HI 21cm mapping of the host galaxy of AT2018cow: a fast-evolving luminous transient within a ring of high column density gas

Abstract

We report Giant Metrewave Radio Telescope (GMRT) HI 21cm 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 HI mass of $(6.6\pm 0.9)\times 10^8$ M${}_{\odot }$ 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 $\ge 6$ kpc, the HI of CGCG 137-068 appears to be distributed in a disk, in mostly regular rotation. However, at spatial resolutions of $2$ kpc, the highest column density HI is found to lie in an asymmetric ring around the central regions, with HI column densities $\ge 10^{21}$ cm${}^{-2}$; AT2018cow lies within this high column density ring. This HI 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 which are likely progenitors of FELTs. We measure a 1.4 GHz flux density of $1.13\pm 0.13$ mJy for AT2018cow on 2018 August 27.

Accepted for publication in MNRAS Letters. For the definitive version visit https://academic.oup.com/mnras. 5 pages, 3 figures, 1 table

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