Exploring the interplay of dust and gas phases in DustPedia star-forming galaxies

Molecular gas is the key ingredient in the star formation cycle, and tracing its dependencies on other galaxy properties is essential for understanding galaxy evolution. In this work, we explore the relation between the different phases of the interstellar medium (ISM), namely molecular gas, atomic gas, and dust, and galaxy properties using a sample of nearby late-type galaxies. To this end, we collected CO maps that cover at least 70% of the optical extent for 121 galaxies from the DustPedia project, which ensured an accurate determination of MH2, the global molecular gas mass. We investigated which scaling relations provide the best description of MH2, based on the strength of the correlation and its intrinsic dispersion. We found that the commonly used correlations between MH2 and star formation rate (SFR) and stellar mass (M⋆), respectively, are affected by large scatter, which accounts for galaxies that are experiencing quenching of their star formation activity. This issue can be partially mitigated by considering a “fundamental plane” of star formation, fitting together MH2, M⋆, and SFR. We confirm previous results from the DustPedia collaboration that the total gas mass has the tightest connection with the dust mass, and that the molecular component also establishes a good correlation with dust once map-based MH2 estimates are used. Although dust grains are necessary for the formation of hydrogen molecules, the strength of gravitational potential driven by the stellar component plays a key role in driving density enhancements and the atomic-to-molecular phase transition. By investigating the correlations between the various components of the ISM and monochromatic luminosities at different wavelengths, we propose mid- and far-IR luminosities as reliable proxies of $ \mathrm {L^{\prime}_{CO(1-0)}} $ for those sources that lack dedicated millimeter observations. Luminosities in mid-IR photometric bands collecting PAH emission can be used to trace molecular gas and dust masses.