The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence (SFR-M-*) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 +/- 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around M-* approximate to 10(10) M-circle dot and can also be seen in the gas mass-stellar mass plane. The global Kennicutt-Schmidt law (SFR-M-g) has a slope of 1.47 +/- 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only similar to 3% of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with M-* < 10(10) M-circle dot), while massive spirals (with M-* > 10(10) M-circle dot) are weary giants that constitute more of a turn-off population.