JWST spectroscopic confirmation of the Cosmic Gems arc at z = 9.625

作者：Matteo Messa, E. Vanzella, F. Loiacono, A. Adamo, Masamune Oguri, Keren Sharon, Larry Bradley, L. Christensen, Adélaïde Claeyssens, J. Richard, Abdurro'uf Abdurro'uf, F. E. Bauer, P. Bergamini, A. Bolamperti, Maruša Bradač, F. Calura, Dan Coe, J. M. Diego, C. Grillo, Tiger Yu-Yang Hsiao, Akio Inoue, S. Fujimoto, M. Lombardi, M. Meneghetti, Tom Resseguier, Massimo Ricotti, P. Rosati, Brian Welch, Rogier A. Windhorst, Xinfeng Xu, Erik Zackrisson, Anita Zanella, Adi Zitrin · 发表于：Astronomy and Astrophysics · 年份：2025 · DOI：10.1051/0004-6361/202556574 · 被引用次数：9 · 研究领域：Galaxies: Formation, Evolution, Phenomena、Astrophysics and Star Formation Studies、Astronomy and Astrophysical Research

We present JWST/NIRSpec integral field spectroscopy of the Cosmic Gems arc, strongly magnified by the galaxy cluster SPT-CL J0615−5746. Six-hour integration using NIRSpec prism spectroscopy (resolution R ≃ 30 − 300), covering the spectral range 0.8 − 5.3 μm, reveals a pronounced Ly α -continuum break at λ ≃ 1.3 μm, as well as weak optical H β and [O III ] λ 4959 emission lines at z = 9.625 ± 0.002, located in the reddest part of the spectrum ( λ > 5.1 μm). No additional ultraviolet or optical emission lines are reliably detected. A weak Balmer break is measured alongside a very blue ultraviolet slope ( β ≤ −2.5, F λ ∼ λ β ). Spectral fitting with Bagpipes suggests that the Cosmic Gems galaxy is in a post-starburst phase, making it the highest-redshift system currently observed in a mini-quenched state. Spatially resolved spectroscopy at tens of parsecs shows relatively uniform features across subcomponents of the arc. These findings align well with the physical properties previously derived from JWST/NIRCam photometry of the stellar clusters, now corroborated by spectroscopic evidence. In particular, five observed star clusters exhibit ages of 7 − 30 Myr. An updated lens model constrains the intrinsic sizes and masses of these clusters, confirming they are extremely compact and denser than typical star clusters in local star-forming galaxies (Σ M ★ = 10 5 − 10 6 M ⊙ ). Additionally, four compact stellar systems consistent with star clusters (≲10 pc) are identified along th...