Atlas of Peculiar Galaxies

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The Antennae Galaxies (Arp 244)
Colliding spiral galaxy pair NGC 3808A and NGC 3808B (Arp 87).
NGC 6621/NGC 6622 (Arp 81), a pair of spiral galaxies 100 million years after their colliding.
IC 883 (Arp 193), remnant of two galaxies' merger.
Arp 147, an interacting pair of ring galaxies.

The Atlas of Peculiar Galaxies is a catalog of peculiar galaxies produced by Halton Arp. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology.[1]

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 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.

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).

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, and the Antennae Galaxies (NGC 4038/NGC 4039, or Arp 244). A few of the galaxies are simply dwarf galaxies that do not have enough mass to produce enough gravity to allow the galaxies to form any cohesive structure. NGC 1569 (Arp 210) 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) and Centaurus A (Arp 153).

Contents

Notable Arp galaxies[edit]

The Mice Galaxies (NGC 4676; Arp 242). These two galaxies both have tidal tails that form as a consequence of the galaxies' gravitational interaction. The galaxies are also connected by a tidal bridge, another feature formed by the gravitational interaction.
Merging galaxy pair "The Grasshopper" (alias UGC 4881, FUDGE, Arp 55).
Arp Number Name Magnitude Notes
26 Pinwheel Galaxy (M101) +7.5 spiral galaxy
37 Messier 77 +8.9 radio galaxy
41 NGC 1232 +9.8 spiral galaxy
76 Messier 90 +9.5 spiral galaxy
77 NGC 1097 +9.5 galaxy interacting with its satellite
85 Whirlpool Galaxy (M51) +8.4 galaxy interacting with its satellite
116 Messier 60 +8.8 colliding galaxies
152 Virgo A (M87) +8.6 elliptical galaxy
153 Centaurus A (NGC 5128) +6.6 radio galaxy in a collision?
188 Tadpole Galaxy +14.4 galaxy finishing merging
242 Mice Galaxies +14.7 colliding galaxies
244 Antennae Galaxies +10.3 colliding galaxies
317 Messier 65 +9.2 spiral galaxy
319 NGC 7320 +15 galaxy in colliding group
337 Cigar Galaxy (M82) +8.6 starburst galaxy

List of galaxies in the catalog[edit]

Spiral galaxies[edit]

Low surface brightness galaxies[edit]

Ultraviolet image of NGC 2537 (Arp 6)

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).[2]

Arp Number Common Name Notes
1 NGC 2857 Sc spiral galaxy[2]
2 UGC 10310
3 Arp 3
4 Arp 4
5 NGC 3664
6 NGC 2537

Galaxies with split arms[edit]

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

Galaxies with detached segments[edit]

M66 (Arp 16)

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
15 NGC 7393
16 M66
17 UGC 3972
18 NGC 4088

Three-armed spiral galaxies[edit]

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
20 UGC 3014
21 Arp 21

One-armed spiral galaxies[edit]

Ultraviolet image NGC 4618 (Arp 23)

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
23 NGC 4618 Interacting with NGC 4625[3]
24 NGC 3445

Spiral galaxies with one heavy arm[edit]

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 and NGC 6946) 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.[4]

Arp Number Common Name Notes
25 NGC 2276
26 M101 Face-on spiral galaxy with five notable companion galaxies[3]
27 NGC 3631
28 NGC 7678
29 NGC 6946
30 NGC 6365 Interacting pair of galaxies, with one galaxy viewed edge-on[4]

Integral sign spiral galaxies[edit]

These are galaxies that look like a stretched-out S shape (or like the integral sign used in calculus). Some objects, such as IC 167,[5] 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.[6]

Arp Number Common Name Notes
31 IC 167
32 UGC 10770
33 UGC 8613
34 NGC 4615
35 UGC 212
36 UGC 8548

Spiral galaxies with low surface brightness companions[edit]

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
38 NGC 6412
39 NGC 1347
40 IC 4271
41 NGC 1232
42 NGC 5829
43 IC 607
44 IC 609
45 UGC 9178 Galaxy triplet[7]
46 UGC 12665
47 Arp 47
48 Arp 48

Spiral galaxies with small high surface brightness companions[edit]

