Jan 15 2020
Blue contours correspond to the neutral hygrogen ring, overlaid on an optical color composite image obtained at CFHT in g-, r- and i-band.
Bait et al. report the discovery using the Giant Metrewave Radio Telescope of an extremely large (diameter approximately 115 kpc) neutral hydrogen (HI) ring, off-centred from a massive quenched galaxy, AGC 203001. The ring does not have a bright extended optical counterpart unlike several other known ring galaxies. Bait et al. present deep g-, r-, and i-band optical imaging of the HI ring, using the MegaCam instrument on the Canada-France-Hawaii Telescope, which shows several regions with faint optical emission at a surface brightness level of approximately 28 mag. per square arcsec. Such extended HI structures are rare, with only one other case known so far — the Leo ring. Conventionally, off-centred rings have been explained by a collision with an “intruder” galaxy, leading to expanding density waves of gas and stars in the form of a ring. However, in such a scenario the impact also leads to large amounts of star formation in the ring which is not observed in the ring presented in this paper. Alternatively, such a ring could also form due to tidal interactions with a neighbouring galaxy or even major mergers. The exact physical mechanism for the formation of such rings is still under debate.
Article : Discovery of a large Hi ring around the quiescent galaxy AGC 203001, O. Bait, S. Kurapati, P.-A. Duc et al., MNRAS, 492, 1, 1 (Février 2020)
Contact: Pierre-Alain Duc, pierre-alain.duc@astro.unistra.fr
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