Atlas of Peculiar Galaxies
Encyclopedia
The Atlas of Peculiar Galaxies is a catalog
Astronomical catalog
An astronomical catalog or catalogue is a list or tabulation of astronomical objects, typically grouped together because they share a common type, morphology, origin, means of detection, or method of discovery...

 of peculiar galaxies produced by Halton Arp
Halton Arp
Halton Christian Arp is an American astronomer. He is known for his 1966 Atlas of Peculiar Galaxies, which catalogues many examples of interacting and merging galaxies...

. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...

.

The primary goal of the catalog was to present photographs of examples of the different kinds of peculiar structures found among nearby galaxies. Arp realized that the reason why galaxies formed into spiral
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 or elliptical
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...

 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.

Because little was known at the time of publication about the physical processes that caused the different shapes, the galaxies in the atlas are sorted based on their appearance. Objects 1-101 are individual peculiar spiral galaxies or spiral galaxies that apparently have small companions. Objects 102-145 are elliptical and elliptical-like galaxies. Individual or groups of galaxies with neither elliptical nor spiral shapes are listed as objects 146-268. Objects 269-327 are double galaxies. Finally, objects that simply do not fit into any of the above categories are listed as objects 332-338. Most objects are best known by their other designations, but a few galaxies are best known by their Arp numbers (such as Arp 220
Arp 220
Arp 220 is the result of a collision between two galaxies which are now in the process of merging. Located 250 million light-years away in the constellation Serpens, it is the 220th object in Halton Arp's Atlas of Peculiar Galaxies.-Features:...

).

Today, the physical processes that lead to the peculiarities seen in the Arp atlas are now well understood. A large number of the objects are interacting galaxies, including M51 (Arp 85), Arp 220
Arp 220
Arp 220 is the result of a collision between two galaxies which are now in the process of merging. Located 250 million light-years away in the constellation Serpens, it is the 220th object in Halton Arp's Atlas of Peculiar Galaxies.-Features:...

, and the Antennae Galaxies (NGC 4038/NGC 4039, or Arp 244)
Antennae Galaxies
The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a phase of starburst. They were discovered by William Herschel in 1785...

. A few of the galaxies are simply dwarf galaxies that do not have enough mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 to produce enough gravity to allow the galaxies to form any cohesive structure. NGC 1569 (Arp 210)
NGC 1569
NGC 1569 is a dwarf irregular galaxy in Camelopardalis. While this faint galaxy is not a popular amateur astronomy target, it is well studied by professional astronomers, who are interested in the history of star formation within the galaxy. The galaxy is relatively nearby. Consequently, the...

 is an example of one of the dwarf galaxies in the atlas. A few other galaxies are radio galaxies. These objects contain active galactic nuclei that produce powerful jets of gas called radio jets. The atlas includes the nearby radio galaxies M87 (Arp 152)
Messier 87
Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...

 and Centaurus A (Arp 153)
Centaurus A
Centaurus A is a prominent galaxy in the constellation of Centaurus. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance...

.

Notable Arp galaxies

Arp Number Name Magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

Notes
26 Pinwheel Galaxy
Pinwheel Galaxy
The Pinwheel Galaxy is a face-on spiral galaxy distanced 21 million light-years away in the constellation Ursa Major, first discovered by Pierre Méchain on March 27, 1781, and communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final...

 (M101)
+7.5 spiral galaxy
37 Messier 77
Messier 77
Messier 77 is a barred spiral galaxy about 47 million light-years away in the constellation Cetus. Messier 77 is an active galaxy with an Active Galactic Nucleus , which is obscured from view by astronomical dust at visible wavelengths...

+8.9 radio galaxy
41 NGC 1232 +9.8 spiral galaxy
76 Messier 90
Messier 90
Messier 90 is a spiral galaxy about 60 million light-years away in the constellation Virgo. It was discovered by Charles Messier in 1781.- Membership of the Virgo Cluster :...

+9.5 spiral galaxy
77 NGC 1097
NGC 1097
NGC 1097 is a barred spiral galaxy about 45 million light-years away in the constellation Fornax. As of 2006, three supernovae have been observed in NGC 1097....

+9.5 galaxy interacting with its satellite
85 Whirlpool Galaxy
Whirlpool Galaxy
The Whirlpool Galaxy is an interacting grand-design spiral galaxy that is estimated to be 23 ± 4 million light-years from the Milky Way Galaxy. in the constellation Canes Venatici...

 (M51)
+8.4 galaxy interacting with its satellite
116 Messier 60
Messier 60
Messier 60 is an elliptical galaxy approximately 55 million light-years away in the constellation Virgo.-History:...

+8.8 colliding galaxies
152 Virgo A (M87) +8.6 elliptical galaxy
153 Centaurus A
Centaurus A
Centaurus A is a prominent galaxy in the constellation of Centaurus. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance...

 (NGC 5128)
+6.6 radio galaxy in a collision?
188 Tadpole Galaxy
Tadpole Galaxy
The Tadpole Galaxy is a disrupted barred spiral galaxy located 400 million light years from Earth toward the northern constellation Draco. Its most dramatic features are a trail of stars about 280 thousand light-years long and massive, bright blue star clusters.It is hypothesized that a more...

+14.4 galaxy finishing merging
242 Mice Galaxies
Mice Galaxies
NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years away, they are presently in the process of colliding and merging...

+14.7 colliding galaxies
244 Antennae Galaxies
Antennae Galaxies
The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a phase of starburst. They were discovered by William Herschel in 1785...

+10.3 colliding galaxies
317 Messier 65
Messier 65
Messier 65 is an intermediate spiral galaxy about 35 million light-years away in the constellation Leo. It was discovered by Charles Messier in 1780. M65, M66, and NGC 3628 comprise the famous Leo Triplet, a small group of galaxies.-Discovery:M65 was discovered by Charles Messier and included in...

+9.2 spiral galaxy
319 NGC 7320
NGC 7320
NGC 7320 is a spiral galaxy in the Stephan's Quintet. However, it is not an actual member of the galaxy group, but a much closer line-of-sight galaxy at a distance of about 40 million light years. Other galaxies of Stephan's Quintet are some 300 million ly distant....

+15 galaxy in colliding group
337 Cigar Galaxy (M82) +8.6 starburst galaxy


Low surface brightness galaxies

These are mostly dwarf galaxies or poorly-defined spiral galaxies (with the designation Sm) that have low surface brightnesses (i.e. they emit little light per unit area). Low surface brightness galaxies are actually quite common. The exception is NGC 2857 (Arp 1), which is an Sc spiral galaxy (which means that it has a definite structure with loosely-wound spiral arms and a faint but well-defined nucleus).
Arp Number Common Name Notes
1 NGC 2857 Sc spiral galaxy
2 UGC 10310
3 Arp 3
4 Arp 4
5 NGC 3664
6 NGC 2537
NGC 2537
NGC 2537 is a blue compact dwarf galaxy in the constellation Lynx. This is also known as Bear's Paw Galaxy, Arp 6, and Mrk 86. It belongs to the iE class of Blue Compact Dwarf classification, which is described as galactic spectra with an underlying smooth elliptical Low Surface Brightness...