Image of NGC 1097 (Arp 77) spiral galaxy

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
50 IC 1520
51 Arp 51
52 Arp 52
53 NGC 3290
54 Arp 54
55 UGC 4881
56 UGC 1432
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
70 UGC 934
71 NGC 6045
72 NGC 5994, NGC 5996
73 IC 1222
74 UGC 1626
75 NGC 702
76 M90
77 NGC 1097
78 NGC 772

Spiral galaxies with large high surface brightness companions[edit]

The Whirlpool Galaxy (M51, Arp 85). This object consists of a larger spiral galaxy interacting with an elliptical galaxy.

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. 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 2536
83 NGC 2799, NGC 3800
84 NGC 5394, NGC 5395
85 The Whirlpool Galaxy (M51)
86 NGC 7752, NGC 7753
87 NGC 3808A, NGC 3808B
88 Arp 88
89 NGC 2648
90 NGC 5929, NGC 5930
91 NGC 5953, NGC 5954

Spiral galaxies with elliptical companions[edit]

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 3227
95 IC 4461, IC 4462
96 UGC 3528
97 UGC 7085A
98 UGC 1095
99 NGC 7547, NGC 7549, NGC 7550 Galaxy triplet[8]
100 IC 18, IC 19
101 UGC 10164, UGC 10169

Elliptical and elliptical-like galaxies[edit]

Elliptical galaxies connected to spiral galaxies[edit]

Different wavelength infrared images of Arp 107 (UGC 5984).

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[9]
104 NGC 5216, NGC 5218
105 NGC 3561
106 NGC 4211
107 UGC 5984
108 Arp 108

Elliptical galaxies repelling spiral arms[edit]

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 NGC 5421 Galaxy group[10]
112 NGC 7805, NGC 7806

Elliptical galaxies close to and perturbing spiral galaxies[edit]

Galaxy pair NGC 4435 and NGC 4438 (Arp 120)
Messier 60 and NGC 4647 (Arp 116)

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[11]
114 NGC 2276, NGC 2300
115 UGC 6678 Galaxy triplet[12]
116 Messier 60, NGC 4647
117 IC 982, IC 983
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[12]
128 UGC 827
129 UGC 5146
130 IC 5378
131 Arp 131
132 Arp 132

Galaxies with Nearby Fragments[edit]

Messier 49, Arp 134
Arp Number Common Name Notes
133 NGC541
134 Messier 49
135 NGC 1023
136 NGC 5820

Material emanating from elliptical galaxies[edit]

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,[13] and NGC 4015 (Arp 138) is an interacting pair of galaxies where one galaxy is an edge-on spiral galaxy.[14] 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.[15]

NGC 2936, once a standard spiral galaxy, and NGC 2937, a smaller elliptical.[16]
Arp Number Common Name Notes
137 NGC 2914 Spiral galaxy with faint spiral arms[13]
138 NGC 4015 Interacting pair of galaxies[14]
139 Arp 139 Interacting pair of galaxies[17]
140 NGC 274, NGC 275 Interacting pair of galaxies[18]
141 UGC 3730 Ring galaxy system[19]
142 NGC 2936, NGC 2937, UGC 5130 Galaxy triplet[20]
143 NGC 2444, NGC 2445 Ring galaxy system[21]
144 NGC 7828, NGC 7829 Ring galaxy system[22]
145 UGC 1840 Ring galaxy system[23]

Amorphous galaxies[edit]

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. 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[edit]

Interacting galaxy pair Arp 148 (Mayall's Object)

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.[15]

Arp Number Common Name Notes
146 Arp 146
147 IC 298
148 Arp 148

Galaxies with jets[edit]

Giant elliptical galaxy Messier 87 with its relativistic jet (Arp 152)

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 (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.[24][25] These jets, sometimes called relativistic jets or radio jets, are powerful sources of synchrotron radiation, especially at radio wavelengths.

Arp Number Common Name Notes
149 IC 803 Interacting galaxies[26]
150 NGC 7609 Interacting galaxies[27]
151 Arp 151 Seyfert galaxy (contains an active galactic nucleus)[24]
152 Messier 87 Seyfert galaxy (contains an active galactic nucleus)[25]

Disturbed galaxies with interior absorption[edit]

Merging galaxy pair named NGC 520 (Arp 157).

