2020MNRAS.496.2531P

We use dust masses (M_dust) derived from far-infrared data and molecular gas masses (M_mol) based on CO luminosity to calibrate proxies based on a combination of the galaxy Balmer decrement, disc inclination, and gas metallicity. We use such proxies to estimate M_dust and M_mol in the local SDSS sample of star-forming galaxies (SFGs). We study the distribution of M_dust and M_mol along and across the main sequence (MS) of SFGs. We find that M_dust and M_mol increase rapidly along the MS with increasing stellar mass (M_*), and more marginally across the MS with increasing SFR (or distance from the relation). The dependence on M_* is sub-linear for both M_dust and M_mol. Thus, the fraction of dust (f_dust) and molecular gas mass (f_mol) decreases monotonically towards large M_*. The star formation efficiency (SFE, inverse of the molecular gas depletion time) depends strongly on the distance from the MS and it is constant along the MS. As nearly all galaxies in the sample are central galaxies, we estimate the dependence of f_dust and f_gas on the host halo mass and find a tight anticorrelation. As the region where the MS is bending is numerically dominated by massive haloes, we conclude that the bending of the MS is due to a lower availability of molecular gas mass in massive haloes rather than a lower efficiency in forming stars.