4.2. Spatial Abundance Profiles
The spatial distribution of abundances in galaxies depends coarsely on the Hubble type. Spectroscopic study of H II regions in unbarred or weakly barred spiral galaxies typically reveals a strong radial gradient in metallicity (Figure 8), as determined from O/H (Zaritsky, Kennicutt, & Huchra (1994; ZKH); Vila-Costas & Edmunds 1992; VCE). The derived O/H can drop by a factor of ten to thirty or fifty from the nucleus of a galaxy to the outer disk as demonstrated in galaxies with well-sampled data. In those spirals with spectroscopy of more than ten H II regions covering the full radial extent of the disk, there is little evidence that O/H gradients deviate from exponential profiles. Irregular galaxies, by contrast, show little spatial variation in abundances, to high levels of precision (Kobulnicky & Skillman 1996), indicating a well-mixed ISM. The data for strongly barred spiral galaxies shows evidence that their O/H gradients are more shallow than in unbarred spirals. I will discuss these galaxies in more detailed in a later section.
A quick glance at data on O/H in galaxies (e.g. Figure 8 of ZKH) does not immediately reveal any trends of metallicity among galaxies of different types. However, detailed examination of this data shows that there are significant correlations between abundances and abundance gradients in spirals and irregulars with galaxy structural properties. Here I shall review some of these correlations and some implications. Note also that for the most part this discussion applies only to high surface brightness "normal" spirals.