Two-dimensional warm gas kinematics in interacting galaxy systems

Gas reservoirs, internal or acquired, play an important role in the secular evolution of interacting galaxies, since they are able to enhance/trigger star formation episodes and, probably, feed the activity of active galactic nuclei. Using Fabry-Perot observations, we have mapped, in the H line, the warm (T approximate to 10(4))gas distribution and the velocity fields of the galaxy members of five interacting, gas-rich galaxy systems. We investigated two M51-like systems (Arp 70 and Arp 74), two systems containing highly disrupted members (WBL 366 and RR 24) and a case of merging in progress (Arp 299, one of the nearest luminous infrared objects). We detected gas motions following the elongated arm/tail of Arp 70b, while in the fainter member of the pair of galaxies, Arp 70a, the gas distribution is off-centred with respect to the stellar isophotes, suggesting an external acquisition. Our kinematic data highlighted non-circular motions in the velocity field of one of the members of Arp 74 (Arp 74a). The two galaxies of the RR 24 system are connected by one tidal tail, through which the kinematically disturbed component RR 24b seems to supply warm gas to RR 24a. In spite of the nearly irregular gas distribution and perturbed morphology, WBL 366a (the star-forming galaxy VV-523) and WBL 366b have nearly regular velocity fields. The velocity field in the Arp 299 system is irregular, and gas flow between the two nuclei is detected. The present observations, discussed in the light of model predictions and complementary observations from the literature, suggest that all these systems are still probably in an early phase of the encounter. However, the ionized gas distribution and kinematics are strongly influenced by tidal forces. In particular, cross-fuelling mechanisms between galaxies are in action. In Arp 299 the warm and cold gaseous components show similar kinematic properties, although the cold gas seems to maintain a still better organized motion with respect to the warm gas.