The dispersion of the star-formation main sequence ( SFMS ) reflects the diversity of star formation histories and variation in star formation rates ( SFRs ) in star-forming galaxies ( SFGs ) with similar stellar masses ( M ^ { \ast } ) .
We examine the dispersion of local SFMS using a complete sample of Sloan Digital Sky Survey galaxies at 0.01 < z < 0.03 with \log ( M ^ { \ast } / M _ { \odot } ) > 8.8 .
The SFRs are estimated from H \alpha in combination with 22 \mu m observation from WISE .
We measure the dispersion of specific SFR ( SSFR ) as a function of M ^ { * } .
We confirm that the dispersion increases with M ^ { * } from 0.37 \pm 0.01 dex at \log ( M ^ { \ast } / M _ { \odot } ) < 9.6 to 0.51 \pm 0.02 dex at \log ( M ^ { \ast } / M _ { \odot } ) > 10.2 .
Despite star formation is mostly associated with disks , the dispersion of disk SSFR still increases with M ^ { * } .
We conclude that the presence of bulges/bars is likely responsible for the large dispersion of SSFR in massive SFGs while low-mass SFGs are mostly disk-dominated and thus with small dispersion .
Our results suggest that star formation on galactic scales is dramatically affected by central dense structures through both enhancing and/or quenching processes ; while lower-mass SFGs tend to have less bursty star formation histories .
However , the dispersion of SSFR becomes significantly smaller and remains constant when only disk-dominated SFGs are counted .
This finding implies that the impact of stochastic stellar feedback on star formation is likely to follow the same pattern in all disk galaxies , showing no correlation with halo potential .