The main results concerning the properties of H ii regions located within bars can be expressed as follows:
1) From standard diagnostic diagrams, the excitation of most H ii regions appears normal and similar to the one of disc regions. There are some exceptions for nuclear regions where an ionization mechanism other than photoionization seems to be present. However, there is marginal evidence that the ionization parameter in bar regions is lower than in disc regions, suggesting that the properties of the OB associations might be different in bar environments.
2) The electronic density distribution as derived from the[S ii]line ratio is similar to that observed for normal disc regions. The mean density is cm-3. Star formation regions in bars have the same "compactness" as disc regions.
3) The H/H extinction indicator reveals that, on average, bar regions have a visual extinction mag, 0.3 mag more than disc regions. This difference is mainly due to the fact that some regions are located near the bar dust lanes of the earlier types of galaxies in our sample.
4) The average H equivalent width for the bar regions is about 250 Å, half that of disc regions. While this could indicate an older population for bar H ii regions, the corresponding age difference is probably too small to be significant owing to the large uncertainties introduced by the galactic continuum correction.
5) The O/H abundance distribution of these H ii regions is remarkably homogeneous. This is the result of the gaseous radial flows in bars inducing mixing of the ISM, as seen on a larger scale in the discs of barred spirals.
© European Southern Observatory (ESO) 1999
Online publication: June 17, 1999