peculiar galaxy

A peculiar galaxy is a galaxy that has some abnormality of shape, size, or content that sets it apart from the normal ellipticals, spirals, and irregulars in the Hubble classification of galaxies. Peculiar galaxies often result from galaxy interactions, or may shown some other distinctive feature such as jets emerging from the nucleus, unusual amounts of dust, or low surface brightness. They are denoted by the addition of "p" or "pec" to their main classification type. The Halton Arp's catalogue (1966) is devoted to peculiar galaxies.