Program: GN-2011A-Q-30

The initial mass function (IMF) of star-forming galaxies with very low rates of star formation and low surface brightness (LSB) appears to be depleted of massive stars, compared to systems with higher rates of star formation. This result has been recently obtained by independent studies working on different samples of star-forming galaxies, and, if confirmed, will have deep repercussions on our understanding of galaxy evolution. A decrease in the number of massive stars relative to the number of intermediate-mass stars in LSB galaxies would leave a measurable trace in the chemical abundance ratios of the ionized interstellar medium. In particular, the N/O ratio would be enhanced. We propose to measure for the first time reliable N/O ratios for a number of HII regions in a sample of LSB galaxies, in order to test the variability of the upper IMF in these systems.