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

We present JWST /NIRSpec IFU observations of the z = 7 . 152 galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system (log(10)(M */M-o) = 9 . 8 +/- 0 . 2 ) is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our data set contains detections of [Oii]lambda lambda 3726,3729, [Ne iii]lambda lambda 3869, 3968 , Balmer lines, [O iii]lambda lambda 4959, 5007 , He i lambda 5875, and weak [O iii]lambda 4363. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e. electron temperature, Te, electron density, ne, and colour excess, E(B-V ) ). The resulting line fluxes are used to constrain the gas-phase metallicity (Z(g) 0 . 2-0.3 solar) and H 3-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 z > 5 . 5 . Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM < 400 km s(-1)) and broad (FWHM > 500 km s-1) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C ii]158 & micro;m and [Oiii]88 & micro; 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 z > 4 , but show contrasting properties (e.g. M (*), Z(g)), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA data sets, our analysis opens new windows into the merging system B14-65666.