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H I, star formation and tidal dwarf candidate in the Arp 305 system

C. Sengupta, T. C. Scott, S. Paudel, K. S. Dwarakanath, D. J. Saikia, B. W. Sohn

Abstract

We present results from our Giant Metrewave Radio Telescope (GMRT) H I observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT H I mapping, compared to previous observations, allowed detailed study of smaller scale features. Our H I analysis supports the conclusion in Hancock et al. that the most recent encounter between the pair occurred ∼4×108 yr ago. The GMRT observations also show H I features near NGC 4017 that may be remnants of an earlier encounter between the two galaxies. The H I properties of the bridge TDG candidate include MHi∼6.6×108 M and VHi=3500±7 km s−1, which are in good agreement with the velocities of the parent galaxies. Additionally, the TDG's H I linewidth of 30 km s−1 and modest velocity gradient together with its star formation rate of 0.2 M yr−1 add to the evidence favouring the bridge candidate being a genuine TDG. The bridge TDG's Spitzer 3.6 and 4.5 μm counterparts with a [3.6]−[4.5] colour ∼ −0.2 mag suggests that stellar debris may have seeded its formation. Future spectroscopic observations could confirm this formation scenario and provide the metallicity, which is a key criterion for the validation of TDG candidates.

Keywords
galaxies: dwarf; galaxies: individual: Arp 305; galaxies: interactions; galaxies: spiral; galaxies: star formation

Monthly Notices of the Royal Astronomical Society
Volume 469, Issue 3, Page 12
2017 August

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