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An optical Hα, CO, and H I survey of six low surface-brightness galaxies from the Schombert and Bothun catalog is presented. These galaxies are all late-type, low H I mass disk systems with unusually low-luminosity densities. Overall, the sample exhibits several paradoxical properties such as no detectable CO emission (a mean upper limit of MH₂__/MHI__<0. 10) despite normal H I surface density, very blue colors without evidence of strong star formation, weak H II regions lacking in massive stars and high M/L's. These properties suggest two possible star-formation histories for this class of objects centering on (1) inefficient star formation in a very metal-poor environment and (2) star formation which occurs preferentially outside of the giant molecular cloud environment with an IMF operating in suppressed high mass mode.
Schombert et al. (Thu,) studied this question.