The Emergence of the Star Formation Main Sequence with Redshift Unfolded by JWST

Abstract We investigate the correlation between stellar mass ( M ⋆ ) and star formation rate (SFR) across the stellar mass range log 10 ( M ⋆ / M ⊙ ) ≈ 6 - 11 . We consider almost 50,000 star-forming galaxies at z ≈ 3–7, leveraging data from COSMOS/SMUVS, JADES/GOODS-S, and MIDIS/XDF. This is the first study spanning such a wide M ⋆ range without relying on gravitational lensing effects. We locate our galaxies on the SFR– M ⋆ plane to assess how the location of galaxies in the star formation main sequence (MS) and starburst (SB) region evolves with M ⋆ and redshift. We find that the two star-forming modes tend to converge at log 10 ( M ⋆ / M ⊙ ) 7 , with all galaxies found in the SB mode. However, deeper observations will be instrumental for reaching lower SFRs and M ⋆ to further validate this scenario. By dissecting our galaxy sample in M ⋆ and redshift, we show that the emergence of the star formation MS is M ⋆ dependent: while in galaxies with log 10 ( M ⋆ / M ⊙ ) > 9 the MS is already well in place at z = 5–7, for galaxies with log 10 ( M ⋆ / M ⊙ ) ≈ 7 - 8 it only becomes significant at z < 4. Overall, our results are in line with previous findings that the SB mode dominates among low stellar-mass galaxies. The earlier emergence of the MS for massive galaxies is consistent with galaxy downsizing.