NGC 1808 is a peculiar southern spiral galaxy and rather nearby example of nuclear starburst activity ( $L_{\rm FIR} \approx 2 \times 10^{10}$ L$_{\odot}$); for a comprehensive overview see Koribalski (1993). Well known are the prominent dust filaments which emerge nearly perpendicular to its central disk (Véron-Cetty & Véron 1985; Laustsen, Madsen & West 1987), similar to those observed in M 82, indicating continuing disk-halo interactions. The nuclear region contains a number of bright `hot spots', which are mostly interpreted as very bright HII regions (Sérsic & Pastoriza 1965; Alloin & Kunth 1979; Koribalski & Dettmar 1993). In the actual nucleus, however, Véron-Cetty & Véron drew attention to the presence of a broad Seyfert-like component of H$\alpha$ with FWHM about 550 kms^-1. Radio observations at 6 cm reveal a number of very small (<1) compact sources in the central region, most likely to be supernovae and supernova remnants (Saikia et al. 1990).

VLA measurements of its nuclear region reveal that the broad ( $\Delta v \approx$ 360 kms^-1) HI absorption line seen at low angular resolution is a much narrower line which shifts its centre velocity over the face of the continuum (Koribalski, Dickey & Mebold 1993). This is interpreted as a torus of cold, dense gas with a rotation velocity of $\sim$250 kms^-1 and radius 500 pc. The gravitational mass required to explain this fast rotation is a few times 10⁹M$_{\odot}$. Figures 5 and 6 display the overall HI distribution and velocity field of the galaxy NGC 1808. The central `hole' is caused by HI absorption.

The radius and velocity of the nuclear ring are comparable to the distribution and kinematics of the optically visible `hot spots'. The possibility of a molecular gas ring has been considered by Dahlem et al. (1990) and is also indicated in new CO(2-1) data by Aalto et al. (1994).

A stellar bar (length $\sim$ 3 or 6 kpc), which was discovered in the H$\alpha$ line (Phillips 1993; Koribalski & Dettmar 1993), might be causing the gas to accumulate at the inner and outer Lindblad resonances. The inner Lindblad resonance as determined from the bar pattern speed coincides with the ring radius; the outer resonance lies just outside the pseudo-ring which is formed by the outer spiral arms.

Figure 5: HI distribution of the starburst galaxy NGC 1808.

Figure 6: HI mean velocity field of NGC 1808 (for a full description see Koribalski 1993). These data were taken with the BnC and AnB arrays of the VLA (5 h each).