2017MNRAS.472..166G

Low Surface Brightness Galaxies (LSBs), inspite of being gas rich, have low star formation rates and are therefore low surface brightness in nature. We calculate Q_RW, the 2-component disc stability parameter as proposed by Romeo & Wiegert, as a function of galactocentric radius R for a sample of five LSBs, for which mass models, as obtained from HI 21cm radio-synthesis observations and R-band photometry, were available in the literature. We find that the median value of Q_ RW_^ min^, the minimum of Q_RW over R, lies between 2.6 and 3.1 for our sample LSBs, which is higher than the median value of 1.8 ± 0.3 for Q_ RW_^ min^ for a sample of high surface brightness galaxies (HSBs) as obtained in earlier studies. This clearly shows that LSBs have more stable discs than HSBs, which could explain their low star formation rates and, possibly, their low surface brightness nature. Interestingly, the calculated values of Q_RW decrease only slightly (median Q_ RW_^ min^ ∼ 2.3-3) if the discs were taken to respond to the gravitational potential of the dark matter halo only, but reduce by ∼ a factor of 2-3 (median Q_ RW_^ min^ ∼ 0.7-1.5) if they respond to their self-gravity alone. This implies that the dark matter halo is crucial in regulating disc stability in LSBs, which may have important implications for models of galaxy formation and evolution.