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Discovery of a large HI ring around the quiescent galaxy AGC 203001

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

This news has been featured in Discover magazine, Eurekalert, phys.org, theprint.in, Hindustan Times, Indian Express, Sakal Times, International Business Times, Business Insider, Deccan Herald, First Post.

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