We have derived oxygen and nitrogen abundances of a sample of late-type, low surface brightness (LSB) galaxies 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 LSB galaxies 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 LSB galaxies 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.
تحميل البحث