What drives the M*-SFR relation turning over at high masses? The role of bulges

Abstract

It is unclear whether bulge growth is responsible for the flattening of the star formation main sequence (MS) at the high mass end. To investigate the role of bulges in shaping the MS, we compare the NUV$-r$ color between the central ($r 2.0 tend to be redder in the central NUV$-r$ color than those with $n$<2.0, even at fixed B/T and $M_{\ast}$. This suggests that star formation in bulges is more strongly dependent on $n$ (or central mass density) than on B/T. Finally, we find that the fraction of galaxies with $n$>2.0 rapidly increases with $M_{\ast}$ at $M_{\ast}>10^{10.2}M_{\sun}$, which is consistent with the turning over of the MS at the same transition mass. We conclude that the increasing fraction of low-sSFR dense bulges in $M_{\ast}>10^{10.2}M_{\sun}$ galaxies, rather than increasing B/T, is responsible for the flattened slope of the $M_{\ast}$$-$SFR relation at high masses.