2025MNRAS.544.4025L

Gas-phase oxygen abundance (metallicity) properties can be constrained through emission line analyses, and are of great importance to investigate galaxy evolution histories. We present an analysis of the integrated and spatially resolved rest-frame optical emission line properties of the ionized gas in 43 star-forming galaxies at $z\sim 1.5$ in the K-band Multi Object Spectrograph Ultra-deep Rotational Velocity Survey. Using the [N II]$\lambda 6584$/H $\alpha$ (N₂), ([O II]$\lambda \lambda 3727,9+$[O III]$\lambda \lambda 4959,5007$)/H $\beta$ (R23), and for the first time [N II]$\lambda 6584$/[O II]$\lambda \lambda 3727,9$ (N₂O₂) indicators at this redshift, we measure the gas-phase metallicities and their radial gradients. On $\sim 4$-kpc scales metallicity gradients measured from N₂O₂ and those measured from N₂ are in good agreement when considering the spatial distributions of dust in each galaxy, as parametrized by dust attenuation radial gradients. We report a nearly flat metallicity gradient distribution typically at $z\sim 1.5$, with the 50th, 16th, and 84th percentiles at 0.01, $-0.03$, and 0.05 dex kpc$^{-1}$, respectively. The findings agree well with previous observational studies and simulations at this epoch. We ascribe the observed negative metallicity gradients to a natural result from self-regulating systems, and the positive ones to potential galactic fountains and higher merger rates.