GHASP: an Hα kinematic survey of spiral and irregular galaxies - III. 15 new velocity fields and study of 46 rotation curves
We present Fabry-Pérot observations obtained in the frame of the GHASP survey (Gassendi Hα survey of SPirals). We have derived the Hα maps, the velocity fields and the rotation curves for a set of 15 galaxies. The data presented in this paper are combined with the data published in our two previous papers in order to make a preliminary analysis of the rotation curves obtained for 46 galaxies. We check the consistency of our data with the Tully-Fisher relationship and conclude that our Hα rotation curves reach the maximum velocity in most of the cases, even with solid-body rotating galaxies. We find that our rotation curves, on average, almost reach the isophotal radius R25. We confirm the trend, already mentioned by Rubin, Waterman & Kenney and Márquez et al., that the maximum extension of the Hα rotation curves increases with the type of the spiral galaxy, up to t~ 7-8 and we find that it decreases for magellanic and irregular galaxies. We also confirm the trend seen by Márquez et al. that later types tend to have lower values of the internal slope of the rotation curve, in agreement with Rubin et al.