| Abstract: Galaxy–galaxy interaction and merger remnants provide an ideal laboratory for studying the formation
of tidal debris and tidal dwarf galaxies (TDGs). Since TDGs form from baryonic material stripped from
interacting parent galaxies, they are expected to contain little or no dark matter, although observational
constraints remain limited. We present a multi-wavelength (far-ultraviolet to infrared) analysis of two tidal
dwarf galaxy 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 aboard AstroSat reveal
strong FUV emission from the tidal features Arp 105N and Arp 105S, indicating recent star formation.
In Arp 105N, strong nebular emission lines and large equivalent widths (𝐸𝑊 (𝐻𝛼) = 77.6 ± 1.3 ˚A and
𝐸𝑊 (𝐻 𝛽) = 15.8 ± 1.7 ˚A) imply a dominant starburst age of ∼6-10 Myr under an instantaneous-burst
assumption, while the FUV emission suggests star formation sustained over the past several tens of Myr. In
addition to this young stellar component, Arp 105N shows evidence for an older stellar population through
the detection of Na D2 𝜆5890 ˚A stellar absorption, indicating a composite stellar population inherited
from the parent galaxy and formed in situ. Spectral energy distribution modeling yields stellar masses
of 5.7 × 109, 0.8 × 109, and 3.4 × 109, M⊙ for Arp 105N, Arp 105S, and the tidal bridge, respectively.
Using the virial theorem and a stellar velocity dispersion corrected for instrumental broadening, 𝜎true,LOS =
(67.0 ± 1.7), km s−1, we estimate a dynamical mass of 𝑀dyn,105N (4𝑅e) = (1.8 ± 0.1) × 1010 𝑀⊙ . The
resulting dynamical-to-baryonic mass ratio of ∼1.5, together with the relatively high metallicity (∼ 2/3, 𝑍⊙ ),
is consistent with expectations for a tidal dwarf galaxy with little or no dark matter. |
