Metal-THINGS: Gas metallicity gradients in nearby galaxies

¹ Departamento de Física de la Tierra y Astrofísica, Fac. de C.C. Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
² Instituto de Física de Partículas y del Cosmos, IPARCOS, Fac. C.C. Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
³ Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Luis E. Erro No. 1, Sta. Ma. Tonantzintla, Puebla, C.P. 72840 Mexico
⁴ Consejo Nacional de Humanidades, Ciencias y Tecnologías, Av. Insurgentes Sur 1582, 03940 Ciudad de México, Mexico
⁵ Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 Munich, Germany
⁶ Main Astronomical Observatory, National Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St, 03680 Kiev, Ukraine
⁷ Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio av. 3, 10257 Vilnius, Lithuania
⁸ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁹ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
¹⁰ INAF – Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy
¹¹ Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales y Ciclo Básico Común, Buenos Aires, Argentina
¹² CONICET-Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina
¹³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁴ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán, 58089 Mexico
¹⁵ Dipartimento di Fisica e Astronomia, Alma Mater Studiorum Università di Bologna, via Piero Gobetti 93/2, I-40129 Bologna, Italy
¹⁶ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan 1, 44001 Teruel, Spain

^⋆ Corresponding author.

Received: 20 January 2025
Accepted: 11 July 2025

Abstract

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.