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

Abstract

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, NGC 4656UV. Using Fabry–Perot and GMOS multislit 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 |$\beta = -0.027\, \pm \,$|0.029 dex kpc−1, 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 |$6.8^{1.8}_{-0.6}\times 10^{9}$| M|$\odot$| 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 (Vmax/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.