Arp 332 – A Chain of Galaxies in Eridanus
Arp 332 is a grouping of galaxies located in the constellation of Eridanus, included by Halton Arp in his Atlas of Peculiar Galaxies. Unlike compact galaxy groups, Arp 332 stands out because of the elongated arrangement of its members, forming what appears to be a genuine chain of galaxies.
Its main members are NGC 1228, NGC 1229, NGC 1230, and IC 1892, although different catalogues and studies may include other faint objects located in the same field. Arp’s catalogue classifies Arp 332 among the so-called chains of galaxies.
The scene is particularly interesting because several of the galaxies display peculiar morphologies or signs of disturbance. However, we should not assume that all the objects appearing close together in the sky necessarily form a single physically bound system: identifying the members and determining possible interactions depends on their distances and radial velocities.
🌌 A Chain of Galaxies
Arp 332 lies in a region of the sky belonging to Eridanus, one of the largest constellations in the night sky.
The four main galaxies are distributed over several arcminutes, forming a visually elongated structure. NGC 1228, NGC 1229, NGC 1230, and IC 1892 are listed together under the designation Arp 332 in different astronomical catalogues.
Halton Arp studied this type of configuration because some peculiar galaxies could provide information about the interactions and dynamical processes that modify galactic structures.
In a later study of peculiar galaxy systems, Arp described Arp 332 as a relatively loose chain of five or six galaxies, also pointing out the presence of possible interacting pairs within the chain.
Arp 332 is therefore interesting not only because of its visual appearance, but also because it represents one of the systems included in Arp’s catalogue for the study of peculiar galaxy groupings and morphologies.
📸 Images from LilTecan
Arp 332 is a particularly interesting target for deep-sky astrophotography.
The main galaxies are relatively faint and lie close together in the same field. In a short exposure, only the brightest galaxies may be visible, while a deep integration can reveal the fainter components surrounding the chain.
From LilTecan, beneath the exceptional skies of La Palma, a long integration allows us to explore this region of Eridanus and reveal the structure of the chain in greater depth.
A combination of LRGB filters is particularly well suited to representing the different galaxies while preserving the contrast between their central regions and their outer structures.
🌟 Structure and Main Characteristics
Arp 332 is primarily formed by a chain of galaxies in which the following objects stand out:
- NGC 1228, one of the brightest galaxies in the group.
- NGC 1229, classified as a peculiar spiral galaxy.
- NGC 1230, a smaller and fainter galaxy located within the chain.
- IC 1892, a peculiar spiral galaxy located toward one end of the system.
The Arp catalogue and later sources also identify other faint objects in this region, including MCG-04-08-029. The exact list of members can vary depending on the catalogue used and the criteria applied to define the grouping.
One of the striking features of Arp 332 is precisely the morphological diversity of its galaxies. Some display spiral structures, while others have peculiar or difficult-to-classify shapes.
🔭 A Window into Galactic Interactions
Galaxies do not necessarily evolve in isolation. When several galaxies approach one another, gravity can modify their structures, produce distortions, and redistribute gas and stars.
Arp 332 is particularly interesting in this context because Halton Arp himself pointed out the presence of possible galaxy pairs within the chain. In his 1973 study, he described the system as a relatively loose chain and mentioned two pairs that could be interacting.
Nevertheless, apparent proximity in an astronomical image alone does not prove that two galaxies are interacting. Establishing a physical relationship requires considering, among other factors, their redshifts and distances.
This caution is especially important for Arp 332, where different sources may include different numbers of galaxies as members of the system.
🌌 Arp 332 from La Palma
Observing Arp 332 is like looking at a small region of the Universe where several galaxies appear aligned, creating an extraordinarily striking structure.
Each of these tiny points and patches of light represents a galaxy located at enormous distances from the Milky Way. Some clearly reveal their spiral structures, while others appear as small diffuse patches because of their lower apparent brightness.
From LilTecan, a deep integration allows us to go far beyond what a direct visual observation can reveal and bring out the fainter galaxies accompanying the main members of the chain.
Arp 332 is, ultimately, an excellent example of how Halton Arp’s Atlas of Peculiar Galaxies brings together systems whose appearance is particularly interesting for studying the diversity and possible interactions of galaxies.