Galaxies with split arms

This category contains spiral galaxies with arms that split into two separate parts.
Arp Number Common Name Notes
7 Arp 7
8 NGC 497
9 NGC 2523
10 UGC 1775 Contains an off-center nucleus
11 UGC 717
12 NGC 2608
NGC 2608
NGC 2608 is a barred spiral galaxy located 93 million light-years away in the constellation Cancer . It is 62,000 light-years across; about 60% of the width of the Milky Way...



Galaxies with detached segments

This category contains spiral galaxies with arms that appear to be segmented. Some spiral arm segments may appear detached because dust lanes in the spiral arms obscure the arms' starlight. Other spiral arms may appear segmented because of the presence of bright star clusters (or discontinuous chains of bright star clusters) in the spiral arms.
Arp Number Common Name Notes
13 NGC 7448
14 NGC 7314
NGC 7314
NGC 7314 is a spiral galaxy located in the constellation Piscis Austrinus. It is a Seyfert galaxy.Walter Scott Houston describes its appearance in small telescopes:...

15 NGC 7393
16 M66
Messier 66
Messier 66 is an intermediate spiral galaxy about 36 million light-years away in the constellation Leo. It was discovered by Charles Messier in 1780...

17 UGC 3972
18 NGC 4088
NGC 4088
NGC 4088 is an intermediate spiral galaxy in the constellation Ursa Major. The galaxy forms a physical pair with NGC 4085, which is located 11′ away.-Disk Structure:...



Three-armed spiral galaxies

Usually, most spiral galaxies contain two clearly defined spiral arms, or they contain only fuzzy filamentary spiral structures. Galaxies with three well-defined spiral arms are rare.
Arp Number Common Name Notes
19 NGC 145
NGC 145
NGC 145, also known as Arp 19, is an irregular galaxy in Cetus most well noted for its three spiral arms....

20 UGC 3014
21 Arp 21


One-armed spiral galaxies

One-armed spiral galaxies are also rare. In this case, the single spiral arm may actually be formed by a gravitational interaction with another galaxy.
Arp Number Common Name Notes
22 NGC 4027
NGC 4027
NGC 4027 is a barred spiral galaxy approximately 83 million light-years away in the constellation Corvus. It is also a peculiar galaxy because one of its spiral arms goes out more than the other...

23 NGC 4618
NGC 4618
NGC 4618 is a distorted dwarf galaxy in the constellation Canes Venatici. The galaxy is formally classified as a Sm galaxy, which means that its structure vaguely resembles the structure of spiral galaxies...

Interacting with NGC 4625
NGC 4625
NGC 4625 is a distorted dwarf galaxy in the constellation Canes Venatici. The galaxy is formally classified as a Sm galaxy, which means that its structure vaguely resembles the structure of spiral galaxies...

24 NGC 3445


Spiral galaxies with one heavy arm

The spiral arms in these galaxies have an asymmetric appearance. One spiral arm may appear to be considerably brighter than the other. In the photographic plates produced by Arp, the bright arm would look dark or "heavy". While most of these galaxies (such as M101
M101
M101 or M-101 may refer to:* Myasishchev M-101T Gzhel, an aircraft produced in Russia* Messier 101, or the Pinwheel Galaxy, a spiral galaxy in the constellation Ursa Major* M101 howitzer, a 105 mm light howitzer...

 and NGC 6946
NGC 6946
NGC 6946, , is an intermediate spiral galaxy about 22 million light-years away, on the border between the constellations Cepheus and Cygnus. It was discovered by William Herschel on September 9, 1798...

) are simply asymmetric spiral galaxies, NGC 6365 is an interacting pair of galaxies where one of the two galaxies is viewed edge-on and just happens to lie where the spiral arm for the other face-on galaxy would be visible.
Arp Number Common Name Notes
25 NGC 2276
26 M101 Face-on spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 with five notable companion galaxies
27 NGC 3631
28 NGC 7678
29 NGC 6946
NGC 6946
NGC 6946, , is an intermediate spiral galaxy about 22 million light-years away, on the border between the constellations Cepheus and Cygnus. It was discovered by William Herschel on September 9, 1798...

30 NGC 6365 Interacting pair of galaxies, with one galaxy viewed edge-on


Integral sign spiral galaxies

These are galaxies that look like a stretched-out S shape (or like the integral sign used in calculus
Calculus
Calculus is a branch of mathematics focused on limits, functions, derivatives, integrals, and infinite series. This subject constitutes a major part of modern mathematics education. It has two major branches, differential calculus and integral calculus, which are related by the fundamental theorem...

). Some objects, such as IC 167
IC 167
IC 167 is a barred spiral galaxy in the constellation of Aries. It was first reported by Bigourdan in 1891 and included in Dreyer's first Index Catalogue.-Galaxy group information:...

, are simply ordinary spiral galaxies viewed from an unusual angle. Other objects, such as UGC 10770, are interacting pairs of galaxies with tidal tails that look similar to spiral arms.
Arp Number Common Name Notes
31 IC 167
IC 167
IC 167 is a barred spiral galaxy in the constellation of Aries. It was first reported by Bigourdan in 1891 and included in Dreyer's first Index Catalogue.-Galaxy group information:...

32 UGC 10770
33 UGC 8613
34 NGC 4615
35 UGC 212
36 UGC 8548


Spiral galaxies with low surface brightness companions

Many of these spiral galaxies are probably interacting with the low surface brightness galaxies in the field of view. In some cases, however, it may be difficult to determine whether the companion is physically near the spiral galaxy or whether the companion is a foreground/background source or a source on the edge of the spiral galaxy.
Arp Number Common Name Notes
37 M77
Messier 77
Messier 77 is a barred spiral galaxy about 47 million light-years away in the constellation Cetus. Messier 77 is an active galaxy with an Active Galactic Nucleus , which is obscured from view by astronomical dust at visible wavelengths...

38 NGC 6412
39 NGC 1347
40 IC 4271
41 NGC 1232
NGC 1232
NGC 1232 is an intermediate spiral galaxy about 60 million light-years away in the constellation Eridanus.It is dominated by millions of bright stars and dark dust, in spiral arms rotating about the center. Open clusters containing bright blue stars are sprinkled along these spiral arms, with dark...

42 NGC 5829
NGC 5829
NGC 5829 is a galaxy in the constellation Boötes. Together with IC 4526, it forms galaxy group Arp 42. Also, it is one of 5 members of galaxy group Hickson 73 .-References:* *...

