The distribution of neutral hydrogen and the velocity field of the galaxy NGC 3109.

Summary. The irregular-type galaxy NGC 3109 has been observed in the 21 cm hydrogen line with the Nancay radio telescope. The H I content is found to be 2.2 x 1O M0, or 20 % of the total mass of 1.1 x 1010 M0 The H I has a flat-topped distribution, being reasonably well represented by a gaussian function. It has a greater extent to the south-west than in other directions. There is a low-density component of H I in the outer regions. Parameters of the H I distribution and the rotation curve are deduced by a model-fitting procedure. There are significant departures from circular motion outside a distance of 20' arc. A value of 10 km/s for the velocity dispersion was found all over the galaxy. Key words: H I - galaxies - kinematics