We constrain the slope of the star formation rate ( \log \Psi ) to stellar mass ( \log \mathrm { M _ { \star } } ) relation down to \log ( \mathrm { M _ { \star } / M _ { \odot } } ) = 8.4 ( \log ( \mathrm { M _ { \star } / M _ { \odot } } ) = 9.2 ) at z = 0.5 ( z = 2.5 ) with a mass-complete sample of 39,106 star-forming galaxies selected from the 3D-HST photometric catalogs , using deep photometry in the CANDELS fields .
For the first time , we find that the slope is dependent on stellar mass , such that it is steeper at low masses ( \log \mathrm { \Psi } \propto \log \mathrm { M _ { \star } } ) than at high masses ( \log \mathrm { \Psi } \propto ( 0.3 - 0.6 ) \log \mathrm { M _ { \star } } ) .
These steeper low mass slopes are found for three different star formation indicators : the combination of the ultraviolet ( UV ) and infrared ( IR ) , calibrated from a stacking analysis of Spitzer/MIPS 24 \mu m imaging ; \beta -corrected UV SFRs ; and H \alpha SFRs .
The normalization of the sequence evolves differently in distinct mass regimes as well : for galaxies less massive than \log ( \mathrm { M _ { \star } / M _ { \odot } } ) < 10 the specific SFR ( \Psi / \mathrm { M _ { \star } } ) is observed to be roughly self-similar with \Psi / \mathrm { M _ { \star } } \propto ( 1 + z ) ^ { 1.9 } , whereas more massive galaxies show a stronger evolution with \Psi / \mathrm { M _ { \star } } \propto ( 1 + z ) ^ { 2.2 - 3.5 } for \log ( \mathrm { M _ { \star } / M _ { \odot } } ) = 10.2 - 11.2 .
The fact that we find a steep slope of the star formation sequence for the lower mass galaxies will help reconcile theoretical galaxy formation models with the observations .