43 IC 607
44 IC 609
45 Arp 45 Galaxy triplet
46 UGC 12665
47 Arp 47
Arp 47
The designation Arp 47 represents two interacting galaxies, in the constellation Puppis:-References:*...

48 Arp 48


Spiral galaxies with small high surface brightness companions

Again, many of these spiral galaxies are probably interacting with companion galaxies, although some of the identified companion galaxies may be foreground/background sources or even bright star clusters within the individual galaxies.
Arp Number Common Name Notes
49 NGC 5665
NGC 5665
-References:***...

50 IC 1520
51 Arp 51
52 Arp 52
53 NGC 3290
54 Arp 54
55 UGC 4881
56 UGC 1432
UGC 1432
UGC 1432 or Arp 56 is a 15th magnitude spiral galaxy approximately 360 million light years distant in the constellation Aries. It is around 100 thousand light years across, similar in size to the Milky Way Galaxy. Arp 56 is characterised by the presence of a small, bright companion galaxy with...

57 Arp 57
58 UGC 4457
59 NGC 341
60 Arp 60
61 UGC 3104
62 UGC 6865
63 NGC 2944
64 UGC 9503
65 NGC 90
66 UGC 10396
67 UGC 892
68 NGC 7757
69 NGC 5579
NGC 5579
-References:* * *...

70 UGC 934
71 NGC 6045
72 NGC 5994, NGC 5996
73 IC 1222
74 Arp 74
75 NGC 702
76 M90
Messier 90
Messier 90 is a spiral galaxy about 60 million light-years away in the constellation Virgo. It was discovered by Charles Messier in 1781.- Membership of the Virgo Cluster :...

77 NGC 1097
NGC 1097
NGC 1097 is a barred spiral galaxy about 45 million light-years away in the constellation Fornax. As of 2006, three supernovae have been observed in NGC 1097....

78 NGC 772
NGC 772
NGC 772 is an unbarred spiral galaxy approximately 130 million light-years away in the constellation Aries. It is notable for possessing a single elongated outer spiral arm, which has likely arisen due to tidal interactions with nearby galaxies...



Spiral galaxies with large high surface brightness companions

Galaxies in this category are almost always clearly interacting sources. The most famous of these objects is the Whirlpool galaxy (M51; Arp 85), which is composed of a spiral galaxy NGC 5194 that is interacting with a smaller elliptical galaxy NGC 5195
NGC 5195
NGC 5195 is a dwarf galaxy that is interacting with the Whirlpool Galaxy . Both galaxies are located approximately 25 million light-years away in the constellation Canes Venatici...

. The interaction has distorted the shape of both galaxies; the spiral arm pattern has been enhanced in the larger spiral galaxy, and a bridge of stars and gas has formed between the two galaxies. Many of the other galaxies in this category are also connected by bridges.
Arp Number Common Name Notes
79 NGC 5490C
80 NGC 2633
81 NGC 6621, UGC 11175, NGC 6622
82 NGC 2535
NGC 2535
NGC 2535 is an unbarred spiral galaxy in the constellation Cancer that is interacting with NGC 2536. The two galaxies are listed together in the Atlas of Peculiar Galaxies as an example of a spiral galaxy with a high surface brightness companion....

, NGC 2536
NGC 2536
NGC 2536 is a barred spiral galaxy in the constellation Cancer that is interacting with NGC 2536. The two galaxies are listed together in the Atlas of Peculiar Galaxies as an example of a spiral galaxy with a high surface brightness companion....

83 NGC 2799, NGC 3800
84 NGC 5394, NGC 5395
85 The Whirlpool Galaxy (M51)
86 NGC 7752, NGC 7753
87
Arp 87
Arp 87 is a pair of interacting galaxies NGC 3808A and NGC 3808B.It is situated about 300 million light-years from Earth in the Leo constellation.-External links:** at BadAstronomy.com...

NGC 3808A
NGC 3808A
NGC 3808A is a galaxy that is interacting with NGC 3808B, creating a pair of galaxies called Arp 87.-External links:* * *...

, NGC 3808B
NGC 3808B
NGC 3808B is a galaxy that is interacting with NGC 3808A, creating a pair of galaxies called Arp 87.-External links:* * *...

88 Arp 88
89 NGC 2648
90 NGC 5929
NGC 5929
NGC 5929 is a Seyfert galaxy in the constellation Boötes. The pair of galaxies, NGC 5929 and NGC 5930, areinteracting.-External links:*...

, NGC 5930
NGC 5930
NGC 5930 is a galaxy in the constellation Boötes. Interacting Galaxies, NGC 5930 and NGC 5929.-References:**...

91 NGC 5953, NGC 5954


Spiral galaxies with elliptical companions

Like the spiral galaxies with high surface brightness companions, most of these spiral galaxies are clearly interacting systems. Tidal tails and bridges are visible in many of the images.
Arp Number Common Name Notes
92 NGC7603
93 NGC 7284, NGC 7285
94 NGC 3226
NGC 3226
NGC 3226 is a dwarf elliptical galaxy that is interacting with the spiral galaxy NGC 3227. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies...

, NGC 3227
NGC 3227
NGC 3227 is a spiral galaxy that is interacting with the dwarf elliptical galaxy NGC 3226. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies...

95 IC 4461, IC 4462
IC 4462
-References:* *...

96 Arp 96
97 UGC 7085A
98 Arp 98
99 NGC 7547, NGC 7549, NGC 7550 Galaxy triplet
100 IC 18, IC 19
101 UGC 10164, UGC 10169


Elliptical galaxies connected to spiral galaxies

These objects are very similar to the spiral galaxies with elliptical companions. All of the galaxies have features such as tidal tails and tidal bridges that have formed through gravitational interaction.
Arp Number Common Name Notes
102 Arp 102
103 UGC 10586 Galaxy triplet
104
Arp 104
Arp 104, also known as Keenan's system, is entry 104 in Halton Arp's Atlas of Peculiar Galaxies catalog for spiral galaxy NGC 5216 and globular galaxy NGC 5218. The two galaxies are joined by a bridge of galactic material spanning 22 000 light years.In 1790 William Herschel discovered the...

NGC 5216, NGC 5218
105 NGC 3561
NGC 3561
NGC 3561 is a pair of interacting galaxies NGC 3561A and NGC 3561B within the galaxy cluster Abell 1185. Its common name is "the Guitar" and contains a small tidal dwarf galaxy known as Ambartsumian's Knot.-External links:*...

