Structural and dynamical properties of Tidal dwarf galaxies in the tails and bridge of the Guitar galaxy Arp 105

Abstract

We present a multi-wavelength (far-ultraviolet to infrared) analysis of two tidal dwarf galaxy (TDG) candidates and a tidal bridge in the interacting system Arp 105 at $z=0.029$ in the Abell 1185 cluster. Far-ultraviolet observations obtained with the Ultraviolet Imaging Telescope onboard AstroSat reveal strong FUV emission from the tidal galaxies Arp~105N and Arp~105S, indicating recent star formation. In Arp~105N, strong nebular emission lines and large equivalent widths $EW(H\alpha )=77.6\pm 1.3$ $\stackrel{\circ }{\mathrm{A}}$ and $EW(H\beta )=15.8\pm 1.7$ $\stackrel{\circ }{\mathrm{A}}$ imply a dominant starburst age of $\sim$6 - 10~Myr under an instantaneous-burst assumption, while the FUV emission suggests star formation sustained over the past $\sim 100-200$~Myr. The relatively high metallicity, $\sim 2/3,Z_{\odot }$ (based on the strong-line method), is consistent with expectations for a tidal dwarf galaxy formed from material inherited from the host galaxy. Together, these results suggest that Arp~105N hosts a composite stellar population, consisting of older stars stripped from the host galaxy and younger stars formed in situ. Spectral energy distribution modeling yields stellar masses of $5.75\times 10^9$, $0.8\times 10^9$, and $6.8\times 10^9,{\mathrm{M}}_{\odot }$ for Arp~105N, Arp~105S, and the tidal bridge, respectively. Based on the dynamical mass estimate from VLA HI measurements for Arp~105N and based on CFHT H$\alpha$ kinematics for A105S, they have a dynamical-to-baryonic mass ratio of $\sim 1.95$ and $\sim 1.30$, respectively, indicating a deficiency of dark matter. Further observations, particularly integral field spectroscopy and high-resolution 21~cm observations, may provide better constraints into the kinematics and improve understanding of TDG formation.