Prototypical Ultraluminous Galaxy Arp 220
Prototypical ultraluminous galaxy Arp 220 mapped in 21cm HI emission
at the VLA in contours superposed over a deep R-band CCD image. Two
gas rich disk galaxies have merged, and the HI traces the gaseous
outer disk thrown out in tidal tails. See
J. Hibbard's WEB page
for more pretty images of such train wrecks.