H-I ABSORPTION AND OH-EMISSION IN IC 694/NGC-3690

The interaction system IC 694/NGC 3690 (Arp 299-Mrk 171) has been studied in H I absorption and OH emission with the VLA in the A-configuration. H I has been observed against all compact radio continuum sources within the extended radio structure. The OH megamaser emission is only seen against the strongest radio continuum source in the system located at the nucleus of IC 694. The H I velocity field in the system can be understood if velocity components of both galaxies are present at each of the absorption sites. H I gas from IC 694 is seen in absorption at the nucleus of NGC 3690 and vice versa. The H I absorption and OH emission at the nuclear source of IC 694 shows the presence of a large-scale rotating disk but also an absorption feature at the velocity of NGC 3690 and an expanding feature with a velocity offset of -160 km s-1. The H I data suggest that the systemic velocities of NGC 3690 and IC 694 are respectively 3050 and 3140 km s-1, slightly higher than the optical determinations. The molecular and infrared properties at the nucleus of IC 694 are most suitable for producing the right conditions for OH megamaser activity. The consistent modeling of the starbursts in Arp 299 suggests lifetimes of the starbursts in the different regions of a few times 107 yr, which is consistent with the understanding of OH megamasering.