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

## TL;DR

This study uses GMRT HI 21cm imaging to analyze the gas properties of the host galaxy of the transient AT2018cow, revealing a high-density gas ring potentially linked to star formation and the transient's progenitor.

## Contribution

First HI 21cm imaging study of a FELT host galaxy, identifying a high-density gas ring possibly related to transient progenitors.

## Key findings

- Host galaxy has a total HI mass of (6.6 ± 0.9) × 10^8 M⊙.
- HI distribution shows a ring with high column density around the galaxy center.
- AT2018cow is located within a high-density HI ring.

## 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 $\geq 6$ 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 $\geq 10^{21}$ 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.