Exploring the intrinsic scatter of the star-forming galaxy main sequence at redshift 0.5 to 3.0

Previous studies have shown that the normalization and scatter of the galaxy ‘main sequence’ (MS), the relation between star formation rate (SFR) and stellar mass (M_∗), evolves over cosmic time. However, such studies often rely on photometric redshifts and/or only rest-frame UV to near-IR data, which may underestimate the SFR and M_∗ uncertainties. We use MAGPHYS + photo-z to fit the UV to radio spectral energy distributions of 12 380 galaxies in the COSMOS field at 0.5 < z < 3.0, and self-consistently include photometric redshift uncertainties on the derived SFR and M_∗. We quantify the effect on the observed MS scatter from (1) photometric redshift uncertainties (which are minor) and (2) fitting only rest-frame ultraviolet to near-infrared observations (which are severe). At fixed redshift and M_∗, we find that the intrinsic MS scatter for our sample of galaxies is 1.4 to 2.6 times larger than the measurement uncertainty. The average intrinsic MS scatter has decreased by 0.1 dex from z = 0.5 to ∼2.0. At low z, the trend between the intrinsic MS scatter and M_∗ follows a functional form similar to an inverse stellar mass-halo mass relation (SMHM; M_∗/M_halo versus M_∗), with a minimum in intrinsic MS scatter at log (M_∗/M_☉) ∼ 10.25 and larger scatter at both lower and higher M_∗, while this distribution becomes flatter for high z. The SMHM is thought to be a consequence of feedback effects and this similarity may suggest a link between galaxy feedback and the intrinsic MS scatter. These results favour a slight evolution in the intrinsic MS scatter with both redshift and mass.