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

Z.-X. Fu, C. Sengupta, Ramya Sethuram, Bikram Pradhan, M. Singh, K. Misra, T. C. Scott, Y. -Z. Ma

We present results from our Giant Metrewave Radio Telescope (GMRT) Hi, Himalayan Chandra Telescope (HCT) Hα, 1 m Sampurnanand Telescope (ST) and 1.3 m Devasthal Fast Optical Telescope (DFOT) deep optical observations of the 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 H I map shows no H I detection associated with KUG 2359+311, nor any H I tail or bridge-like structure connecting KUG 2359+311 to the NGC 7805/6 system. Our HCT Hα image, on the other hand, displays strong detections in KUG 2359+311, with net SFR ~ 0.035 ± 0.009 M yr−1. The Hα data constrain the redshift of KUG 2359+311 to 0.00 ≤ z ≤ 0.043, compared to the redshift of NGC 7806 of ~ 0.015. TDGs detected to date have all been H i rich, and displayed H i, ionised gas and stellar tidal debris trails (bridges or tails) linking them to their parent systems. However, neither our H i data nor our optical imaging, while three magnitudes deeper than SDSS, reveals a tidal trail connecting KUG 2359+311 to NGC 7805/6. Lack of H i, presence of an old stellar population, ongoing star formation and 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.

galaxies: dwarf; galaxies: interactions; galaxies: spiral; galaxies: star formation; galaxies: peculiar; radio lines: galaxies; Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics

Reports on progress in physics
Volume 21, Number 2, Page 8
2021 March

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia