6 Discussion

We have determined the central velocity dispersion in 42 spiral galaxies. For 32 of them, we have presented profiles of the projected rotation velocity and velocity dispersion, along the major axis. The compilation of Prugniel & Simien (1996) indicates that $\sigma_0$ has been so far published for 16 of these objects, and extended kinematical profiles for only nine objects.

Together with those of Paper I, our results gather $\sigma_0$ determinations for 75 galaxies, and kinematical profiles for 64 of them; they significantly increase the limited amount already available in the literature: for all nearby spirals obeying the same selection criteria as ours, for instance, $\sigma_0$ values are so far available for less than 200 objects, and a stellar rotation curve for a few tens of them.

The accuracy of our reductions is statistically similar to that of SP; we recall that, for early-type galaxies, their kinematical measurements have contributed to the thorough study of several aspects of the Fundamental Plane (Prugniel & Simien 1994, 1996, 1997). For the present sample, direct comparison to measurements from other sources is not straightforward. Although we are able to calculate spatial resolution effects for most of our galaxies, very few other sources allow to do the same, and comparison of raw measurements is not always relevant. Let us, however, mention that for 26 galaxies in common with other works, the mean value of the raw $\Delta \sigma_0$ residuals (ours - theirs) is $-10 \, {\rm km \, s}^{-1}$, with a rms scatter of 22 km s^-1, and with no visible trend as a function of $\sigma_0$. Although marginally indicative, these small values enhance the confidence in the lack of significant systematic errors on our measurements.

For the objects observed under very poor seeing conditions, the main effect should obviously be on $\sigma_0$, but factor $f_{\rm bulge}$ provides a partial correction, and its values stay in the range (0.92-1.02), not much wider than for the whole sample.

Our results can be used for applications involving several structural and kinematical aspects. In a forthcoming paper, we will study the mass-to-light ratios of the bulge and disk components of spirals for which surface photometry is also available.

Acknowledgements

We are indebted to the telescope operators at the Observatoire de Haute-Provence for their help in collecting the data. We thank the referee, C. Moellenhof, for his report. We have made use of the Lyon-Meudon Extragalactic Database operated by the LEDA team.