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. NGC 520 (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 (Arp 153) and NGC 1316 (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.[28]

Arp Number Common Name Notes
153 Centaurus A Notable radio galaxy; contains an active galactic nucleus)[29]
154 NGC 1316 Notable radio galaxy; contains an active galactic nucleus)[29]
155 NGC 3656
156 UGC 5184
157 NGC 520 Notable intermediate-stage merger
158 NGC 523
159 NGC 4747 Spiral galaxy with dark dust lanes[28]
160 NGC 4194 Also known as the Medusa Galaxy

Galaxies with diffuse filaments[edit]

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.[3] NGC 4670 (Arp 163) is a blue compact dwarf galaxy with extremely strong star formation activity;[30] 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[3]
163 NGC 4670 Blue compact dwarf galaxy[30]
164 NGC 455
165 NGC 2418
166 NGC 750, NGC 751

Galaxies with diffuse counter-tails[edit]

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 (Arp 168), a dwarf galaxy interacting with the Andromeda Galaxy,[3] 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 Dwarf galaxy interacting with Andromeda Galaxy[3]
169 NGC 7236, NGC 7237, NGC 7237C Galaxy triplet[31]
170 NGC 7578
171 NGC 5718, IC 1042
172 IC 1178, IC 1181

Galaxies with narrow counter-tails[edit]

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
174 NGC 3068
175 IC 3481, IC 3481A, IC 3483 Galaxy triplet[32]
176 NGC 4933 Galaxy triplet[33]
177 Arp 177
178 NGC 5613, NGC 5614, NGC 5615 Galaxy triplet[34]

Galaxies with narrow filaments[edit]

NGC 1614 (Arp 186).
The Tadpole Galaxy (UGC 10214; Arp 188). The "narrow filament", which appears to be tidal feature caused by a gravitational interaction, can be seen extending across this image.

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[35]
181 NGC 3212, NGC 3215 Interacting galaxy pair[36]
182 NGC 7674, NGC 7674A Interacting galaxy pair[37]
183 UGC 8560 Spiral galaxy[38]
184 NGC 1961 Spiral galaxy[39]
185 NGC 6217 Spiral galaxy[40]
186 NGC 1614 Spiral galaxy involved in recent interaction[41]
187 Arp 187
188 Tadpole Galaxy Galaxy involved in recent interaction
189 NGC 4651 Tidal star streams[42]
190 UGC 2320 Interacting galaxy pair[43]
191 UGC 6175 Interacting galaxy pair[44]
192 NGC 3303 Interacting galaxy pair[45]
193 IC 883 Merger remnant

Galaxies with material ejected from nuclei[edit]

Arp 194. The third galaxy at the bottom of the image is actually a further object, not part of the system.

The ejecta in many of these objects appear to be tidal features created by gravitational interactions. In some cases (such as for NGC 5544 and NGC 5545 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.[46]

Arp Number Common Name Notes
194 UGC 6945 Interacting galaxy pair[47]
195 UGC 4653 Interacting galaxy triplet[48]
196 Arp 196 Interacting galaxy pair[49]
197 UGC 6503, IC 701 Interacting galaxy pair[50]
198 UGC 6073 Interacting galaxy pair[51]
199 NGC 5544, NGC 5545 Interacting galaxy pair[52]
200 NGC 1134 Spiral galaxy interacting with low surface brightness galaxy[53]
201 UGC 224 Interacting galaxy pair[54]
202 NGC 2719, NGC 2719A Interacting galaxy pair[55]
203 NGC 3712 Low surface brightness spiral galaxy[46]
204 UGC 8454 Interacting galaxy pair[56]
205 NGC 3448 Merger remnant[57]
206 UGC 5983, NGC 3432 Interacting galaxy pair[58]
207 UGC 5050 Spiral galaxy interacting with dwarf galaxy[59]
208 Arp 208 Interacting galaxy pair[60]

Galaxies with irregularities, absorption, and resolution[edit]

Starburst activity in nearby dwarf galaxy NGC 1569 (Arp 210).

