1508.06017
What drives the M*-SFR relation turning over at high masses? the role of bulges
Pan, et al
It is unclear whether bulge growth is responsible for the flattening of the SF MS at the high mass end. To investigate the role of bulges in shaping the MS, compare the NUV-r color between the central (r<R_50) and other regions for a sample of 6401 local SF galaxies. The NUV-r color is a good sSFR indicator. Find that at M*<1e10.2 Msun, the central NUV-r is on average only ~0.25 mag redder than the outer NUV-r. Above M*=1e10.2 Msun, the central NUV-r becomes systematically much redder than the outer NUV-r for more massive galaxies, indicating that the central bulge is more evolved at the massive end. When dividing the galaxies according to their Sersic index n, find that galaxies with n>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*. This suggests that star formation in bulges is more strongly dependent on n (or central mass density) that on B/T. Finally, find that the fraction of galaxies with n>2.0 rapidly increases with M* at M*>1e10.2 Msun, which is consistent with the turning over of the MS at the same transition mass. Conclude that the increasing fraction of low-sSFR dense bulges in M*>1e10.2 Msun galaxies, rather than increasing B/T, is responsible for the flattened slope of the M*-SFR relation at high masses.
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