2019MNRAS.485L..93R

We report Giant Metrewave Radio Telescope H I 21 cm imaging of CGCG 137-068, the host galaxy of the fast-evolving luminous transient (FELT) AT2018cow. This is the first study of the gas properties of a FELT host galaxy. We obtain a total H I mass of (6.6 ± 0.9) x 10⁸ M_☉ for the host galaxy, which implies an atomic gas depletion time of 3 Gyr and a gas-to-stellar mass ratio of 0.47, consistent with values in normal star-forming dwarf galaxies. At spatial resolutions of >=6 kpc, the H I of CGCG 137-068 appears to be distributed in a disc, in mostly regular rotation. However, at spatial resolutions of 2 kpc, the highest column density H I is found to lie in an asymmetric ring around the central regions, with H I column densities >=10²¹ cm^–2; AT2018cow lies within this high column density ring. This H I ring could be suggestive of an interaction between CGCG 137-068 and a companion galaxy. Such a ring is ideal for the formation of compact regions of star formation hosting massive stars, favouring massive star progenitor models for AT2018cow. We measure a 1.4 GHz flux density of 1.13 ± 0.13 mJy for AT2018cow on 2018 August 27.