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[61]
210 NGC 1569 Dwarf galaxy[62]
211 UGCA 290 Interacting dwarf galaxies[63]
212 NGC 7625 Peculiar spiral galaxy[64]
213 IC 356 Peculiar spiral galaxy[65]
214 NGC 3718 Peculiar spiral galaxy[66]

Galaxies with adjacent loops[edit]

Nearby starburst spiral galaxy NGC 3310 (Arp 217)

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, one of the best-studied ultraluminous infrared galaxies in the sky.

Arp Number Common Name Notes
215 NGC 2782 Peculiar spiral galaxy[3]
216 NGC 7679, NGC 7682 Interacting galaxy pair[67]
217 NGC 3310 Notable nearby starburst;[68] merger remnant[3]
218 Arp 218 Interacting galaxy pair[69]
219 UGC 2812 Galaxy in interaction[70]
220 IC 4553 Merger remnant; notable ultraluminous infrared galaxy

Galaxies with amorphous spiral arms[edit]

Spiral galaxy NGC 7252 (Arp 226)

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[71]
222 NGC 7727 Merger remnant[3]
223 NGC 7585 Recent inequal-mass merger[3]
224 NGC 3921 Merger remnant
225 NGC 2655 Recent inequal-mass merger
226 The Atoms for Peace Galaxy (NGC 7252) Merger remnant[3]

Galaxies with concentric rings[edit]

NGC 474, Arp 227

These are galaxies with shell-like structures. Some shell structures have been identified as the results of recent mergers.[citation needed] 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 Interacting galaxy pair with one S0 galaxy[72]
228 IC 162 S0 galaxy[73]
229 NGC 507, NGC 508 Interacting galaxy pair including one S0 galaxy and one elliptical galaxy[74]
230 IC 51 Peculiar S0 galaxy;[75] possible merger remnant
231 IC 1575
232 NGC 2911 Peculiar S0 galaxy[76]

Galaxies with the appearance of fission[edit]

Interacting pair of galaxies: Arp 238 (UGC 8335).
NGC 5257 and NGC 5258 (Arp 240), interacting pair of spiral galaxies.
Arp 256, spiral galaxy pair in the early stages of colliding and merging.

Although the description of the objects in this category implies that the galaxies are separating apart, most of these galaxies are merging. 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 (NGC 4038 and NGC 4039, Arp 244) and the Mice Galaxies (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[77]
234 NGC 3738 Dwarf galaxy[78]
235 NGC 14 Dwarf galaxy[79]
236 IC 1623 Interacting galaxy pair[80]
237 UGC 5044 Interacting galaxy pair[81]
238 UGC 8335 Interacting galaxy pair[82]
239 NGC 5278, NGC 5279 Interacting galaxy pair[83]
240 NGC 5257, NGC 5258 Interacting galaxy pair[84]
241 UGC 9425 Interacting galaxy pair[85]
242 Mice Galaxies (NGC 4676) Interacting galaxy pair[86]
243 NGC 2623 Interacting galaxy triplet[87]
244 Antennae Galaxies (NGC 4038, NGC 4039) Interacting galaxy pair[88]
245 NGC 2992, NGC 2993 Interacting galaxy pair[89]
246 NGC 7837, NGC 7838 Interacting galaxy pair[90]
247 UGC 4383 Interacting galaxy pair[91]
248 Arp 248 Interacting galaxy triplet[92]
249 UGC 12891 Interacting galaxy pair[93]
250 Arp 250
251 Arp 251 Interacting galaxy triplet[94]
252 Arp 252 Interacting galaxy pair[95]
253 UGCA 173, UGCA 174 Interacting galaxy pair[96]
254 NGC 5917 Peculiar spiral galaxy[97]
255 UGC 5304 Interacting galaxy pair[98]
256 Arp 256 Interacting galaxy pair[99]

Galaxies with irregular clumps[edit]

Interacting galaxy pair Arp 261.

