Resolved dust-gas-metallicity relations in nearby spiral galaxies

Abstract

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. We investigate dust-to-gas and dust-to-metal ratios (DGR and DMR) as functions of the gas-phase metallicity (Z) on spatial scales ranging from 0.6 to 2.3 kpc, in a sample of ten nearby spiral galaxies spanning more than an order of magnitude in stellar mass (9.7 łe łog(M_*/M_⊙) łeq 11.0), star formation rate (SFR, ∼0.3--3 , M_⊙ , ̊m -1 ), and metallicity ranging from 8.3 łesssim 12 + łog(̊m O/H) łesssim 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 (α_̊m CO). We homogeneously combined maps of dust, atomic gas, molecular gas, and metallicity. Motivated by the diversity in L_̊m CO(1-0)/SFR ratios and metallicity across our sample, we introduced a hybrid α_̊m CO prescription to distinguish between CO-bright and CO-dark regimes. The derived DGR--Z and DMR--Z relations were compared with other global and resolved observational results, and with the predictions of dust and chemical evolution models. Both DGR--Z and DMR--Z relations are dependent on the adopted α_̊m CO prescription, and no single α_̊m CO can reproduce the properties of the entire sample, motivating the use of a hybrid approach. The DGR increases with metallicity, spanning ∼1 dex across the sampled range, while the DMR remains approximately constant at łog( ) = -0.53 ± 0.13, implying that ∼30$%$ of metals are locked into dust grains. This flat behaviour indicates an evolved dust phase where efficient ISM grain growth drives a saturation regime balancing dust formation and destruction. DMR