LAUSR

We present observations of the $z$ ∼ 5.7 Lyman-break galaxy HZ10 with the JWST/NIRSpec IFU in high and low spectral resolution (G395H, spectral resolving power R ∼ 2700 and PRISM, R ∼ 100, respectively), as part of the GA-NIFS program. By spatially resolving the source (spatial resolution ∼0.15″ or ∼0.9 kpc), we find three spatially and spectrally distinct regions of line emission along with one region of strong continuum emission, all within a projected distance of <10 kpc. The R2700 data features strong detections in Hβ, [O iii] λλ4959, 5007, [N ii] λλ6548, 6584, Hα, and [S ii] λλ6716, 6731. The R100 data additionally contains a strong detection of the Lyα break, rest-frame UV and optical continuum, and [O ii] λλ3726, 3729. None of the detected lines present strong evidence for AGN excitation from line diagnostic diagrams, and no high-ionisation lines are detected. Using the detected lines, we constrain the electron density $\left( \rm \log _{10}\left( n_e / cm^{-3}\right)\sim 3\right)$ and metallicity (∼0.5 − 0.7 solar) in each component. Spaxel-by-spaxel fits reveal a strong east-west velocity gradient and significant line asymmetries (possibly indicating tidal features or outflows). The western component features a very red UV slope (βUV ∼ −0.9) and significant Hα emission, suggesting an evolved population and active star formation. A comparison to high resolution (∼0.3″ or ∼1.8 kpc) [${\rm C\, \small {II}}$]  158 μm imaging obtained with the Atacama Large Millimetre/submillimetre Array (ALMA) reveals areas of dust obscuration. Altogether, these data suggest that HZ10 represents an ongoing merger, with a complex distribution of stars, gas, and dust <1 Gyr after the Big Bang.