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

Abstract

We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate(SFR)-stellarmass(M*)relation, called the main sequence(MS)of star-forming galaxies , for star-forming and all galaxies outto~z5. We measure the MS using mean stacks of 3 GHz radio-continuum images to derive average SFRs for∼200,000 mass-selected galaxies at z>0.3 in the COSMOSfield. We describe the MS relation by adopting anew model that incorporates a linear relation at low stellar mass(log(M*/Me)<10)and aflattening at high stellarmass that becomes more prominent at low redshift(z < 1.5).Wefind that the SFR density peaks at 1.5<z<2,and at each epoch there is a characteristic stellar mass(M*=1-4 x 1010Me)that contributes the most to theoverall SFR density. This characteristic mass increases with redshift, at least toz ∼ 2.5. Wefind no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy numberdensity at 0.3<z<3, nor for galaxies in X-ray groups atz ∼ 0.75. We confirm that massive bulge-dominatedgalaxies have lower SFRs than disk-dominated galaxies at afixed stellar mass atz < 1.2. As a consequence, theincrease in bulge-dominated galaxies in the local star-forming population leads to aflattening of the MS at highstellar masses. This indicates that "mass quenching" is linked with changes in the morphological composition ofgalaxies at afixed stellar mass. Show more