The VLA-COSMOS 3 GHz Large Project: Evolution of Specific Star Formation Rates out to z ∼ 5

<jats:title>Abstract</jats:title> <jats:p>We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate (SFR)–stellar mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>) relation, called the main sequence (MS) of star-forming galaxies , for star-forming and all galaxies out to <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaba044ieqn1.gif" xlink:type="simple"/> </jats:inline-formula>. We measure the MS using mean stacks of 3 GHz radio-continuum images to derive average SFRs for ∼ 200,000 mass-selected galaxies at <jats:italic>z</jats:italic> > 0.3 in the COSMOS field. We describe the MS relation by adopting a new model that incorporates a linear relation at low stellar mass (log(<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) < 10) and a flattening at high stellar mass that becomes more prominent at low redshift (<jats:italic>z</jats:italic> < 1.5). We find that the SFR density peaks at 1.5 < <jats:italic>z</jats:italic> < 2, and at each epoch there is a characteristic stellar mass (<jats:italic>M</jats:italic> <jats:sub>*</jats:sub> = 1–4 × 10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) that contributes the most to the overall SFR density. This characteristic mass increases with redshift, at least to <jats:italic>z</jats:italic> ∼ 2.5. We find no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy number density at 0.3 < <jats:italic>z</jats:italic> < 3, nor for galaxies in X-ray groups at <jats:italic>z</jats:italic> ∼ 0.75. We confirm that massive bulge-dominated galaxies have lower SFRs than disk-dominated galaxies at a fixed stellar mass at <jats:italic>z</jats:italic> < 1.2. As a consequence, the increase in bulge-dominated galaxies in the local star-forming population leads to a flattening of the MS at high stellar masses. This indicates that “mass quenching” is linked with changes in the morphological composition of galaxies at a fixed stellar mass.</jats:p>