astronomy and Astrophysics
Astronomy and AstrophysicsPhysics and Astronomy