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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≈</mml:mo> <mml:mn>6</mml:mn> <mml:mo>-</mml:mo> <mml:mn>11</mml:mn> </mml:math> . 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>&lt;</mml:mo> <mml:mn>7</mml:mn> </mml:math> , 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>&gt;</mml:mo> <mml:mn>9</mml:mn> </mml:math> the MS is already well in place at z = 5–7, for galaxies with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≈</mml:mo> <mml:mn>7</mml:mn> <mml:mo>-</mml:mo> <mml:mn>8</mml:mn> </mml:math> it only becomes significant at z &lt; 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.