We describe a sub-galactic main sequence ( SGMS ) relating star formation rate surface density ( \Sigma _ { \textrm { SFR } } ) and stellar mass density ( \Sigma _ { \star } ) for distinct regions within star forming galaxies , including their nuclei .
We use a sample of 246 nearby star-forming galaxies from the “ Star Formation Reference Survey ” and demonstrate that the SGMS holds down to \sim 1 kpc scales with a slope of \alpha = 0.91 and a dispersion of 0.31 dex , similar to the well-known main sequence ( MS ) measured for globally integrated star formation rates ( SFRs ) and stellar masses .
The SGMS slope depends on galaxy morphology , with late-type galaxies ( Sc–Irr ) having \alpha = 0.97 and early-type spirals ( Sa–Sbc ) having \alpha = 0.81 .
The SGMS constructed from sub-regions of individual galaxies has on average the same characteristics as the composite SGMS from all galaxies .
The SGMS for galaxy nuclei shows a dispersion similar to that seen for other sub-regions .
Sampling a limited range of SFR–M _ { \star } space may produce either sub-linearity or super-linearity of the SGMS slope .
For nearly all galaxies , both SFR and stellar mass peak in the nucleus , indicating that circumnuclear clusters are among the most actively star-forming regions in the galaxy and the most massive .
The nuclear SFR also correlates with total galaxy mass , forming a distinct sequence from the standard MS of star-formation .
The nuclear main sequence will be useful for studying bulge growth and for characterizing feedback processes connecting AGN and star formation .