106 NGC 4211
107 UGC 5984
108 Arp 108


Elliptical galaxies repelling spiral arms

Based on the description of these objects, it appears that Arp originally thought that the elliptical galaxies were pushing away spiral arms in companion galaxies. However, the tidal spiral arms may actually look distorted because of the interaction. Some of these "repelled" spiral arms are on the opposite side of the spiral galaxy from the elliptical galaxy. Simulations have shown that such features can be formed through gravitational interactions alone; no repelling forces are needed.
Arp Number Common Name Notes
109 UGC 10053
110 Arp 110
111 Arp 111 Galaxy group
112 NGC 7805, NGC 7806


Elliptical galaxies close to and perturbing spiral galaxies

This is another category in which the majority of objects are interacting galaxies. As noted in the category name, the spiral galaxies look perturbed. Arp originally described some of the elliptical galaxies as repelling.
Arp Number Common Name Notes
113 NGC 70 Part of a group of galaxies
114 NGC 2276, NGC 2300
115 UGC 6678 Galaxy triplet
116 Messier 60
Messier 60
Messier 60 is an elliptical galaxy approximately 55 million light-years away in the constellation Virgo.-History:...

, NGC 4647
117
Arp 117
Arp 117 is a pair of galaxies in the constellation Boötes, composed of the two separate galaxies IC 983 and IC 982....

IC 982
IC 982
IC 982 is a galaxy in the constellation Boötes. It is part of the Arp 117 pair of galaxies with IC 983.-References:* * * * *...

, IC 983
IC 983
IC 983 is a galaxy in the constellation Boötes. It is part of the Arp 117 pair of galaxies with IC 982.-References:* * * *...

118 NGC 1141, NGC 1142
119 Arp 119
120 NGC 4435, NGC 4438
121 Arp 121
122 NGC 6040
123 NGC 1888, NGC 1889
124 NGC 6361
125 UGC 10491
126 UGC 1449
127 NGC 191 Actually interacting S0 galaxy and spiral galaxy
128 UGC 827
129 UGC 5146
130 IC 5378
131 Arp 131
132 Arp 132


Galaxies with Nearby Fragments

Arp Number Common Name Notes
133 NGC541
134 Messier 49
Messier 49
Messier 49 is an elliptical / lenticular galaxy about 49 million light-years away in the constellation Virgo. The galaxy was discovered by Charles Messier in 1771.-Supernovae:...

135 NGC 1023
136 NGC 5820
NGC 5820
NGC 5820 is a galaxy in the constellation Boötes. It lies near a similar massed galaxy, NGC 5821, at the same redshift.With a diameter of 7.1 million light years, it is larger than the similar-mass IC 1101.- References :***...


Material emanating from elliptical galaxies

Arp thought that the elliptical galaxies in this category were ejecting material from their nuclei. Many of the pictures could be interpreted that way. However, these objects are actually a mixture of other phenomena. For example, NGC 2914 (Arp 137) is merely a spiral galaxy with faint spiral arms, and NGC 4015 (Arp 138) is an interacting pair of galaxies where one galaxy is an edge-on spiral galaxy. Some objects, such as NGC 2444 and NGC 2445 (Arp 143), are systems that contain "ring galaxies", which are created when one galaxy (the elliptical galaxies in these examples) passes through the disk of another. This passage causes a gravitational wave in which gas first falls inward and then propagates outward to form the ring structure.
Arp Number Common Name Notes
137 NGC 2914 Spiral galaxy with faint spiral arms
138 NGC 4015 Interacting pair of galaxies
139 Arp 139 Interacting pair of galaxies
140 NGC 274, NGC 275 Interacting pair of galaxies
141 UGC 3730 Ring galaxy system
142 NGC 2936, NGC 2937, UGC 5130 Galaxy triplet
143 NGC 2444, NGC 2445 Ring galaxy system
144 NGC 7828, NGC 7829 Ring galaxy system
145 UGC 1840 Ring galaxy system


Amorphous galaxies

Galaxies in this category are referred to by Arp as galaxies that are neither spiral nor elliptical in shape. Although he does not use the term "amorphous" to describe these galaxies, it is the best description of these galaxies.

Many of these galaxies are either interacting galaxies or galaxies that are the remnants of the merger of two smaller galaxies. The interaction process will produce various tidal features, such as tidal tails and tidal bridges, that may last well after the progenitor galaxies' disks and nuclei have merged together. Although the tidal tails are described as several different visual phenomena ("counter-tails", "filaments", "loops"), they are all manifestations of the same phenomena.

Galaxies with associated rings

As noted above, these ring galaxies may have formed when a companion galaxy passed through
the ring galaxy. The interaction would produce a wave effect that would first draw matter into the center and then cause it to propagate outward in a ring.
Arp Number Common Name Notes
146 Arp 146
147 IC 298
148 Arp 148


Galaxies with jets

These are galaxies that appear to be ejecting material outwards from their nuclei. The "jets" themselves look similar to water spraying out of a hose. In the case of IC 803 (Arp 149) and NGC 7609 (Arp 150), the jets are simply part of the amorphous structure produced by the interacting galaxies. In Arp 151 and Messier 87
Messier 87
Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...

 (Arp 152), however, the jets are ionized gas that has been ejected from the environment around supermassive black holes in the galaxies' active galactic nuclei. These jets, sometimes called relativistic jet
Relativistic jet
Relativistic jets are extremely powerful jets of plasma which emerge from presumed massive objects at the centers of some active galaxies, notably radio galaxies and quasars. Their lengths can reach several thousand or even hundreds of thousands of light years...

s or radio jets, are powerful sources of synchrotron
Synchrotron
A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronised with the travelling particle beam. The proton synchrotron was originally conceived by Sir Marcus Oliphant...

 radiation, especially at radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 wavelengths.
Arp Number Common Name Notes
149 IC 803 Interacting galaxies
150 NGC 7609 Interacting galaxies
151 Arp 151 Seyfert galaxy
Seyfert galaxy
Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943...

 (contains an active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

)
152 Messier 87
Messier 87
Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...

Seyfert galaxy
Seyfert galaxy
Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943...

 (contains an active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

)


Disturbed galaxies with interior absorption

Galaxies in this category feature dark dust lanes that obscure part of the disk of the galaxy. All of these galaxies are the products of two galaxies merging together. NGC 520
NGC 520
NGC 520 is a pair of colliding spiral galaxies about 90 million light-years away in the constellation Pisces. It has a H II nucleus.-External links:*...

 (Arp 157) is one of the best examples of an intermediate-stage merger, where the two progenitor galaxies' disks have coalesced together but the nuclei have not. Centaurus A
Centaurus A
Centaurus A is a prominent galaxy in the constellation of Centaurus. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance...

 (Arp 153) and NGC 1316
NGC 1316
NGC 1316 is a lenticular galaxy about 70 million light-years away in the constellation Fornax. NGC 1316 is a radio galaxy. It is the fourth-brightest radio source in the sky .-Structure and formation:...

 (Arp 154) are both effectively elliptical galaxies with unusual dust lanes; their kinematics and structure indicate that they have undergone merging events recently. NGC 4747 (Arp 159) may be nothing more than an edge-on spiral galaxy with a significantly dark dust lanes.
Arp Number Common Name Notes
153 Centaurus A
Centaurus A
Centaurus A is a prominent galaxy in the constellation of Centaurus. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance...

