X-shooter NIR spectrum of the HZ10 galaxy. Top panel: combined, rebinned (≈ 85 km s⁻¹), and smoothed (1.1 nm × 0.12″) 2D spectrum. The C III] λλ1907, 1909 line is detected in the center of the slit with the negative flux on each side. The bottom three panels illustrate the extracted 1D spectra rebinned by ≈ 210 km s⁻¹, ≈ 170 km s⁻¹, and ≈ 140 km s⁻¹, respectively. Shaded blue regions indicate the flux, dotted lines indicate the uncertainties, whereas orange solid line is the best Gaussian fit. Expected positions of the [C III] λ1907 at λ = 1269.7 nm and [C III] λ1909 line at λ = 1271.0 nm, based on the Lyα spectroscopic redshift, are shown as yellow and red lines, respectively.