the stellar warp is significantly smaller (by a factor of approximately two). They conclude that this comparison shows that the different components react differently to the forces responsible for the origin of the warp. The most important additional information that we provide here (not yet been discussed by other authors) is a multiwavelength study of galactic warps in one NIR and three optical filters.

Considerable effort has gone into establishing the physical origin and stability of warps. Numerous mechanisms have been proposed and explored, but they have thus far not provided a definitive and satisfactory physical explanation (see, e.g., the reviews by Binney 1992; Battaner et al. 1997; van der Kruit 2007). Kerr (1957), Hunter & Toomre (1969), Weinberg (1998), Weinberg & Blitz (2006), and others have suggested that warps can result from tidal interactions with a satellite or neighbouring galaxy. This hypothesis can explain warps neither in isolated galaxies (Sancisi 1976; Tubbs & Sanders 1979; Sparke 1984) nor in the Milky Way, if the latter was produced by an interaction with the Large Magellanic Cloud (see García-Ruiz et al. 2002a). Hunter & Toomre (1969) and Dekel & Shlosman (1983) proposed that the Galactic warp is a result of oscillations 