GA-NIFS: interstellar medium properties and tidal interactions in the evolved massive merging system B14-65666 at z = 7.152

Journal article

We present JWST/NIRSpec IFU observations of the galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system () is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our data set contains detections of [O ii], [Ne iii], Balmer lines, [O iii], He i, and weak [O iii]. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e. electron temperature, , electron density, , and colour excess, ). The resulting line fluxes are used to constrain the gas-phase metallicity ( solar) and H-based star formation rate for each region. Common line ratio diagrams (O32–R23, R3–R2, Ne3O2–R23) reveal that each line-emitting region lies at the intersection of low- and high-redshift galaxies, suggesting low ionization and higher metallicity compared to the predominantly lower-mass galaxies studied with the JWST/NIRSpec IFU so far at . Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM km s) and broad (FWHM km s) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C ii]158m and [O iii]88 m data shows a similar velocity structure, and we explore optical-far infrared diagnostics. The two core galaxies both lie on the mass-metallicity relation at , but show contrasting properties (e.g. , ), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA data sets, our analysis opens new windows into the merging system B14-65666.

Authors: Jones, GC; Bowler, RAA; Bunker, AJ; Curti, M; Arribas, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 547
• Issue: 2
• Pages: stag336
• Article number: stag336
• Publication date: 2026-02-17
• Acceptance date: 2026-02-15
• DOI: 10.1093/mnras/stag336
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: galaxies: high-redshift; galaxies: kinematics and dynamics; galaxies: ISM; galaxies: interactions