Interacting system NGC 7805/6 (Arp 112) and its tidal dwarf galaxy candidate

Abstract: We present results from our Giant Metrewave Radio Telescope (GMRT) HI, Himalayan Chandra Telescope (HCT) Halpha, 1m Sampurnanand Telescope (ST) and 1.3m Devasthal Fast Optical Telescope (DFOT) deep optical observations of NGC 7805/6 (Arp 112) system to test KUG 2359+311's tidal dwarf galaxy (TDG) candidacy and explore the properties of the interacting system. Our GMRT HI map shows no HI detection associated with KUG 2359+311, nor any HI tail or bridge-like structure connecting KUG 2359+311 to the NGC 7805/6 system. Our HCT Halpha image on the other hand, shows strong detections in KUG 2359+311, with net SFR ~ 0.035$\pm 0.009 {\rm M}_{\odot}\,{\rm yr}^{-1}$. The Halpha data constrains the redshift of KUG 2359+311 to $0.00 \le z \le 0.043$, compared to the redshift of NGC 7806 of ~ 0.015. TDGs detected to date have all been HI rich, and displayed HI, ionised gas and stellar tidal debris trails (bridges or tails) linking them to their parent systems. But neither our HI data nor our optical images, while three magnitudes deeper than SDSS, reveal tidal trail connecting KUG 2359+311 to NGC 7805/6. Lack of HI , presence of an old stellar population, ongoing star formation, reasonably high SFR compared to normal dwarf galaxies suggest that KUG 2359+311 may not be an Arp 112 TDG. It is most likely a case of a regular gas-rich dwarf galaxy undergoing a morphological transformation after having lost its entire gas content to an interaction with the Arp 112 system. Redshift and metallicity from future spectroscopic observations of KUG 2359+311 would help clarify the nature of this enigmatic structure.