Notable radio galaxy
Radio galaxy
Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy that are very luminous at radio wavelengths, with luminosities up to 1039 W between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process...

; contains an active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

)
154 NGC 1316
NGC 1316
NGC 1316 is a lenticular galaxy about 70 million light-years away in the constellation Fornax. NGC 1316 is a radio galaxy. It is the fourth-brightest radio source in the sky .-Structure and formation:...

Notable radio galaxy
Radio galaxy
Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy that are very luminous at radio wavelengths, with luminosities up to 1039 W between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process...

; contains an active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

)
155 Arp 155
156 UGC 5184
157 NGC 520
NGC 520
NGC 520 is a pair of colliding spiral galaxies about 90 million light-years away in the constellation Pisces. It has a H II nucleus.-External links:*...

Notable intermediate-stage merger
158 NGC 523
159 NGC 4747 Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 with dark dust lanes
160 NGC 4194
NGC 4194
NGC 4194 is pair of interacting galaxies in the constellation Ursa Major....

Also known as the Medusa Galaxy Merger


Galaxies with diffuse filaments

The filaments in these objects may represent tidal tails from galaxy interactions. Many of the galaxies are the remnants of the mergers of two spiral galaxies to form a single elliptical galaxy. However, NGC 3414 (Arp 162) appears to be merely an unusual S0 galaxy with a very small disk relative to its bulge size. NGC 4670 (Arp 163) is a blue compact dwarf galaxy
Blue compact dwarf galaxy
In astronomy, a blue compact dwarf galaxy is a small galaxy which contains large clusters of young, hot, massive stars. These stars cause the galaxy to appear blue in color. Since they exist mostly in clusters, blue compact dwarf galaxies don't have an exact uniform shape...

 with extremely strong star formation activity
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...

; it is clearly too small to be the merger remnant of two spiral galaxies like the other merger remnants in this sample, although it may have been involved in a much smaller interaction.
Arp Number Common Name Notes
161 UGC 6665
162 NGC 3414 S0 galaxy
163 NGC 4670 Blue compact dwarf galaxy
Blue compact dwarf galaxy
In astronomy, a blue compact dwarf galaxy is a small galaxy which contains large clusters of young, hot, massive stars. These stars cause the galaxy to appear blue in color. Since they exist mostly in clusters, blue compact dwarf galaxies don't have an exact uniform shape...

164 NGC 455
165 NGC 2418
166 NGC 750, NGC 751


Galaxies with diffuse counter-tails

All of these objects are galaxies involved in gravitational interactions. These counter-tails are tidal features caused by the gravitational interactions between two galaxies, just like similar features described in the Arp catalog. Messier 32
Messier 32
Messier 32 is a dwarf elliptical galaxy about 2.65 million light-years away in the constellation Andromeda. M32 is a satellite galaxy of the famous Andromeda Galaxy and was discovered by Le Gentil in 1749. M32 measures only 6.5 ± 0.2 kly in diameter at the widest point...

 (Arp 168), a dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

 interacting with the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...

, is included in this category (although the "diffuse counter-tail" is very difficult to see in Arp's photograph).
Arp Number Common Name Notes
167 NGC 2672, NGC 2673
168 Messier 32
Messier 32
Messier 32 is a dwarf elliptical galaxy about 2.65 million light-years away in the constellation Andromeda. M32 is a satellite galaxy of the famous Andromeda Galaxy and was discovered by Le Gentil in 1749. M32 measures only 6.5 ± 0.2 kly in diameter at the widest point...

Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

 interacting with Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...

169 NGC 7236, NGC 7237, NGC 7237C Galaxy triplet
170 NGC 7578
171 NGC 5718, IC 1042
172 IC 1178, IC 1181


Galaxies with narrow counter-tails

This is another category containing galaxies with tidal tails produced by gravitational interactions. These tidal tails are narrower and better defined than the tidal tails in objects 167-172.
Arp Number Common Name Notes
173 UGC 9561
UGC 9561
UGC 9561 is a galaxy in the constellation Boötes. It is part of the Arp 173 pair of galaxies, with MCG+02-38-020.-References:* * * * * *...

174 NGC 3068
175 IC 3481, IC 3481A, IC 3483 Galaxy triplet
176 NGC 4933 Galaxy triplet
177 Arp 177
Arp 177
Arp 177, APG 177 or VV 840 is a group of galaxies in the constellation Boötes.It is composed of:* MCG 4-35-17* MCG 4-35-16- References :*...

178
Arp 178
Arp 178 is a triplet of galaxies, in the constellation Boötes: * NGC 5613* NGC 5614* NGC 5615...

NGC 5613
NGC 5613
NGC 5613 is galaxy in the constellation Boötes. It is part of the Arp 178 set of interacting galaxies, with NGC 5615 and NGC 5614.-References:* * *...

, NGC 5614
NGC 5614
NGC 5614 is galaxy in the constellation Boötes. It is part of the Arp 178 triplet of interacting galaxies with NGC 5613 and NGC 5615.-References:* * * *...

, NGC 5615
NGC 5615
NGC 5615 is a galaxy in the constellation Boötes. It is part of the Arp 178 triplet of interacting galaxies with NGC 5614 and NGC 5613.-References:***...

Galaxy triplet


Galaxies with narrow filaments

This category contains a mixture of different types of objects. Like the galaxies with diffuse filaments or galaxies with counter-tails, some of the galaxies in this category have been involved in interactions, and the filaments are tidal features created by those interactions. Other sources, however, are simply individual spiral galaxies with faint spiral arms that are described as "filaments" by Arp.
Arp Number Common Name Notes
179 Arp 179
180 Arp 180 Interacting galaxy pair
181 NGC 3212, NGC 3215 Interacting galaxy pair
182 NGC 7674, NGC 7674A Interacting galaxy pair
183 UGC 8560 Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

184 NGC 1961 Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

185 NGC 6217 Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

186 NGC 1614 Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 involved in recent interaction
187 Arp 187
Arp 187
Arp 187 is a radio galaxy located in the constellation Eridanus. It is an interacting galaxy pair .-External links:*...

188 Tadpole Galaxy
Tadpole Galaxy
The Tadpole Galaxy is a disrupted barred spiral galaxy located 400 million light years from Earth toward the northern constellation Draco. Its most dramatic features are a trail of stars about 280 thousand light-years long and massive, bright blue star clusters.It is hypothesized that a more...

Galaxy involved in recent interaction
189 NGC 4651 Tidal star streams
190 UGC 2320
UGC 2320
-References:* * * *...

Interacting galaxy pair
191 UGC 6175 Interacting galaxy pair
192 NGC 3303 Interacting galaxy pair
193 IC 883 Merger remnant


Galaxies with material ejected from nuclei

The ejecta in many of these objects appear to be tidal features created by gravitational interactions. In some cases (such as for NGC 5544
NGC 5544
NGC 5544 is galaxy in the constellation Boötes. Interacting galaxies, NGC 5544 and NGC 5545.-References:***...

 and NGC 5545
NGC 5545
NGC 5545 is a galaxy in the constellation Boötes. It is a single galaxy in pair of galaxies.-References:* * *...

 in Arp 199), the "ejecta" are clearly a spiral galaxy viewed edge-on that happens to line up with another galaxy's nucleus.

Almost all of the objects in this category are interacting or have recently undergone interactions. NGC 3712 (Arp 203) is an exception; it is merely a low surface brightness spiral galaxy.
Arp Number Common Name Notes
194 UGC 6945 Interacting galaxy pair
195 UGC 4653 Interacting galaxy triplet
196 Arp 196 Interacting galaxy pair
197 UGC 6503, IC 701 Interacting galaxy pair
198 UGC 6073 Interacting galaxy pair
199 NGC 5544
NGC 5544
NGC 5544 is galaxy in the constellation Boötes. Interacting galaxies, NGC 5544 and NGC 5545.-References:***...

, NGC 5545
NGC 5545
NGC 5545 is a galaxy in the constellation Boötes. It is a single galaxy in pair of galaxies.-References:* * *...

Interacting galaxy pair
200 NGC 1134
NGC 1134
-References:* *...

Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 interacting with low surface brightness galaxy
201 UGC 224 Interacting galaxy pair
202 NGC 2719, NGC 2719A Interacting galaxy pair
203 NGC 3712 Low surface brightness spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

204 UGC 8454 Interacting galaxy pair
205 NGC 3448 Merger remnant
206 UGC 5983, NGC 3432 Interacting galaxy pair
207 UGC 5050 Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 interacting with dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

208 Arp 208 Interacting galaxy pair


Galaxies with irregularities, absorption, and resolution

Galaxies in this category have either irregular structures (irregularities), notable dust lanes (absorption), or a grainy appearance (resolution). This category contains a mix of interacting galaxies distorted by tidal interactions, nearby dwarf irregular galaxies, and spiral galaxies with unusual large amounts of gas.
Arp Number Common Name Notes
209 NGC 6052 Interacting galaxy pair
210 NGC 1569
NGC 1569
NGC 1569 is a dwarf irregular galaxy in Camelopardalis. While this faint galaxy is not a popular amateur astronomy target, it is well studied by professional astronomers, who are interested in the history of star formation within the galaxy. The galaxy is relatively nearby. Consequently, the...

Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

211 UGCA 290 Interacting dwarf galaxies
212 NGC 7625 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

213 IC 356 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

214 NGC 3718 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...



Galaxies with adjacent loops

These adjacent loops are another manifestation of the structures formed by gravitational interactions between galaxies. Some of these sources consist of galaxies that have nearly completed the merger process; the "adjacent loops" are merely the remnants of the interaction. Among the objects in this category is Arp 220
Arp 220
Arp 220 is the result of a collision between two galaxies which are now in the process of merging. Located 250 million light-years away in the constellation Serpens, it is the 220th object in Halton Arp's Atlas of Peculiar Galaxies.-Features:...

, one of the best-studied ultraluminous infrared galaxies in the sky.
Arp Number Common Name Notes
215 NGC 2782 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

216 NGC 7679, NGC 7682 Interacting galaxy pair
217 NGC 3310
NGC 3310
NGC 3310 is a grand design spiral galaxy in the constellation Ursa Major. It is a starburst galaxy and its likely that NGC 3310 collided with one of its satellite galaxies about 100 million years ago, triggering widespread star formation...

Notable nearby starburst
Starburst (astronomy)
In astronomy, starburst is a generic term to describe a region of space with an abnormally high rate of star formation. It is reserved for truly unusual objects....

; merger remnant
218 Arp 218 Interacting galaxy pair
219 UGC 2812 Galaxy in interaction
220 Arp 220
Arp 220
Arp 220 is the result of a collision between two galaxies which are now in the process of merging. Located 250 million light-years away in the constellation Serpens, it is the 220th object in Halton Arp's Atlas of Peculiar Galaxies.-Features:...

Merger remnant; notable ultraluminous infrared galaxy


Galaxies with amorphous spiral arms

Many of these galaxies are merger remnants. The "amorphous spiral arms" are the tidal debris that remains after the collision.
Arp Number Common Name Notes
221 Arp 221 Interacting galaxy triplet
222 NGC 7727 Merger remnant
223 NGC 7585 Recent inequal-mass merger
224 NGC 3921 Merger remnant
225 NGC 2655 Recent inequal-mass merger
226 The Atoms for Peace Galaxy (NGC 7252
NGC 7252
NGC 7252 is a peculiar galaxy resulting from an interaction between two galaxies that started a billion years ago. It is located 220 million light years away in the constellation Aquarius...

)
Merger remnant


Galaxies with concentric rings

These are galaxies with shell-like structures. Some shell structures have been identified as the results of recent mergers. In other cases, however, the shell structure may represent the outer disk of an S0 galaxy. In some complicated cases, the galaxy with the rings or shells is an S0 galaxy interacting with another galaxy; the origins of the shells in such systems can be difficult to determine.
Arp Number Common Name Notes
227 NGC 470, NGC 474
NGC 474
NGC 474 is an elliptical galaxy about 100 million light years distant in the constellation pisces. This large galaxy is known to possess tidal tails, although their origins remain unknown.-Further reading:...

Interacting galaxy pair with one S0 galaxy
228 IC 162 S0 galaxy
229 NGC 507, NGC 508 Interacting galaxy pair including one S0 galaxy and one elliptical galaxy
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...

230 IC 51 Peculiar S0 galaxy; possible merger remnant
231 IC 1575
232 NGC 2911 Peculiar S0 galaxy


Galaxies with the appearance of fission

Although the description of the objects in this category implies that the galaxies are separating apart, most of these galaxies are merging together. Many of the objects have very pronounced tidal tails and bridges that have formed as a consequence of the interaction. Most objects are in the early stages of the merging process, where the galaxies still appear to have distinct nuclei and distinct (albeit distorted) disks. Among the most notable galaxies in this category are the Antennae Galaxies
Antennae Galaxies
The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a phase of starburst. They were discovered by William Herschel in 1785...

 (NGC 4038 and NGC 4039, Arp 244) and the Mice Galaxies
Mice Galaxies
NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years away, they are presently in the process of colliding and merging...

 (NGC 4676, Arp 242).

However, not all of these objects are interacting galaxies. A few of these galaxies are simply nearby dwarf galaxies with irregular structure.
Arp Number Common Name Notes
233 UGC 5720 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

234 NGC 3738 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

235 NGC 14 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

236 IC 1623 Interacting galaxy pair
237 UGC 5044 Interacting galaxy pair
238 UGC 8335 Interacting galaxy pair
239 NGC 5278, NGC 5279 Interacting galaxy pair
240
Arp 240
Arp 240 applies to two galaxies in a galaxy pair:*NGC 5257*NGC 5258...

