Abundance gradients in low surface brightness spirals: clues on the
  origin of common gradients in galactic discs
  We acquired spectra of 141 HII regions in ten late-type low surface
brightness galaxies (LSBGs). The analysis of the chemical abundances obtained
from the nebular emission lines shows that metallicity gradients are a common
feature of LSBGs, contrary to previous claims concerning the absence of such
gradients in this class of galaxies. The average slope, when expressed in units
of the isophotal radius, is found to be significantly shallower in comparison
to galaxies of high surface brightness. This result can be attributed to the
reduced surface brightness range measured across their discs, when combined
with a universal surface mass density-metallicity relation. With a similar
argument we explain the common abundance gradient observed in high surface
brightness galaxy (HSBG) discs and its approximate dispersion. This conclusion
is reinforced by our result that LSBGs share the same common abundance gradient
with HSBGs, when the slope is expressed in terms of the exponential disc scale
length.
