The Atlas of Peculiar Galaxies is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The primary goal of the catalog was to present photographs of examples of the different kinds of peculiar structures found among galaxies.
Background[]
Arp at the time, realized that the reason why galaxies formed into spiral or elliptical shapes was not well understood. He perceived peculiar galaxies as small "experiments" that astronomers could use to understand the physical processes that distort spiral or elliptical galaxies. With this atlas, astronomers had a sample of peculiar galaxies that they could study in more detail. The atlas does not present a complete overview of every peculiar galaxy in the sky but instead provides examples of the different phenomena as observed in nearby galaxies.
In more recent times, the peculiarities seen in the Arp atlas are thought to be well understood.
List of Arp galaxies[]
| Image | Designation | Common name | Type | Constellation |
|---|---|---|---|---|
 |
Arp 1 | NGC 2857 | Spiral galaxy | Ursa Major |
 |
Arp 2 | UGC 10310 | Dwarf spiral galaxy | Hercules |
  |
Arp 3 | PGC 69293 | Dwarf spiral galaxy | Aquarius |
  |
Arp 10 | UGC 1775 | Ring Galaxy | Cetus |
  |
Arp 78 | NGC 772 | Unbarred spiral galaxy | Aries |
  |
Arp 85 | Whirlpool Galaxy | Grand design spiral galaxy | Canes Venatici |
  |
Arp 148 | Mayall's Object | Ring Galaxy | Ursa Major |
  |
Arp 273 | Rose Galaxies | Spiral Galaxy, Barred Spiral Galaxy | Andromeda |
  |
Arp 319 | Stephan's Quintet | Galaxy Cluster | Pegasus |
A list of Arp galaxies is currently a work in progress.