NGC 5257
NGC 5257
NGC 5257 is a spiral galaxy located in the constellation Virgo. The galaxy is notably interacting with the spiral galaxy NGC 5258. The two galaxies are listed together as Arp 240 in the Atlas of Peculiar Galaxies. Both galaxies are distorted by the gravitational interaction, and both are...

, NGC 5258
NGC 5258
NGC 5258 is a spiral galaxy located in the constellation Virgo. The galaxy is notably interacting with the spiral galaxy NGC 5257. The two galaxies are listed together as Arp 240 in the Atlas of Peculiar Galaxies. Both galaxies are distorted by the gravitational interaction, and both are...

Interacting galaxy pair
241 UGC 9425
UGC 9425
-References:* *...

Interacting galaxy pair
242 Mice Galaxies
Mice Galaxies
NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years away, they are presently in the process of colliding and merging...

 (NGC 4676)
Interacting galaxy pair
243 NGC 2623 Interacting galaxy triplet
244 Antennae Galaxies
Antennae Galaxies
The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a phase of starburst. They were discovered by William Herschel in 1785...

 (NGC 4038, NGC 4039)
Interacting galaxy pair
245 NGC 2992, NGC 2993 Interacting galaxy pair
246 NGC 7837, NGC 7838 Interacting galaxy pair
247 UGC 4383 Interacting galaxy pair
248 Arp 248 Interacting galaxy triplet
249 UGC 12891 Interacting galaxy pair
250 Arp 250
251 Arp 251 Interacting galaxy triplet
252 Arp 252 Interacting galaxy pair
253 UGCA 173, UGCA 174 Interacting galaxy pair
254 NGC 5917 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

255 UGC 5304 Interacting galaxy pair
256 Arp 256 Interacting galaxy pair


Galaxies with irregular clumps

These are objects that appear to be a series of irregular clumps with no coherent structure. Many of these objects are simply nearby dwarf galaxies. Some of these objects are interacting galaxies, while others are small groups of galaxies. In both cases, many of the constituent galaxies are irregular galaxies. The superposition of two or more such irregular galaxies can easily look like a single larger irregular galaxy, which is why the Atlas of Peculiar Galaxies (and other catalogs) often classify these pairs and groups as single objects.
Arp Number Common Name Notes
257 UGC 4836 Interacting galaxy pair
258 UGC 2140
UGC 2140
-References:* *...

Galaxy group
259 NGC 1741 Galaxy group
260 UGC 7230 Interacting galaxy pair
261 Arp 261 Galaxy group
262 Arp 262 Interacting galaxy pair
263 NGC 3239 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

264 NGC 3104 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

265 IC 3862 Interacting galaxy pair
266 NGC 4861 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

267 UGC 5746 Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...

268 Holmberg II Dwarf galaxy
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...



Double and multiple galaxies

Arp originally referred to these galaxies as "double galaxies", but many of these sources are more than two galaxies. Some of the objects consist of interacting galaxies, whereas other sources are actually groups of galaxies. The difference is that interacting galaxies will be distorted, whereas galaxies in groups are simply gravitationally bound to each other but not necessarily close enough to each other to induce major structural changes.

Galaxies with connected arms

All of these galaxies are interacting pairs of galaxies except for NGC 5679 (Arp 274), which may be an interacting galaxy triplet.
The connected arms described here are tidal bridge features that form between interacting galaxies. These bridges form early during galaxy interactions.
Arp Number Common Name Notes
269 NGC 4485, NGC 4490 Interacting galaxy pair
270 NGC 3395, NGC 3396 Interacting galaxy pair
271
Arp 271
NGC 5426 and NGC 5427 are two spiral galaxies of similar sizes engaged in a dramatic dance. It is not certain that this interaction will end in a collision and ultimately a merging of the two galaxies, although the galaxies have already been affected...

NGC 5426, NGC 5427 Interacting galaxy pair
272
Arp 272
Arp 272 is a pair of colliding galaxies consisting of the two spiral galaxies NGC 6050 and IC 1179 and lies around 450 million light years from Earth in the constellation of Hercules...

NGC 6050, IC 1179 Interacting galaxy pair
273
Arp 273
Arp 273 is a group of interacting galaxies, lying 300 million light years away in the constellation Andromeda. It was first described in the Atlas of Peculiar Galaxies, compiled by Halton Arp in 1966. The larger of the spiral galaxies, known as UGC 1810, is about five times heavier...

UGC 1810, UGC 1813 Interacting galaxy pair
274 NGC 5679 Interacting galaxy triplet


Interacting galaxies

Unlike many of the objects listed in the amorphous galaxies section, the interacting galaxies that comprise these objects are still distinguishable from each other.
Arp Number Common Name Notes
275 NGC 2881 Interacting galaxy pair
276
Arp 276
Arp 276 is a pair of interacting galaxies NGC 935 and IC 1801 within the Aries constellation. NGC 935 is the northern member of the pair and IC 1801 is the southern.-References:* *...

NGC 935, IC 1801 Interacting galaxy pair
277 NGC 4809, NGC 4810 Interacting galaxy pair
278 NGC 7253 Interacting galaxy pair
279 NGC 1253, NGC 1253A Interacting galaxy pair
280 NGC 3769, NGC 3769A Interacting galaxy pair


Galaxies with infall and attraction

This category contains an odd mixture of objects. Two of the objects are edge-on disk galaxies with smaller companion galaxies nearby. Two of the objects are connected by tidal bridges. The last two objects may simply be interacting with each other over long distance.
Arp Number Common Name Notes
281 NGC 4627
NGC 4627
NGC 4627 is a dwarf elliptical galaxy in the constellation Canes Venatici....

, NGC 4631
NGC 4631
NGC 4631 is an edge-on spiral galaxy in the constellation Canes Venatici. This galaxy's slightly distorted wedge shape gives it the appearance of a herring or a whale, whence its nickname...

Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 with companion dwarf elliptical galaxy
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...

282 NGC 169, NGC 169A Spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

 with smaller companion galaxy
283 NGC 2798, NGC 2799 Interacting galaxy pair
284 NGC 7714
NGC 7714
NGC 7714 spiral galaxy in the constellation Pisces. It was discovered by John Herschel on 18 September 1830.NGC 7714 and NGC 7715 are interacting galaxies. The pair are also known as Arp 284. NGC 7714 appears to be a highly distorted spiral, possibly a barred spiral galaxy...