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 4638 Interacting galaxy pair[100]
258 UGC 2140 Galaxy group[101]
259 NGC 1741 Galaxy group[102]
260 UGC 7230 Interacting galaxy pair[103]
261 Arp 261 Galaxy group[104]
262 UGC 12856 Interacting galaxy pair[105]
263 NGC 3239 Dwarf galaxy[106]
264 NGC 3104 Dwarf galaxy[107]
265 IC 3862 Interacting galaxy pair[108]
266 NGC 4861 Dwarf galaxy[109]
267 UGC 5746 Dwarf galaxy[110]
268 UGC 4305, Holmberg II Dwarf galaxy[111]

Double and multiple galaxies[edit]

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[edit]

Arp 272: NGC 6050 and IC 1179, interacting spiral galaxies.

All of these galaxies are interacting pairs of galaxies except for NGC 5679 (Arp 274), which may be an interacting galaxy triplet.[112] 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[113]
270 NGC 3395, NGC 3396 Interacting galaxy pair[114]
271 NGC 5426, NGC 5427 Interacting galaxy pair[115]
272 NGC 6050, IC 1179 Interacting galaxy pair[116]
273 UGC 1810, UGC 1813 Interacting galaxy pair[117]
274 NGC 5679 Interacting galaxy triplet[112]

Interacting galaxies[edit]

'The Bird' - although it also bears resemblance with a cosmic Tinker Bell - is composed of two massive spiral galaxies and a third irregular galaxy.

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[118]
276 NGC 935, IC 1801 Interacting galaxy pair[119]
277 NGC 4809, NGC 4810 Interacting galaxy pair[120]
278 NGC 7253 Interacting galaxy pair[121]
279 NGC 1253, NGC 1253A Interacting galaxy pair[122]
280 NGC 3769, NGC 3769A Interacting galaxy pair[123]

Galaxies with infall and attraction[edit]

Edge-on spiral galaxy NGC 4631 and dwarf elliptical NGC 4627 (below) comprise the Arp 281 pair

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 4631 Spiral galaxy with companion dwarf elliptical galaxy[124]
282 NGC 169, NGC 169A Spiral galaxy with smaller companion galaxy[125]
283 NGC 2798, NGC 2799 Interacting galaxy pair[126]
284 NGC 7714, NGC 7715 Interacting galaxy pair[127]
285 NGC 2854, NGC 2856 Galaxy pair[128]
286 NGC 5560, NGC 5566, NGC 5569 Interacting galaxy triplet[3][129]

Galaxies with wind effects[edit]

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). 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.[3]

Arp Number Common Name Notes
287 NGC 2735, NGC 2735A Galaxy pair[130]
288 NGC 5221, NGC 5222 Galaxy triplet[131]
289 NGC 3981 Peculiar spiral galaxy[3][132]
290 IC 195, IC 196 Interacting galaxy pair[133]
291 UGC 5832 Irregular galaxy[134]
292 IC 575 Peculiar spiral galaxy[135]
293 NGC 6285, NGC 6286 Interacting galaxy pair[136]

Double or multiple galaxies with long filaments[edit]

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[137]
295 Arp 295 Interacting galaxy pair[138]
296 Arp 296
297 Arp 297 Interacting galaxies within a galaxy group[139]

Unclassified objects[edit]

IC 694 and NGC 3690 (Arp 299), interacting galaxy pair
UGC 9618 (Arp 302), a pair of a face-on and an edge-on spiral galaxy

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[140]
299 Arp 299 Galaxy triplet[141]
300 Arp 300 Galaxy group[142]
301 UGC 6204, UGC 6207 Galaxy pair[143]
302 UGC 9618 Galaxy pair[144]
303 IC 563, IC 564 Galaxy pair[145]
304 NGC 1241, NGC 1242 Galaxy pair[146]
305 NGC 4016, NGC 4017 Galaxy pair[147]
306 UGC 1102 Galaxy group with two galaxy pairs[148]
307 NGC 2872, NGC 2874 Galaxy pair[149]
308 NGC 545, NGC 547 Galaxy pair[150]
309 NGC 942, NGC 943 Galaxy pair[151]
310 IC 1259 Galaxy pair[152]

Groups of galaxies[edit]

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
318 NGC 833 and companions
319 Stephan's Quintet
320 Copeland's Septet
321 Hickson 40 A-E

Chains of galaxies[edit]

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[edit]

Arp Number Common Name Description
333 NGC 1024
334 UGC 8498
335 NGC 3509
336 NGC 2685
337 Messier 82
338 PGC 3094767

