A giant intergalactic H I bubble near Arpl43

We present observations of the nearby ring galaxy Arpl43 (NGC2445/4) and describe the discovery of a giant H I shell 20 kpc across, lying 100 kpc from Arpl43. The shell, which shows evidence for line splitting near its centre, lies in a long H I filament pointing towards the Arpl43 system. We suggest that the shell is an expanding bubble of H I, and is direct evidence for a powerful galactic-scale explosion 10⁸ years ago which we associate with a strong burst of star formation. We believe that both the ring galaxy and the giant bubble have their origin in the passage of a gas-rich companion through the inner disk of NGC2445, and its subsequent disruption.