NISER-IUCAA New Simulations of JWST GAlaxies and Quasars(NINJA): Properties of galaxies at $5 \leq z \leq 10$

We present the NINJA suite of cosmological hydrodynamical simulations developed to investigate galaxy formation and evolution at $z \gtrsim 5$ in the era of JWST. Using our fiducial simulation, we explore a range of spectral synthesis prescriptions and dust attenuation models, demonstrating that suitably chosen parameters can reproduce the observed UV luminosity functions (UVLFs) over $5 \leq z \leq 10$. In all cases, the inferred dust-to-metal ratio evolves with redshift, although its normalization at fixed redshift varies by a factor of $\sim 7$, depending on the adopted dust--metallicity scaling and attenuation curve. These model variations introduce substantial scatter in predictions for the $B$-band luminosity function, the H$\alpha$ luminosity function, the UV slope--UV magnitude relation, the stellar mass--Balmer ratio relation, and the relation between stellar and nebular colour excesses. Simultaneously reproducing these observables across multiple redshifts will therefore be essential for constraining dust models at high redshift with forthcoming observations. Observations of galaxies spanning a broad range of stellar masses with the Atacama Large Millimeter/submillimeter Array (ALMA) will provide particularly strong and independent constraints on dust properties. Our fiducial models underpredict the UV luminosity function at $z \geq 10$ relative to current observations, even when adopting a top-heavy IMF and neglecting dust attenuation. We find that galaxy properties are not fully converged at these redshifts in our simulation, indicating that higher-resolution simulations are required to robustly model galaxies at $z > 10$. We further emphasize that degeneracies between feedback prescriptions used in our simulation and dust properties must be carefully addressed when interpreting high-redshift observations and calibrating galaxy formation models.