Brightest Arp galaxies for amateur astronomers[edit]

Maynard Pittendreigh, 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 M101
  • Arp 37, also known as M77
  • Arp 76, also known as M90
  • Arp 77
  • Arp 85, also known as M51
  • Arp 116, also known as M60
  • Arp 120
  • Arp 152, also known as M87
  • Arp 153
  • Arp 168, also known as M32
  • Arp 244
  • Arp 269
  • Arp 270
  • Arp 271
  • Arp 281
  • Arp 286
  • Arp 317, also known as M65
  • Arp 313
  • Arp 337, also known as M82

See also[edit]

Further reading[edit]

  • 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

References[edit]

  • Atlas of Peculiar Galaxies courtesy of the NASA/IPAC Extragalactic Database. Retrieved on 2006-07-03, 2006-07-12, 2006-07-14, 2006-07-16, 2006-07-17, 2006-07-18, 2006-07-19, 2006-07-20, 2006-07-24, 2006-07-25, 2006-07-26, 2006-07-27, 2006-07-31, 2006-08-02, 2006-08-08, 2006-08-10, 2006-08-13.
  • NASA/IPAC Extragalactic Database General information retrieval on individual Arp objects. Retrieved on 2006-07-03, 2006-07-12, 2006-07-14, 2006-07-16, 2006-07-17, 2006-07-18, 2006-07-19, 2006-07-20, 2006-07-24, 2006-07-25, 2006-07-26, 2006-07-27, 2006-07-31, 2006-08-02, 2006-08-08, 2006-08-10, 2006-08-13.

External links[edit]

Notes[edit]

