HI Spatial Distribution in the Galaxy NGC 3783

We have mapped the emission from atomic hydrogen at λ=21 cm from the galaxy NGC 3783 with the Australia Telescope Compact Array. Our main results are: a) the HI morphology is irregular and perturbed, gathered in three blobs apparently unrelated to the optical morphology ; b) the observed HI velocity distribution indicates a normal disk in differential rotation with a constant velocity out to a radius of 160 ′′ (30 kpc), c) the inclination of the disk is about 25 • with the kinematic major axis at a position angle slightly different from that of the stellar bar, d) the HI mass inside a radius of 18 ′′ is only 2.1 × 10 7 M ⊙ , the total HI mass within 180 ′′ is 1.1 × 10 9 M ⊙ and the dynamical mass is 2 × 10 11 M ⊙. The bulk of the gas in NGC 3783 is outside the diameter of the stellar bar; e) Numerical simulations of the gas flow in the barred potential derived from the red image indicate that the pattern speed is Ω p = 38 km/s/kpc: the ring of Hα emitting regions encircling the bar would then correspond to UHR, and the Hα accumulation in the center to a nuclear ring. Various possibilities are discussed to account for the active nucleus fuelling.