1995A&A...295..605B

The results of a long observation in the 21 cm neutral hydrogen line of the highly warped gaslayer of the edge-on galaxy NGC 4013 are presented. The previous, shorter observations, allowed data with a resolution of 30"x30", full width at half maximum. Presently, with a much higher resolution of 13"x19"(FWHM), individual channel maps, total HI map and integrated position-velocity diagram are presented. In general a confirmation is given of the earlier conclusions. At first, the warp is highly symmetric and extends to large heights above the plane of the galaxy. Secondly, the warp onset appears right at the position where the photometry indicates the edge of the stellar disk. And, thirdly, the rotational velocity drops by approximately 25km/s just at this optical edge. This has to imply that at that position not only the light, but also the disk mass density has to approach zero. The additional resolution of the new observations allows the determination not only of the exact orientation of the warp, but also of the gas density and warp angle as a function of radius. Furthermore, the considerably improved position-velocity diagram makes it possible to construct a detailed rotation curve. These analyses are only possible using a proper modelling procedure. This procedure, the results and conclusions are described in a forthcoming paper.