  1. ^ Arp, Halton (1966). ATLAS OF PECULIAR GALAXIES. Pasadena, California: California Institute of Technology. Retrieved 5 Jan 2010.  (webpage includes PDF link)
  2. ^ a b "NASA/IPAC Extragalactic Database". Results for NGC 2857. Retrieved 2006-07-16. 
  3. ^ a b c d e f g h i j k l m n A. Sandage, J. Bedke (1994). Carnegie Atlas of Galaxies. Washington, D.C.: Carnegie Institution of Washington. ISBN 0-87279-667-1. 
  4. ^ a b "NASA/IPAC Extragalactic Database". Results for NGC 6365. Retrieved 2006-07-12. 
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  11. ^ "NASA/IPAC Extragalactic Database". Results for NGC 70. Retrieved 2006-07-19. 
  12. ^ a b "NASA/IPAC Extragalactic Database". Results for Arp 115. Retrieved 2006-07-19. 
  13. ^ a b "NASA/IPAC Extragalactic Database". Results for NGC 2914. Retrieved 2006-07-20. 
  14. ^ a b "NASA/IPAC Extragalactic Database". Results for NGC 4015. Retrieved 2006-07-20. 
  15. ^ a b R. Lynds, A. Toomre (1976). "On the interpretation of ring galaxies : the binary ring system II Hz4". Astrophysical Journal 209: 328–388. Bibcode:1976ApJ...209..382L. doi:10.1086/154730. 
  16. ^ "Hubble spots galaxies in close encounter". ESA/Hubble Press Release. Retrieved 29 June 2013. 
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  19. ^ "NASA/IPAC Extragalactic Database". Results for Arp 141. Retrieved 2006-07-20. 
  20. ^ "NASA/IPAC Extragalactic Database". Results for Arp 142. Retrieved 2006-07-20. 
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  34. ^ "NASA/IPAC Extragalactic Database". Results for Arp 178. Retrieved 2006-07-25. 
  35. ^ "NASA/IPAC Extragalactic Database". Results for Arp 180. Retrieved 2006-07-26. 
  36. ^ "NASA/IPAC Extragalactic Database". Results for Arp 181. Retrieved 2006-07-26. 
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  39. ^ "NASA/IPAC Extragalactic Database". Results for NGC 1961. Retrieved 2006-07-26. 
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  42. ^ "NGC 4651: The Umbrella Galaxy". Astronomy Picture of the Day. Archived from the original on 17 April 2010. Retrieved 2010-04-15. 
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  45. ^ "NASA/IPAC Extragalactic Database". Results for NGC3303. Retrieved 2006-07-26. 
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  48. ^ "NASA/IPAC Extragalactic Database". Results for Arp 195. Retrieved 2006-07-27. 
  49. ^ "NASA/IPAC Extragalactic Database". Results for Arp 196. Retrieved 2006-07-27. 
  50. ^ "NASA/IPAC Extragalactic Database". Results for Arp 197. Retrieved 2006-07-27. 
  51. ^ "NASA/IPAC Extragalactic Database". Results for Arp 198. Retrieved 2006-07-27. 
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  54. ^ "NASA/IPAC Extragalactic Database". Results for Arp 201. Retrieved 2006-07-27. 
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  58. ^ "NASA/IPAC Extragalactic Database". Results for Arp 206. Retrieved 2006-07-27. 
  59. ^ "NASA/IPAC Extragalactic Database". Results for Arp 207. Retrieved 2006-07-27. 
  60. ^ "NASA/IPAC Extragalactic Database". Results for Arp 208. Retrieved 2006-07-27. 
  61. ^ "NASA/IPAC Extragalactic Database". Results for Arp 209. Retrieved 2006-07-28. 
  62. ^ "NASA/IPAC Extragalactic Database". Results for NGC 1569. Retrieved 2006-07-28. 
  63. ^ "NASA/IPAC Extragalactic Database". Results for UGCA 290. Retrieved 2006-07-28. 
  64. ^ "NASA/IPAC Extragalactic Database". Results for NGC 7625. Retrieved 2006-07-28. 
  65. ^ "NASA/IPAC Extragalactic Database". Results for IC 356. Retrieved 2006-07-28. 
  66. ^ "NASA/IPAC Extragalactic Database". Results for NGC 3718. Retrieved 2006-07-28. 
  67. ^ "NASA/IPAC Extragalactic Database". Results for Arp 216. Retrieved 2006-07-27. 
  68. ^ "NASA/IPAC Extragalactic Database". Results for NGC 3310. Retrieved 2006-07-27. 
  69. ^ "NASA/IPAC Extragalactic Database". Results for Arp 218. Retrieved 2006-07-27. 
  70. ^ "NASA/IPAC Extragalactic Database". Results for Arp 219. Retrieved 2006-07-27. 
  71. ^ "NASA/IPAC Extragalactic Database". Results for Arp 221. Retrieved 2006-07-31. 
  72. ^ "NASA/IPAC Extragalactic Database". Results for Arp 227. Retrieved 2006-07-31. 
  73. ^ "NASA/IPAC Extragalactic Database". Results for IC 162. Retrieved 2006-07-31. 
  74. ^ "NASA/IPAC Extragalactic Database". Results for Arp 229. Retrieved 2006-07-31. 
