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

Abstract

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 (log10(M*/M⊙)=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 [O ii]λλ3726,3729, [Ne iii]λλ3869,3968, Balmer lines, [O iii]λλ4959,5007, He iλ5875, and weak [O iii]λ4363. 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 (Zg ~ 0.2-0.3 solar) and Hβ-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]158μm and [O iii]88μm 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*, Zg), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA data sets, our analysis opens new windows into the merging system B14-65666.