Resolved Dust-Gas-Metallicity relations in nearby spiral galaxies

Abstract

Context: Understanding the interstellar medium (ISM) requires high-resolution, multi-component mapping to capture its complex physical structure. Nearby spiral galaxies, with their abundant and diverse ISM, provide an ideal laboratory for such a comprehensive analysis at sub-galactic scales. Aims: We investigate dust-to-gas (DGR) and dust-to-metal (DMR) ratios as a functions of gas-phase metallicity (Z), on spatial scales ranging from 0.6 to 2.3 kpc, in a sample of 10 nearby spiral galaxies, spanning more than an order of magnitude in stellar mass (9.7 \le \log(M_*/M_\odot) \leq 11.0), star formation rate (SFR, \sim 0.3--3 \, M_\odot \, \rm yr^{-1}) and metallicity ranging from 8.3 \lesssim 12 + \log( O/H) \lesssim 8.8. We explore how the DGR-Z and DMR-Z relations are shaped by the assumptions behind the CO-to-H_2 conversion factor (\alpha_{CO}). Methods: We homogeneously combine maps of dust, atomic gas, molecular gas, and metallicity. Motivated by the diversity in L_{CO(1-0)}/SFR ratios and metallicity across our sample, we introduce a hybrid \alpha_{CO} prescription to distinguish between CO-bright and CO-dark regimes. The derived DGR-Z and DMR-Z relations are compared with other global and resolved observational results, and with the predictions of dust and chemical evolution models. Results: Both DGR-Z and DMR-Z relations are dependent on the adopted \alpha_{CO} prescription, and no single \alpha_{CO} can reproduce the properties of the entire sample, motivating the use of a hybrid approach. The DGR increases with metallicity, spanning \sim 1 dex across the sampled range; while the DMR remains approximately constant at \log(\mathrm{DMR}) = -0.53 \pm 0.13, implying that \sim 30 \% of metals are locked into dust grains. This flat behavior indicates an evolved dust phase where efficient ISM grain growth drives a saturation regime balancing dust formation and destruction.