A panchromatic spatially resolved analysis of nearby galaxies - II. The main sequence - gas relation at sub-kpc scale in grand-design spirals

Abstract

In this work, we analyse the connection between gas availability and the position of a region with respect to the spatially resolved main-sequence (MS) relation. Following the procedure presented in Enia et al. (2020), for a sample of five face-on, grand design spiral galaxies located on the MS we obtain estimates of stellar mass and star formation rate surface densities (Σ<SUB>⋆</SUB> and Σ<SUB>SFR</SUB>) within cells of 500 pc size. Thanks to H I 21cm and <SUP>12</SUP>CO(2-1) maps of comparable resolution, within the same cells we estimate the surface densities of the atomic (Σ<SUB>H I</SUB>) and molecular ( $\Sigma _{\rm {H_2}}$ ) gas and explore the correlations among all these quantities. Σ<SUB>⋆</SUB>, Σ<SUB>SFR</SUB>, and $\Sigma _{\rm {H_2}}$ define a 3D relation whose projections are the spatially resolved MS, the Kennicutt-Schmidt law and the molecular gas MS. We find that $\Sigma _{\rm {H_2}}$ steadily increases along the MS relation and is almost constant perpendicular to it. Σ<SUB>H I</SUB> is nearly constant along the MS and increases in its upper envelope. As a result, Σ<SUB>SFR</SUB> can be expressed as a function of Σ<SUB>⋆</SUB> and Σ<SUB>H I</SUB>, following the relation log Σ<SUB>SFR</SUB> = 0.97log Σ<SUB>⋆</SUB> + 1.99log Σ<SUB>H I</SUB> - 11.11. We show that the total gas fraction significantly increases towards the starburst regions, accompanied by a weak increase in star formation efficiency. Finally, we find that H<SUB>2</SUB>/H I varies strongly with the distance from the MS, dropping dramatically in regions of intense star formation, where the UV radiation from newly formed stars dissociates the H<SUB>2</SUB> molecule, illustrating the self-regulating nature of the star formation process.