Extended ionized gas emission and kinematics of the compact group galaxiesin Hickson Compact Group 16: Signatures of mergers

We report on kinematic observations of Ha emission from four late-type gala xies of Hickson Compact Group 16 (H16a, b, c, d) obtained with a scanning F abry-Perot interferometer and samplings of 16 km s(-1) and 1 ". The velocit y fields show kinematic peculiarities for three of the four galaxies: H16b, H16c, and H16d. Misalignments between the kinematic and photometric axes o f gas and stellar components (H16b-H16d), double gas systems (H16c) and sev ere warping of the kinematic major axis (H16b and H16c) were some of the pe culiarities detected. We conclude that major merger events have taken place in at least two of th e galaxies of the group, H16c and H16d, based on their significant kinemati c peculiarities, their double nuclei, and their high infrared luminosities. Their H alpha gas content is strongly spatially concentrated; H16d contain s a peculiar barlike structure confined to the inner similar to 1 h(-1) kpc region. These observations are in agreement with predictions of simulation s, namely, that the gas hows toward the galaxy nucleus during mergers, form s bars, and fuels the central activity. Galaxy H16b, an Sb galaxy, also pre sents some of the kinematic evidence for past accretion events. Its gas con tent, however, is very sparse, limiting our ability to find other kinematic merging indicators, if they are present. We find that the merger remnants in the compact group HCG 16 have significantly smoother optical profiles th an isolated mergers, i.e., they show an amorphous morphology and no signs o f tidal tails. Tidal arms and tails formed during the mergers may have been stripped by the group potential, or, alternatively, they may have never be en formed. The velocity field of the galaxy H16a shows grand-design isovelocity lines with no signs of disturbances inside a radius of similar to R-25. This resu lt is contrary to expectations given that the galaxy has a high infrared lu minosity, central activity, tidal tails at large radii, and is embedded in a common group envelope observed in H I and X-rays. The normality of the ve locity field suggests that this galaxy may be a fairly recent acquisition o f the compact group. Our observations suggest that HCG 16 may be a young compact group in format ion through the merging of close-by objects in a dense environment.