, NGC 7715
Interacting galaxy pair
285 NGC 2854, NGC 2856 Galaxy pair
286 NGC 5560, NGC 5566, NGC 5569 Interacting galaxy triplet


Galaxies with wind effects

Although included in the double galaxies category, many of these objects are individual galaxies. The "wind effects" refer to the appearance, not the actual detection of high-velocity gas (such as is found in M82
Messier 82
Messier 82 is the prototype nearby starburst galaxy about 12 million light-years away in the constellation Ursa Major...

). In some cases, the appearance may be the result of interaction. In other cases, particularly NGC 3981 (Arp 289), the faint, extended emission may be related to the intrinsic nature of the galaxy itself and not interactions with other objects.
Arp Number Common Name Notes
287 NGC 2735, NGC 2735A Galaxy pair
288 NGC 5221, NGC 5222 Galaxy triplet
289 NGC 3981 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

290 IC 195
IC 195
-References:* *...

, IC 196
Interacting galaxy pair
291 UGC 5832 Irregular galaxy
Irregular galaxy
An irregular galaxy is a galaxy that does not have a distinct regular shape, like a spiral or an elliptical galaxy. The shape of an irregular galaxy is uncommon – they do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a...

292 IC 575 Peculiar spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...

293 NGC 6285, NGC 6286 Interacting galaxy pair


Double or multiple galaxies with long filaments

The long filaments in these systems are probably tidal tails or bridges that have been produced as the result of the gravitational interaction between the galaxies.
Arp Number Common Name Notes
294 NGC 3786, NGC 3788 Interacting galaxy pair
295 Arp 295 Interacting galaxy pair
296 Arp 296
297 Arp 297
Arp 297
Arp 297 is a quartet of galaxies, in the constellation Boötes:* NGC 5752* NGC 5753* NGC 5754* NGC 5755...

Interacting galaxies within a galaxy group


Unclassified objects

Arp did not give a subclassification for objects 298-310 in his atlas. These objects are mostly interacting galaxy pairs.
Arp Number Common Name Description
298 NGC 7469, IC 5283 Galaxy pair
299 Arp 299
Arp 299
Arp 299 is a set of galaxies approximately 134 million light-years away in the constellation Ursa Major.Both of the galaxies involved in the collision are barred irregular galaxies....

Galaxy triplet
300 Arp 300 Galaxy group
301 UGC 6204, UGC 6207 Galaxy pair
302 UGC 9618
UGC 9618
UGC 9618 is a galaxy in the constellation Boötes. UGC 9618, also known as VV 340 or Arp 302 consists of a pair of very gas-rich spiral galaxies in their early stages of interaction. An enormous amount of infrared light is radiated by the gas from massive stars that are forming at a rate similar to...

Galaxy pair
303 IC 563, IC 564 Galaxy pair
304 NGC 1241, NGC 1242 Galaxy pair
305 NGC 4016, NGC 4017 Galaxy pair
306 Arp 306 Galaxy group with two galaxy pairs
307 NGC 2872, NGC 2874 Galaxy pair
308 NGC 545, NGC 547 Galaxy pair
309 NGC 942, NGC 943 Galaxy pair
310 IC 1259 Galaxy pair


Groups of galaxies

Arp Number Common Name Description
311 IC 1258 and Companions
312 MCG +08-31-004
313 NGC 3994 + NGC 3995
314 MCG -03-58-009 + MCG -03-58-010 + MCG -03-58-011
315 NGC 2830 + NGC 2831 + NGC 2832
316 NGC 3193
317 Leo Triplet
Leo Triplet
The Leo Triplet is a small group of galaxies about 35 million light-years away in the constellation Leo. This galaxy group consists of the spiral galaxies M65, the M66, and the NGC 3628.-Members:...

318 NGC 833 and companions
319 Stephan's Quintet
Stephan's Quintet
Stephan's Quintet in the constellation Pegasus is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group was discovered by Édouard Stephan in 1877 at Marseilles Observatory....

320 Copeland's Septet
321 Hickson 40 A-E


Chains of galaxies

Arp Number Common Name Description
322 UGC 6527
323 Hickson 98 A-D
324 UGC 10143
325 ESO601-G018A+B and MCG -04-52-014
326 UGC 8610
327 NGC 1875; Hickson 34 A-D
328 UGC 9532; Hickson 72
329 UGC 6514
330 I Zw 167; MCG +09-27-094
331 NGC 379 and companions (Pisces Cloud)
332 NGC 1228


Miscellaneous

Arp Number Common Name Description
333 NGC 1024
334 UGC 8498
335 NGC 3509
336 NGC 2685
337 Messier 82
Messier 82
Messier 82 is the prototype nearby starburst galaxy about 12 million light-years away in the constellation Ursa Major...

338 PGC 3094767


Brightest Arp galaxies for amateur astronomers

Maynard Pittendreigh
Maynard Pittendreigh
The Rev. Dr. W. Maynard Pittendreigh is an astronomer, writer and an ordained minister in the Presbyterian Church . As a minister, he has been a pioneer and leader in a movement toward multi-cultural/racial congregations, and in developing early Internet-based ministries.William Maynard...

, an amateur astronomer and occasional writer, has compiled a list of the brightest Arp Galaxies that are most easily viewed by typical amateur astronomers. The galaxies on the list can be observed visually and do not require special photographic or imaging equipment. These include:

  • Arp 26, also known as M 101
  • Arp 37, also known as M 77
  • Arp 76, also known as M 90
  • Arp 77
  • Arp 85, also known as M 51

  • Arp 116, also known as M 60
  • Arp 120
  • Arp 152, also known as M 87
  • Arp 153
  • Arp 168, also known as M 32

  • Arp 244
  • Arp 269
  • Arp 270
  • Arp 271
    Arp 271
    NGC 5426 and NGC 5427 are two spiral galaxies of similar sizes engaged in a dramatic dance. It is not certain that this interaction will end in a collision and ultimately a merging of the two galaxies, although the galaxies have already been affected...

  • Arp 281

  • Arp 286
  • Arp 317, also known as M 65
  • Arp 313
  • Arp 337, also known as M 82


See also

  • Index Catalogue
    Index Catalogue
    The Index Catalogue —also known as the Index Catalogue of Nebulae, the Index Catalogue of Nebulae and Clusters of Stars, IC I, or IC II— is a catalogue of galaxies, nebulae and star clusters that serves as a supplement to the New General Catalogue...

     (IC)
  • Messier object
    Messier object
    The Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets...

     (M)
  • New General Catalogue
    New General Catalogue
    The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...

     (NGC)
  • Uppsala General Catalogue
    Uppsala General Catalogue
    The Uppsala General Catalogue of Galaxies is a catalogue of 12921 galaxies visible from the northern hemisphere. It was published the first time in 1973....

    (UGC)

Further reading

  • J. Kanipe, D. Webb The Arp Atlas of Peculiar Galaxies, A Chronicle and Observer's Guide, Willmann-Bell Inc. (2006) ISBN 978-0-943396-76-7

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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