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*/Msol)=9.8+/-0.2) is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our dataset contains detections of [OII]3726,3729, [NeIII]3869,3968, Balmer lines, [OIII]4959,5007, HeI5875, and weak [OIII]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 (Zg~0.2-0.3 solar) and HBeta-based SFR 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 ionisation 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 [CII]158um and [OIII]88um 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 datasets, our analysis opens new windows into the merging system B14-65666.

Figures (14)

• Figure 1: Spectra extracted from our JWST/NIRSpec IFU data cube using the two primary apertures (E and W, see Table \ref{['aper_table']}). Aperture loss corrections (see Appendix \ref{['psfapp']}) have been applied to each spectrum. We zoom in around each emission line and present the observed spectrum, the best-fit model, and its narrow and broad components. The residual is included in the lower panel. The redshifted wavelengths of each fit line (using the best-fit redshift of the narrow component) are marked with vertical dashed lines.
• Figure 2: Integrated total fluxes of emission lines, as derived through spaxel-by-spaxel fit. Only $>3\sigma$ fluxes are shown. Each panel displays a field of view of $2.2"\times2.2"$ centred on 10h01m40.69s +1$^{\circ}$54$'$52.55$"$. A physical scale bar of 2 kpc scale bar is included in each panel.
• Figure 3: Line of sight velocity maps, as derived through spaxel-by-spaxel fits. The top row includes maps of $v_{50}$ (i.e., the velocity at which each line reaches $50\%$ of its total flux) for [OIII]$\lambda5007$, [C II]158$\mu$m, and [O III]88$\mu$m. Maps of $v_{50}$ for the narrow and broad component of [OIII]$\lambda5007$ are shown in the first two panels of the lower row. The bottom right panel presents the best-fit asymmetry of [OIII]$\lambda5007$ (see Section \ref{['nmapc']} for definition). Each panel displays a field of view of $2.2"\times2.2"$ centred on 10h01m40.69s +1$^{\circ}$54$'$52.55$"$. A physical scale bar of 2 kpc scale bar is included in each panel. For each, we show the PSF as a red ellipse to the lower left. North is up and east is to the left.
• Figure 4: Maps of $w_{80}$ (i.e., the difference in velocity between the points at which each line reaches $10\%$ and $90\%$ of its total flux), as derived through spaxel-by-spaxel fits for [OIII]$\lambda5007$, [C II]158$\mu$m, and [O III]88$\mu$m. Maps of $w_{80}$ for the narrow and broad component of [OIII]$\lambda5007$ are shown in the lower row. Each panel displays a field of view of $2.2"\times2.2"$ centred on 10h01m40.69s +1$^{\circ}$54$'$52.55$"$. A physical scale bar of 2 kpc scale bar is included in each panel. For each, we show the PSF as a red ellipse to the lower left. North is up and east is to the left.
• Figure 5: Line ratio diagnostics, as derived through spaxel-by-spaxel fit. Each panel displays a field of view of $2.2"\times2.2"$ centred on 10h01m40.69s +1$^{\circ}$54$'$52.55$"$. A physical scale bar of 2 kpc scale bar is included in each panel. For each, we show the PSF as a red ellipse to the lower left. North is up and east is to the left.