Kinematics and physical properties of the nearby galaxy NGC 4656 and its TDG candidate

Interacting galaxies provide us with an excellent laboratory for studying a number of physical phenomena associated with these processes. In this paper, we present a spectroscopic and kinematic analysis of the interacting galaxy NGC 4656 and its companion tidal dwarf galaxy (TDG) candidate, NGC4656UV. Using Fabry-Perot andGMOSmultislit data, we investigated the possible origin of NGC 4656UV. We found that NGC 4656UV has a low metallicity (12 + log(O/H)~8.2) and it follows the mass-metallicity relation for normal dwarf galaxies. For NGC 4656, we estimated a flat oxygen abundance gradient of β = -0.027±0.029 dex kpc, which suggests the presence of gas flows induced by gravitational interactions. By analysing radial velocity profiles and by fitting a kinematic model of the observed velocity field, we confirm the literature result that NGC 4656 consists of one single body instead of two objects. We estimated a dynamical mass of 6.8 × 10M and R of 12.1 kpc from the kinematic model of NGC 4656. Although the observed velocity field is dominated by rotation at large scales (V/σ ≳2.8), important non-rotational motions are present at small scales. Based on these new results, and on previously published information, we propose that NGC 4656 and 4656UV are a pair of interacting galaxies. NGC 4656UV is a companion of NGC 4656 and it does not have a tidal origin. The interaction between the two could have triggered the star formation in NGC 4656UV and increased the star formation in the north-east side of NGC 4656.