The Compact Group of Galaxies HCG 31 in an Early Phase of Merging

We have obtained high spectral resolution (R = 45,900) Fabry-Perot velocity maps of the Hickson compact group HCG 31 in order to revisit the important problem of the merger nature of the central object A+C and to derive the internal kinematics of the candidate tidal dwarf galaxies in this group. Our main findings are as follows: (1) double kinematic components are present throughout the main body of A+C, which strongly suggests that this complex is an ongoing merger; (2) regions A2 and E, to the east and south of complex A+C, present rotation patterns with velocity amplitudes of ~25 km s-1, and they counterrotate with respect to A+C; and (3) region F, which was previously thought to be the best example of a tidal dwarf galaxy in HCG 31, presents no rotation and negligible internal velocity dispersion, as is also the case for region A1. HCG 31 presents an undergoing merger in its center (A+C), and it is likely that it has suffered additional perturbations due to interactions with the nearby galaxies B, G, and Q.