Star formation and AGN diagnostics. The top left panel shows the G140M spectrum of CEERS-1019 (in black and 1σ uncertainty in grey) around the expected positions of N Vλλ1238, 1242 (marked with vertical lines), which are not detected (1.44 × 10⁻¹⁸ erg s⁻¹ cm⁻² at 3σ). Lyα emission is also marked. The top middle and right panels show the best fits (green) to the Hβ emission line using dual-component (middle, narrow and broad components in blue and red, respectively) and single-component (right) Gaussian profiles. The bottom panels show star formation (blue) and AGN (red) photoionization models using several rest-frame UV lines. The position of CEERS-1019 (dark blue circle) aligns with the predictions of star-forming models in all diagnostic diagrams. The location of other known star-forming galaxies with strong nitrogen emission, GN-z11 (Bunker et al. 2023), the Lynx arc (Villar-Martín et al. 2004), SMACS2031 (Patrício et al. 2016), and Mrk 996 (Mingozzi et al. 2022) are also marked with different symbols as indicated in the legend.