THE DISTRIBUTION AND NATURE OF STAR-FORMATION REGIONS IN NGC-1792

A strong asymmetry with respect to the major axis has been found in the spatial distribution of H II regions in NGC 1792 detected on our H alpha image. In the radio continuum, this asymmetry is even stronger than in H alpha, indicating that supernova activity set in earlier in the northeastern half of the disk than southwest of the nucleus. This suggests that we are viewing spatially propagating star formation (SF) in the disk, which set in about 10(7) yr ago. The most luminous H II regions are distinctly different from the rest of the star-forming regions in NGC 1792, showing up as a peak in the H alpha luminosity near L(H alpha) similar or equal to 3 x 10(39) ergs s(-1) Around these giant H II regions large amounts of diffuse ionized gas are found, suggesting that this gas is heated by UV radiation escaping these regions. Attributing the radiation coming from the luminous H II regions to a temporarily increased level of SF activity, we estimate that on the order of 1200 OB stars were formed in each of them, with integrated Lyman-continuum luminosities in the range of 6 x 10(51) s(-1). Although increased significantly near the galactic turnover of rotation, the global SF rate in NGC 1792 is only marginally affected (similar to 20%) by this phenomenon. The most plausible explanation of these results and those obtained for NGC 1808, the interaction partner of NGC 1792, is that the currently on-going SF was triggered by an interaction some 10(8) yr ago.