  75. ^ "NASA/IPAC Extragalactic Database". Results for IC 51. Retrieved 2006-07-31. 
  76. ^ "NASA/IPAC Extragalactic Database". Results for NGC 2911. Retrieved 2006-08-10. 
  77. ^ "NASA/IPAC Extragalactic Database". Results for UGC 5720. Retrieved 2006-08-02. 
  78. ^ "NASA/IPAC Extragalactic Database". Results for NGC 3738. Retrieved 2006-08-02. 
  79. ^ "NASA/IPAC Extragalactic Database". Results for NGC 14. Retrieved 2006-08-02. 
  80. ^ "NASA/IPAC Extragalactic Database". Results for IC 1623. Retrieved 2006-08-02. 
  81. ^ "NASA/IPAC Extragalactic Database". Results for UGC 5044. Retrieved 2006-08-02. 
  82. ^ "NASA/IPAC Extragalactic Database". Results for UGC 8355. Retrieved 2006-08-02. 
  83. ^ "NASA/IPAC Extragalactic Database". Results for Arp 239. Retrieved 2006-08-02. 
  84. ^ "NASA/IPAC Extragalactic Database". Results for Arp 240. Retrieved 2006-08-02. 
  85. ^ "NASA/IPAC Extragalactic Database". Results for UGC 9425. Retrieved 2006-08-02. 
  86. ^ "NASA/IPAC Extragalactic Database". Results for NGC 4676. Retrieved 2006-08-02. 
  87. ^ "NASA/IPAC Extragalactic Database". Results for NGC 2623. Retrieved 2006-08-02. 
  88. ^ "NASA/IPAC Extragalactic Database". Results for Arp 244. Retrieved 2006-08-02. 
  89. ^ "NASA/IPAC Extragalactic Database". Results for Arp 245. Retrieved 2006-08-02. 
  90. ^ "NASA/IPAC Extragalactic Database". Results for Arp 246. Retrieved 2006-08-02. 
  91. ^ "NASA/IPAC Extragalactic Database". Results for UGC 4383. Retrieved 2006-08-02. 
  92. ^ "NASA/IPAC Extragalactic Database". Results for Arp 248. Retrieved 2006-08-02. 
  93. ^ "NASA/IPAC Extragalactic Database". Results for UGC 12891. Retrieved 2006-08-02. 
  94. ^ "NASA/IPAC Extragalactic Database". Results for Arp 251. Retrieved 2006-08-02. 
  95. ^ "NASA/IPAC Extragalactic Database". Results for Arp 252. Retrieved 2006-08-02. 
  96. ^ "NASA/IPAC Extragalactic Database". Results for Arp 253. Retrieved 2006-08-02. 
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  101. ^ "NASA/IPAC Extragalactic Database". Results for UGC 2140. Retrieved 2006-08-07. 
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  115. ^ "NASA/IPAC Extragalactic Database". Results for Arp 271. Retrieved 2006-08-10. 
  116. ^ "NASA/IPAC Extragalactic Database". Results for UGC 10186. Retrieved 2006-08-10. 
  117. ^ "NASA/IPAC Extragalactic Database". Results for Arp 273. Retrieved 2006-08-10. 
  118. ^ "NASA/IPAC Extragalactic Database". Results for NGC 2881. Retrieved 2006-08-10. 
  119. ^ "NASA/IPAC Extragalactic Database". Results for Arp 276. Retrieved 2006-08-10. 
  120. ^ "NASA/IPAC Extragalactic Database". Results for Arp 277. Retrieved 2006-08-10. 
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  128. ^ "NASA/IPAC Extragalactic Database". Results for Arp 285. Retrieved 2006-08-10. 
  129. ^ Arp 286: Trio in Virgo, Astronomy Picture of the Day
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  136. ^ "NASA/IPAC Extragalactic Database". Results for Arp 293. Retrieved 2006-08-13. 
  137. ^ "NASA/IPAC Extragalactic Database". Results for Arp 294. Retrieved 2006-08-13. 
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  140. ^ "NASA/IPAC Extragalactic Database". Results for Arp 298. Retrieved 2006-08-21. 
  141. ^ "NASA/IPAC Extragalactic Database". Results for Arp 299. Retrieved 2006-08-21. 
  142. ^ "NASA/IPAC Extragalactic Database". Results for Arp 300. Retrieved 2006-08-21. 
  143. ^ "NASA/IPAC Extragalactic Database". Results for Arp 301. Retrieved 2006-08-21. 
  144. ^ "NASA/IPAC Extragalactic Database". Results for UGC 9618. Retrieved 2006-08-21. 
  145. ^ "NASA/IPAC Extragalactic Database". Results for Arp 303. Retrieved 2006-08-21. 
  146. ^ "NASA/IPAC Extragalactic Database". Results for Arp 304. Retrieved 2006-08-21. 
  147. ^ "NASA/IPAC Extragalactic Database". Results for Arp 305. Retrieved 2006-08-21. 
  148. ^ "NASA/IPAC Extragalactic Database". Results for Arp 306. Retrieved 2006-08-21. 
  149. ^ "NASA/IPAC Extragalactic Database". Results for Arp 307. Retrieved 2006-08-21. 
  150. ^ "NASA/IPAC Extragalactic Database". Results for Arp 308. Retrieved 2006-08-21. 
  151. ^ "NASA/IPAC Extragalactic Database". Results for Arp 309. Retrieved 2006-08-21. 
  152. ^ "NASA/IPAC Extragalactic Database". Results for Arp 310. Retrieved 2006-08-21.