NGC 6040

NGC 6040 is a spiral galaxy located about 550 million light-years away in the constellation Hercules. NGC 6040 was discovered by astronomer Édouard Stephan on June 27, 1870. NGC 6040 is interacting with the lenticular galaxy PGC 56942. As a result of this interaction, NGC 6040's southern spiral arm has been warped in the direction toward PGC 56942. NGC 6040 and PGC 56942 are both members of the Hercules Cluster.
NGC 6040 was classified in the 1966 Atlas of [Peculiar Galaxies] by Halton Arp, who listed it as Arp 122. However, Mr. Arp mistakenly identified NGC 6040 as NGC 6039, which is not part of any Arp object.

Neutral hydrogen depletion

NGC 6040 and PGC 56942 are both depleted of their neutral hydrogen content. This depletion may have been caused as both galaxies fell into the Hercules Cluster and interacted with the surrounding intracluster medium. This interaction would have caused ram-pressure stripping and in effect removed the gas in the two galaxies.