The Chemical Evolution of Low Surface Brightness Galaxies

We have derived oxygen and nitrogen abundances of a sample of late-type, low surface brightness galaxies (LSBs) found in the Sloan Digital Sky Survey (SDSS). Furthermore, we have computed a large grid (5000 models) of chemical evolution models (CEMs) testing various time-scales for infall, baryon densities and several power-law initial mass functions (IMFs) as well. Because of the rather stable N/O-trends found both in CEMs (for a given IMF) and in observations, we find that the hypotheses that LSBs have stellar populations dominated by low-mass stars, i.e., very bottom-heavy IMFs (see Lee et al. 2004), can be ruled out. Such models predict much too high N/O-ratios and generally too low O/H-ratios. We also conclude that LSBs probably have the same ages as their high surface brightness counterparts, although the global rate of star formation must be considerably lower in these galaxies.