Metal-THINGS: Gas metallicity gradients in nearby galaxies

Aims. This paper explores and analyses the gas metallicity gradients in a sample of 25 nearby galaxies using new integral field spectroscopy observations from the Metal-THINGS survey, for a total of 102 individual pointings. We derive and analyse the resolved diffuse ionised gas content, Baldwin, Phillips, & Terlevich diagrams, and gas metallicities for our entire sample, at spatial resolutions of 40–300 pc. Gas metallicity gradients are studied as a function of the galaxy’s stellar mass, H I gas fraction, and diffuse ionised gas content, and using different parametric length scales for normalisation. Methods. The metallicity gradients are analysed using Bayesian statistics based on data from the Metal-THINGS survey. Bayesian MCMC models are developed to explore how metallicity gradients vary with a galaxy’s mass and how they correlate with properties such as the stellar mass or the atomic gas fraction. Additionally, we compare and contrast our results with those from other works that use the same metallicity calibration. Results. For our sample, we find that the metallicity typically decreases with galactic radius, consistent with inside-out galaxy growth. We find a trend dependent on the stellar mass, with a break at log( M star / M ⊙ )≃9.5, and another between the metallicity gradients and the atomic gas fraction ( f g, H I ) of a galaxy at f g, H I ≃ 0.75, indicating shallower gradients for lower gas fractions. These results are consistent with previous studies on galaxies with comparable stellar mass regimes and morphologies. We find that normalisation using NUV-band effective radii is preferable for galaxies with a higher atomic gas content and lower stellar masses, while r-band radii are better suited for those with lower atomic gas fractions and more massive ones. Conclusions. Our results highlight a strong connection between gas content, stellar mass, and metallicity gradients. The breaks at log( M ⋆ / M ⊙ )≃9.5 and f g, H I ≃ 0.75 mark shifts in chemical enrichment behaviour, with low-mass galaxies showing greater sensitivity to gas processes. Overall, this points to gas accretion and removal as key drivers of chemical evolution in low-mass systems.