JWST spectroscopic confirmation of the Cosmic Gems arc at z = 9.625 : insights into the small-scale structure of a post-burst system

Messa, Matteo (avtor), Bradač, Maruša (avtor)

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 ▫$R \simeq 30-300$▫ covering the spectral range ▫$0.8-5.3\ \mu$▫m, covering the spectral range ▫$0.8-5.3$▫ reveals a pronounced Ly▫$\alpha$▫-continuum break at ▫$\lambda \simeq 1.3\ \mu$▫m, as well as weak optical H▫$\beta$▫ and [O III] ▫$\lambda4959$▫ emission lines at ▫$z = 9.625 \pm 0.002$▫, located in the reddest part of the spectrum (▫$\lambda>5.1\ \mu$▫m). No additional ultraviolet or optical emission lines are reliably detected. A weak Balmer break is measured alongside a very blue ultraviolet slope (▫$\beta \leq -2.5, \text{F}_{\lambda} \sim \lambda^{\beta}$▫). 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 (▫$\Sigma_{M_{\ast}} = 10^5-10^6\ M_{\odot}$▫). Additionally, four compact stellar systems consistent with star clusters (▫$\lesssim$▫10 pc) are identified along the extended tail of the arc. A sub-parsec line-emitting H II region straddling the critical line, lacking a NIRCam counterpart, is also serendipitously detected. The Cosmic Gems arc thus offers a rare opportunity to investigate, at parsec scales, the aftermath of a star formation burst in the early Universe.

• Jezik: Angleški jezik
• Ključne besede: galaxies, gravitational lensing, redshift, star clusters, star formation
• Vrsta gradiva: Članek v reviji
• Tipologija: 1.01 - Izvirni znanstveni članek
• Organizacija: FMF - Fakulteta za matematiko in fiziko
• Status publikacije: Objavljeno
• Različica publikacije: Objavljena publikacija
• Leto izida: 2026
• Št. strani: 21 str.
• Številčenje: Vol. 705, art. no. A173
• PID: 20.500.12556/RUL-181940
• UDK: 524.8
• ISSN pri članku: 1432-0746
• DOI: 10.1051/0004-6361/202556574
• COBISS.SI-ID: 275650051
• Datum objave v RUL: 20.04.2026

Gradivo je del revije

• Naslov: Astronomy & astrophysics
• Skrajšan naslov: Astron. astrophys.
• Založnik: EDP Sciences
• ISSN: 1432-0746
• COBISS.SI-ID: 392577

Licence

• Licenca: CC BY 4.0, Creative Commons Priznanje avtorstva 4.0 Mednarodna
• Povezava: http://creativecommons.org/licenses/by/4.0/deed.sl
• Opis: To je standardna licenca Creative Commons, ki daje uporabnikom največ možnosti za nadaljnjo uporabo dela, pri čemer morajo navesti avtorja.

Sekundarni jezik

• Jezik: Slovenski jezik
• Ključne besede: galaksije, gravitacijsko lečenje, rdeči premik, zvezdne kopice, nastanek zvezd

Projekti

• Financer: ARIS - Javna agencija za znanstvenoraziskovalno in inovacijsko dejavnost Republike Slovenije
• Številka projekta: N1-0238
• Naslov: Raziskave kozmične zore z James Webb vesoljskim teleskopom