shown in Fig. \[morfo\], where the hatched area shows all galaxies and the cross-hatched area covers warped galaxies. The warp frequency does not seem to depend significantly on galaxy morphology, except for S0 and very-late-type galaxies, which both yield lower frequencies.

A noticeable result from Sánchez-Saavedra et al. (2003) was that S0 galaxies are generally not warped. This places strong constraints on any hypothesis proposed to explain warps. Among our sample galaxies, ESO311-G12 has a small warp in both the optical and the NIR, but both of the other S0 sample galaxies, ESO358-G26 and ESO358-G29, do not exhibit any detectable warps. Although our sample only contains three S0 galaxies, so that we cannot draw any statistical conclusions on that basis, our results are not in contradiction to previously published results.

Since we have data in both optical and NIR bands, we can compare both, enabling us to either detect or reject colour dependences in the warps. This comparison is difficult, however, because of inherent uncertainties and because the differences as a function of wavelength are not very large. Five of our galaxies (ESO235-G53, ESO288-G25, ESO311-G12, ESO416-G25, and ESO555-G36) show similar warp curves in all four observed bands, one galaxy (ESO531-G22) 