Extented ionized gas emission and kinematics of the compact group galaxies in HCG 16: Signatures of mergers

Abstract

We report on kinematic observations of Ha emission line from four late-type galaxies of Hickson Compact Group 16 (H16a,b,c and d) obtained with a scanning Fabry-Perot interferometer and samplings of 16 km/s and 1". The velocity fields show kinematic peculiarities for three of the four galaxies: H16b, c and d. Misalignments between the kinematic and photometric axes of gas and stellar components (H16b,c,d), double gas systems (H16c) and severe warping of the kinematic major axis (H16b and c) were some of the peculiarities detected. We conclude that major merger events have taken place in at least two of the galaxies group. H16c and d, based on their significant kinematic peculiarities, their double nuclei and high infrared luminosities. Their Ha gas content is strongly spatially concentred - H16d contains a peculiar bar-like structure confined to the inner $\sim$ 1 h^-1 kpc region. These observations are in agreement with predictions of simulations, namely that the gas flows towards the galaxy nucleus during mergers, forms bars and fuel the central activity. Galaxy H16b, and Sb galaxy, also presents some of the kinematic evidences for past accretion events. Its gas content, however, is very spare, limiting our ability to find other kinematic merging indicators, if they are present. We find that isolated mergers, i.e., they show an anormorphous morphology and no signs of tidal tails. Tidal arms and tails formed during the mergers may have been stripped by the group potential (Barnes & Hernquist 1992) ar alternatively they may have never been formed. Our observations suggest that HCG 16 may be a young compact group in formation throught the merging of close-by objects in a dense environment.