Abundances of H II Regions in Early-Type Spiral Galaxies
M.S. Oey and R.C. Kennicutt
We present an abundance study of H II regions in 15 Sa to Sb galaxies. We
find that the metal abundances of these H II regions are systematically
higher than those in Sc and later type galaxies, although this effect is
not a function of Hubble type only. The distribution of
reddening values is similar to late-type spirals, indicating that
the dust levels associated with our sample of H II regions
are not unusually high. This implies that the systematic changes in
H II region luminosity along the Hubble sequence are due to intrinsic
differences in the properties of the gas and ionizing OB associations,
rather than to differences in extinction. Our data also suggest
that the abundance gradients in early-type galaxies may
generally be flatter than in Sc galaxies. The
metallicities within our sample exhibit no correlation with galaxy
mass, suggesting that mass is not the only factor driving the observed
gas-phase abundances among luminous M_B < -20 spiral galaxies. We
have also computed photoionization models of metal-rich (0.5 - 3 Z_sol) H II
regions, in order to evaluate the reliability of the Pagel & Edmunds
R23 empirical abundance parameter in this abundance range. The
results indicate that R23 provides a valuable means of ranking
relative abundances in this regime, but systematic variations in other
parameters, most notably nebular density and stellar effective
temperature, introduce significant uncertainties into the abundance scales.
1993 ApJ 411, 137
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